distribution of montagu’s harriers ( circus pygargus

Master of Science Thesis by Christian Oskamp

Distribution of Montagu’s Harriers (Circus pygargus) in relation to diversity and abundance of farmland bird prey, in East Groningen, the

Netherlands

Montagu’s Harriers in relation to farmland birds

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Education: MSc Forest- and Nature Conservation, Wageningen University Specialization: Ecology and Management Thesis: Resource Ecology Group, TNV 80337 Period: April 2006– May 2007 Supervisors: Dr. F. de Boer, Resource Ecology Group, Wageningen

Drs. T.M. van der Have, Resource Ecology Group, Wageningen External Supervisors: Ben Koks, Stichting werkgroep Grauwe kiekendief

MSc. Chris Trierweiler, Stichting werkgroep Grauwe kiekendief

Distribution of Montagu’s Harriers (Circus pygargus) in relation to diversity and abundance of farmland bird prey, in East Groningen, the

Netherlands


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Abstract Farmland birds constitute a large proportion of the diet of Montague’s Harriers in the Netherlands, and are therefore an important prey. Not much is known about the importance of the farmland birds in relation to the distribution of the Montagu’s Harrier, most of the research that has been done was focused on the importance of the main prey, the vole. Therefore, this study focused on the relation of the diversity and abundance of farmland birds on the distribution of the Montagu’s Harrier in East Groningen, Germany, and Flevoland. In specific this study focused on three farmland bird species: Yellow Wagtail Motacilla flava, Sky Lark Alauda arvensis, and Meadow Pipit Anthus trivialis. Nest site locations (breeding clusters) and hunting areas of Montagu’s Harriers were chosen as indicators for the distribution of the Montagu’s Harriers. In total 336 point counts were carried out from April to mid July out to determine the relative abundances of the farmland birds.

- Expected was that the nest site locations of Montagu’s Harriers were located in areas where the abundance of farmland birds was higher than areas where no nests were located. The analysis indicated that there was no significant difference in relative abundances of farmland birds near nest site locations compared to areas without nests.

- The abundance of farmland birds was significantly higher inside the hunting areas than outside the hunting area. - There was no relation found between the diversity of the bird prey species and the distribution of hunting area and

breeding clusters of Montagu’s Harriers. Hence, the abundance of the farmland birds had a larger effect on the distribution of the Montagu’s Harrier more than the bird species diversity. Montagu’s Harriers in the Netherlands hunted bird prey species that were most abundant, and are characteristic for open country. Yellow Wagtail appeared to be the most abundant species in the research areas. Sky Lark was the third most abundant and Meadow Pipit the fifth. However, these three species formed the main bird prey (72%) in diet of Montagu’s Harriers in the Netherlands, and Rheiderland, Germany in 2006. From this I conclude that Montagu’s Harriers in the Netherlands are opportunistic specialists, specializing on relatively few species that are locally and temporarily highly abundant

- Slightly more fledgelings were produced in the area where the farmland bird abundances were highest, in Germany, and less fledgelings were produced in the area with the lowest farmland bird abundances, Flevoland. However, these differences were not significant.

This research showed that there is a relation between the abundance of farmland birds and the distribution of the hunting areas of the Montagu’s Harriers in the Netherlands. Accordingly, birds are an important prey species. Therefore, it seems important to create good conditions for farmland birds which could lead to a higher and more stable food supply in for instance bad vole years. This may contribute to a stable or larger population of Montagu’s Harriers, in an effort to make them less susceptible to food supply fluctuations.


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Preface This thesis presents results from a research that has been conducted from April 2006 to May 2007 as a completion of the Master study Forest- & Nature Conservation for the Resource Ecology Group, Wageningen University. The thesis is part of the project ‘Demography and conservation of the Montagu’s Harrier’, conducted by the Dutch Montagu’s harrier foundation. I would like to use this preface to thank all the people that have helped me during my field study and report writing. In specific I would like to thank Jelle Dijkstra, Jan Ploeger, Bauke Koole, Simone van der Sijs, Klaas Steenbergen and Jaap Tonkens, the volunteers who helped me conducting the points counts. I also would like to thank Kees van Scharenburg who gave me advice how to implement the point counts. Also thanks to Silvan Puijman and Dirk Brul of “Het Groninger Landschap” who guided my through the Dollardkwelders during to the points counts. Furthermore, I would like to thank Ruurd Jelle van der Leij and Erik Visser who both helped me a lot during my field work. It was really fine living in Kostverloren for four months with Clara and Rene van Rijn, and I would like to thank them for taking good care. I also would like to thank my supervisors Fred de Boer en Tom van der Have who helped me out with the whole thesis process, from proposal-writing to report-writing, and who gave me really good supervision. Further, I would also like to thank Ben Koks and Christiane Trierweiler, my supervisors of the Dutch Montagu’s Harrier foundation, who gave me the opportunity to do this research, and also helped me with my whole thesis process. Of course I would like to thank my family and friends and everybody else who is not mentioned here but helped me in one way or another with my thesis. Wageningen, May 2007 Christian Oskamp


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Contents 1. Introduction 11

1.1 Background 12 1.2 Study area 12

1.2.1 Groningen 12 1.2.2 Flevoland 12 1.2.3 Germany 12

2. Research questions 13

2.1 Main research question 13 2.2 Sub research question 13 2.3 Hypothesis 13

3. Methods 15

3.1 Data Collection 15 3.1.1 Point counts 15 3.1.2 Nest site location and Breeding parameters 16 3.1.3 Hunting area 17

3.2 Data Analysis 17 3.2.1 Difference between areas 17 3.2.2 Difference between hunting areas and breeding clusters 17 3.2.3 Shannon Weaver diversity index 17 3.2.4 Breeding success 18 3.2.5 GIS mapping 18

4. Results 19 4.1 Descriptive statistics 19

4.1.1 Difference between areas 19 4.1.2 Seasonal change 19

4.2 Non-Paramatic tests 21 4.2.1 Breeding clusters 21 4.2.2 Hunting area 1 21 4.2.3 Hunting area 2 21

4.3 Logistic regression 23 4.3.1 Breeding clusters 23 4.3.2 Hunting area 1 23 4.3.3 Hunting area 2 23

4.4 Diversity 24 4.5 Breeding success

5. Discussion 27

5.1 Breeding clusters 27 5.2 Hunting area 27 5.3 Bird species diversity vs. abundance 27 5.4 Breeding success 29

6. Conclusions 31 6.1 Breeding clusters 31 6.2 Hunting area 31 6.3 Bird species diversity vs. abundance 31 6.4 Breeding success 31 6.5 Recommendations 31

7. References 34 Appendix I Field Form 37 Appendix II Box plots seasonal change 39 Appendix III Histograms predicted probability linear regression 43 Appendix IV Density maps of farmland birds 49 Appendix V Total list of recorded birds 51 Appendix VI List of identified bird prey species in 2006 55


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1. Introduction 1.1 background This research is part of the project “Demography and Conservation of Montagu’s Harriers”, conducted by the Dutch Montagu's Harrier Foundation. The aim of this research project is to contribute to knowledge of the ecology of the Montagu’s Harrier (Circus pygargus). The project focuses on the relation of Montagu’s Harriers with their food sources, spatial behaviour, time budgets, migrations routes, winter ecology, and population dynamics on European level. These results should form the basis for a better conservation of this endangered species. Until the 19th century, the Montagu’s Harrier was a common breeding bird in the Netherlands with an estimated minimum of 500 breeding pairs (Zijlstra & Hustings 1992). At that time, there was a large choice of natural breeding and hunting habitats: heaths, moors, wet meadows, swamps and other uncultivated land. With the cultivation of these areas and the intensification of agriculture, the number of breeding pairs declined to only 4 pairs in 1987 (Koks et al. 2001). In 1988, large parts of agricultural land were set-aside according to EU agricultural policy. These set-aside fields caused a large increase of the vole-population (Microtus arvalis) as well as an increase in the number of breeding pairs of farmland birds. This increase of a potential food source led to an increase of raptors in the area, amongst which Montagu’s Harrier (Zijlstra & Hustings 1992; Koks 1992; Koks & van Scharenburg 1997). When the McSharrry reform of the EU Common Agricultural Policy was implemented in the early 1990’s a peaking in vole density was the result (Koks & van Scharenburg 1997). This amelioration in food supply made the former intensively used arable land a suitable habitat for the Montagu’s Harrier (Koks & van Scharenburg 1997). After the early 1990’s the Mcsharry regulation was replaced by more small scale short lasting site-aside measures, which resulted in a decrease of vole-rich fallow land. Consequently, since around 1993, food supply deteriorated (Koks and Scharenburg 1997). The number of Montagu’s Harriers did not decline dramatically, due to the introduction of agri-environmental schemes and nest-protection. At present, the number of breeding-pairs has stabilised at around 35 in the Netherlands (Koks et al. 2005) (fig 1). Previous studies showed that Montagu’s Harriers in continental Western Europe mostly rely on Common Voles as prey (e.g.Butet & Leroux 2001, Koks et al in press, Krogulec & Leroux 1994). Figure 2 also shows that voles play an essential role in the diet of the Montagu’s Harrier in Groningen. It shows also that when there is a lower proportion of voles in the diet, this gap is filled by the farmland birds. This may indicates that farmland birds play an important role in the diet of the Montague’s Harrier, especially in years with poor vole abundance, farmland birds made up a substantial part of the diet (Koks & van Scharenburg 1997). In 2006 when research was conducted the diet of the Montagu’s Harrier consisted of voles (47%), birds (32%), mammals (5%), insects (12%), and remain (3%). There is not much known about the importance of the farmland birds in relation to the Montagu’s Harrier, most of the research that has been done was focused on the vole. Therefore, this study is focused on the relation of the diversity and abundance of the farmland birds and the distribution of the Montagu’s Harrier in East Groningen, Germany, and Flevoland. A part of the distribution of the Montagu’s Harrier may be determined by food supply (Clark, 1997,

Fig. 1) Number of breeding pairs in the Netherlands from 1990-2006

Number of Breeding pairs

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Fig. 2) Proportion of prey groups in the diet of Montagu’s Harriers in Groningen from 1992-2006

Proportion of diet

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Voles


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Arroyo 1997). So assumed was that the nest site location is a good predictor for high food supply, which might indicates high and divers farmland bird abundance. The Montagu’s Harrier is a ground nesting raptor which often builds nests in crops, mainly in winter cereals in the Netherlands (wheat and barley) (Koks et al. 2002). They may breed semi-colonially, this means nests can be either isolated or in small colonies of 2-5 pairs (pers. comm. Trierweiler). In East Groningen, nests are situated mainly in 4 clusters: Blijham, Meeden, Noordhoek and Dollard polders (pers. comm. Trierweiler.) Besides nesting habitat, the population also needs an adequate food supply in order to maintain population levels (Newton 1998). Therefore hunting area of the Montagu’s harrier, like nest site location, plays an important part in the distribution of the Montagu’s Harrier during the breeding season. So hunting area is also assumed to be a good predictor of high food supplies which could indicates high and divers farmland bird abundances. The farmland birds which are included in the research are Yellow Wagtail (Motacilla flava), Sky Lark (Alauda arvensis), and Meadow Pipit (Anthus trivialis) and are common prey species of the Montagu’s harrier (Koks et al., 1994; Koks & Visser, 1997). Other passerines like Common Starling (Sturnus vulgaris) are also important prey species, only later in the season when large flocks of young starlings are feeding on the grasslands (pers. Comm. Koks). The last decennia’s the numbers of farmland birds declined strong in the Netherlands (SOVON, 2002), and because farmland birds are an important prey specie it is important to know if these numbers affect the distribution the Montagu’s Harrier. As earlier stated, knowledge of the relationship of farmland birds and the distribution of Montagu’s Harrier is limited. Most of the studies that have been conducted were focussed on voles as prey. This study will be focused on distribution of Montagu’s Harrier in relation to the diversity and abundance of farmland bird prey species. The diversity and abundance of farmland birds will be determined by point counts. This method will provide indices for the relative abundance of farmland birds, and the diversity of farmland birds. What can be indicated as a relative high abundance or low abundance of farmland birds can only be defined after more census seasons, this is the first season using this census technique so no data of point counts of previous years is available. The distribution of Montagu’s Harrier is determined by the nest site location and the hunting area of the harriers. The nest site locations will be determined with the knowledge of semi-colonially breeding birds from previous years and by mapping the nest site locations by personal observation. The hunting area will be determined by two methods which will be explained later. The research was conducted in three breeding areas of Montagu’s Harriers: East Groningen, Flevoland, and Rheiderland (Germany). 1.2 Study Area 1.2.1 Groningen The first study sites is located in the eastern part of the province of Groningen (fig 3. number 1), North-East Netherlands (N 53 11, E 74). The relatively uniform, flat and open landscape of East Groningen is mainly used for cultivation of winter wheat and barley, but also for other land uses such as pasture, cultivation of lucerne, sugar beet and oilseed rape. The surface of the study area is approximately 650 km². East Groningen can be classified into two parts. The northern part of the area mainly contains clay soils and the southern part of the area sandy soils. 1.2.2 Flevoland Flevoland (fig 3. number 2) is located in the middle of the Netherlands. This study site is located in the South-West of Flevoland. This part of the Netherlands was in former time’s sea and drained around 1950. The landscape is flat and open and is used for cultivation of potatoes, carrots, wheat and barley. The surface of the area is approximately 200 km². The soil in Flevoland consists of light clay. 1.2.3 Rheiderland, Germany Rheiderland is bordering the study site Groningen. In cultivation it is almost the same as in Groningen only more extensive. The area is also open and flat but less open as in Groningen. The surface of the area is approximately 130 km². The soil in Rheiderland consists of clay.

Fig. 3) Location of the study areas: North East Groningen (1), Flevoland (2), Rheiderland, Germany (3)

3 1

2


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2. Research questions 2.1 Main- research question Is the diversity and abundance of farmland birds correlated with the distribution of Montagu’s Harriers in East Groningen, Flevoland, and Rheiderland (Germany)? 2.2 Sub-research questions Breeding cluster: - Is there a difference in the abundance of farmland birds in- or outside breeding clusters of Montagu’s Harriers? Hunting area: - Is there a difference in the abundance of farmland birds in- and outside hunting areas of Montagu’s Harriers? - Are there areas in Groningen, Germany or Flevoland which have potentially high farmland bird abundance, but are not yet utilized by hunting Montagu’s Harriers? Diversity vs. abundance - Is there a higher species diversity of bird prey in- or outside hunting areas of Montagu’s Harriers? - Is there a higher species diversity of bird prey in- or outside breeding clusters of Montagu’s Harriers? - Are Montagu’s Harriers in the Netherlands specialist or generalists according to diversity and abundance of bird prey? Breeding success: - Do the areas with higher farmland bird abundance have a higher reproductive success than areas with lower farmland bird’s abundances? 2.3 Hypothesis Breeding cluster According to Clark (1997) it is possible that the nest site location is chosen close near places where food resources are clumped. Therefore is expected that the abundance of farmland birds is higher inside the breeding clusters than outside. Hunting area In the agricultural area of Groningen and Germany, passerines like Sky Lark, Meadow Pipit, and Yellow Wagtail occur in relative high abundances. In Flevoland the abundance is lower than in Groningen and Germany (Koks & Visser, pers. comm.). So the hunting distribution of Montagu’s Harrier in Flevoland is expected to be less dependent on farmland birds than in Groningen and Germany. Sky Lark, Meadow Pipit, and Yellow Wagtail are according to Koks and Visser et al (1997) common prey species, so it may be expected that the location of hunting area of the Montagu’s Harrier corresponds with areas where farmland birds occur in relatively high abundances.

Diversity vs. abundance Expected is that the bird prey abundance affects the distribution of Montagu’s Harrier more than prey diversity. Montagu’s Harriers appear to be ‘opportunistic specialists’. Some prey types may be more energetically profitable, and Montagu’s Harriers appear to have a functional response to the prey abundance, hunting them in preference to any other present in the area (Arroyo, 1997). Thus, they are able to switch and specialize in the bird species or other prey that is most abundant in each area. Also according to Arroyo (1997) the Netherlands are cited as one of the countries with least diverse diet for the Montagu’s Harrier. This could indicate that Montagu’s Harriers are specialists or opportunists, hunting preys which are present in high abundances. This conclusion does not hold for East Groningen in 2003 where a high diversity of prey species in the diet was found. This indicates that Montagu’s Harriers in East Groningen behaved as a generalist in 2003 (Trierweiler, 2004). Also Clark (1997) stated that Montagu’s Harrier is very much a generalist predator, but this does not prevent it from specializing on prey that are locally numerous and vulnerable. Breeding success In western France, where voles represent the bulk of harriers diet, harriers breed mostly in areas which contain good food supplies. These areas also produced the most young (Arroyo, 2002). So it seems that were high food abundances occur, the breeding success is higher. Consequently, is expected that Montagu’s Harriers in areas with higher farmland bird abundance, which represent a substantial proportion in the diet of Montagu’s Harrier in the Netherlands, have a higher breeding success than areas with lower farmland bird abundance.


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3. Methods 3.1 Data collection To determine the abundance and diversity of farmland birds in the field, point counts were conducted. All territories of Montagu’s Harrier were mapped and reproduction and breeding success parameters were measured. 3.1.1 Point counts For the first time, farmland birds in East Groningen were monitored by point counts. This method is new for the Netherlands, but already used for a long time in the UK, US, Germany, Finland and France. Since 1984, the BMP-method (Broedvogelmonitoringproject, SOVON) has been used to determine the density of breeding farmland birds. Point counts are just as accurate but more efficient than the territory mapping (similar to BMP) in determining the relative density of farmland birds, according to Cyr et al. (1998). One of the main profits of this method is that with a relatively small amount of time, a large area can be covered. Bijlsma (1998) stated as well that point counts are preferable over the territory mapping to determine the relative densities of birds. The point counts were conducted in the core areas of the Montagu’s Harrier covering the breeding territories and most of the known hunting area. For the point counts a number of points (census stations) were scattered over the landscape, these census stations represented the exact place where the observer was monitoring the birds (fig. 4 & 5). In total 336 census stations were monitored: 277 stations in Groningen (fig. 4), 28 stations in Germany (fig. 4) and 32 stations in Flevoland (fig. 5). During the analyses 14 stations of Groningen were excluded because of data loss. All census stations were visited 4 times each during the breeding season. The breeding season of the farmland birds starts at the beginning of April and last until mid July. Once every three weeks, a replication count was performed. Figure 4 and 5 shows the distribution of the census stations over the areas. The location of the point counts census stations was determined by using the following procedure: with a grid of 1km x 1km squares the stations were equally divided over the area. The points of intersection of the squares were the possible census stations. If the point of intersection was situated on an inferior place (roads, highways, villages, water etc.), these stations were excluded or replaced by a suitable location. Of all qualified stations, the coordinates were noted and each station was given a number. Out of these numbers, 336 stations were selected at random. Approximately 150 stations were monitored by the author, the rest of the stations were monitored by three members and eight volunteers of the Dutch Montagu's Harrier Foundation. During a point count, all birds were recorded during a fixed time period. At all stations, a detection circle with a radius of 200m (12,57ha) was used (van Scharenburg, pers. comm.). All birds within this circle were recorded. Visits started an hour before sunrise and ended 4 to 5 hours after sunrise. The count period for each station was 10 minutes (van Scharenburg, pers. comm.) and was divided in two periods of each 5 minutes. In these periods, all birds were recorded without making a difference between detection distances. A field form was made where the difference between types of observed birds were recorded (see appendix I): Breeding pairs

Fig. 4 Overview of the location of the census points in Groningen and Germany


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(BP): birds that showed territorial behaviour, non-breeding birds (NP): birds that were recorded as individuals that show no territorial behaviour, alarming birds (Alar): birds that were alarming during the count period. This gives an indication whether the birds has young or not (C. van Scharenburg, pers. comm.). Birds flying over, but that were actually not present in the detection area, were noted in a separate column. These were birds that had no relation to the environment of the plot, but did cross the plot during the counting period. Only the first observation of a bird was recorded, whether this was visual or by sound. When it seemed plausible that a bird that starts singing was recorded earlier in the counting period, it was not recorded as a new observation (Hustings et al. 1985). This changes when the bird, which was first recorded as individual, started singing. This bird was then recorded as a breeding pair with territorial behaviour. The ‘best’ observation was recorded (Hustings et al. 1985). During the second 5 minutes observation period, only birds that were not previously observed were recorded. Every replication of monitoring a station was performed at a different starting time. This prevented the observations from being biased by the time of day (Hustings et al., 1985). The exact location of the stations in the field was determined by GPS. To determine the 200 meter radius boundary, reference objects (fence, tree, ditch etc.) were chosen. Because several observers conducted the point counts and the procedure had to be well standardized. Therefore, there were practice counts with all observers before the real count started. The point counts produced indices with (median) relative abundance of the farmland bird species in- or outside the breeding territories and in- or outside the hunting territories. During this research the difference between prey abundance and prey availability was not measured. An additional variable soil, either sand or clay, was included during the analyses. During the point counts also a draft was made of the vegetation types which were inside the 200 meter of the census stations. Because of missing or incomplete field forms during this research it was not possible to include this information in the analysis.

3.1.2 Nest site locations and breeding parameters Breeding pairs of Montagu’s Harriers were located by observations of birds showing mating or nesting behaviour. When a pair was located, observations of a female landing with nest material indicated the exact location of the nest. During nest visits the following parameters were recorded: laying date, wing size, claw size, clutch size, and breeding success. Because not all parameters could be measured for all nest sites only the parameter breeding success (# of fledgelings) was included in the analyses. The breeding clusters were determined as follows: During the breeding period the exact location of the nest site was determined. The four census stations that were closest to the nest site were indicated as inside breeding cluster. In Groningen 54 (20% of total census stations) census stations were determined as inside a breeding cluster, 9 (28%) and 10

Fig. 5 Overview of the location of census points in Flevoland 2006


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(36%) census stations respectively for Germany and Flevoland. The longest distance from census station to nest is a proximally 1,5 km. The contours of the breeding clusters are attached in appendix IV. 3.1.3 Hunting area The hunting area of the Montagu’s Harrier was determined in two ways. With the first method (hunting area 1), a census station was determined as inside the hunting area when during the point counts a hunting Montagu’s Harrier was observed. In total respectively 48 (17%), 7 (22%) and 6 (22%) of all census stations were identified as hunting area 1 for Groningen, Flevoland and Germany. The second hunting area (hunting area 2) was based on the knowledge and 15 year expertise of an expert, Ben Koks (founder of Dutch Montagu’s Harrier foundation). The census stations were selected by plotting the contours of the hunting areas, known from previous years, on a map. The census stations that were inside the hunting area were selected as hunting area. In total 136 (50%), 7 (22%) and 16 (57%) census stations were identified as hunting area 2 for respectively Groningen, Flevoland and Germany. In Flevoland a relative small amount of census stations were identified as hunting area, this area is in a relative early phase of research. Hunting areas are not well known in Flevoland yet (pers. comm. Ben Koks). The contours of hunting areas 1 and 2 are attached in figure 10 and 11. 3. 2 Data analyses 3.2.1 Difference between areas To analyze if there was a difference in abundance of farmland birds between the independent variables Groningen, Flevoland and Germany, a non-paramatic test was preformed, the Mann-Whitney U test for two independent samples. For three or more independent samples the Kruskal-Wallis test was applied. 3.2.2 Difference in Hunting area 1, 2 and Breeding cluster To analyze the difference of abundance inside or outside the hunting- and breeding area a non paramatic test was preformed, the Mann-Whitney U test for two independent samples. This test was also used to analyze the differences of abundance between the soil types sand and clay. A logistic regression was carried out to test the prediction that the probability of encounter a farmland birds was higher inside or outside the breeding cluster and hunting areas. For this analysis only absence (0) or presence (1) at a census station was used. With this analysis it was possible to use more variables at one time to predict the probability of farmland birds occurring inside or outside the breeding area. The predictors that were used are breeding cluster and hunting area (in- or outside cluster/area), area (Groningen, Flevoland, Germany) and soil type (Clay or Sand). These analyses were conducted with the Yellow Wagtail, Sky Lark and Meadow Pipit as dependent variable. These species were also combined in one variable Farmland birds, which was labeled as “Farmland birds total” during the analyses. 3.2.3 Shannon weaver Diversity index The Shannon index H’ is a diversity index used to measure biodiversity. The advantage of this index is that it takes into account the number of species and the evenness of the species. The index is increased either by having more unique species, or by having greater species evenness (Krebs, 1989). The index was calculated with the following formula:

ni : The number of individuals in each species; the abundance of each species

S: The number of species

N: The total number of all individuals:

pi : The relative abundance of each species After the Index numbers were calculated these were tested on differences between inside the hunting area and outside the hunting area and breeding cluster. This was also done for difference in diversity of species for soil type in Groningen, sand and clay. For this test not only the three main species were included but also all other small passerines that occur in the core area of Montagu’s Harriers, and were also found in pellets or prey remains in 2006. The sum of these species was 95% of all identified bird prey species that were found in 2006 (see appendix VI).


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3.2.4 Breeding success Breeding success was analyzed with a Mann-Whitney U test. With this test it was possible to see if there was a difference between the three areas Groningen, Germany and Flevoland. The nest site locations in Groningen were divided in two groups. Of one group the nest site location was situated near sand soils where the Montagu’s Harrier mainly hunted on sandy soils. The nest site location of the second group was situated in the clay area where the Montagu’s Harrier mainly hunted on clayey soils. The difference between the two soil types were also analyzed by the Mann-Whitney U test. All the statistical analyses were performed using the statistical software package SPSS. 3.2.5 Geographic information system (GIS) mapping To visualize the distribution of the abundances of farmland birds the software package Arc View GIS was used. All census stations were plotted in the research area through coordinates. The census stations were linked to tables with indices which contained data about hunting area, breeding area, soil type, and the number of recorded birds per census station. When the extension spatial analyst is activated, the analysis function calculate density becomes available. With this function it is possible to create a density map. The search radius was set on 2000 meter. So all census stations within 2000 meter of each other were linked during the density analyses. GIS calculated a continuous density surface form of all census stations. Therefore it creates a grid theme as output. Each cell within the grid contained the number of recorded birds per km² (100ha) of an area. The cell size of the grid was set in 50 meter. The hunting areas and breeding clusters were visualised by selecting all census stations that were inside the hunting area or breeding cluster. Around these selected stations contours were drawn which represented the hunting area or the breeding cluster.


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4. Results 4.1 Descriptive statistics Firstly, the frequency distribution of the farmland birds observations for Groningen, Flevoland and Germany was tested for normality. None of the dependent variables were normally distributed due to the high numbers of null observations in the point counts. Figure 6 shows the frequency distribution of the Yellow Wagtail observations in Groningen. According to the Kolmogorov-Smirnov test (D(1053) = 0.875, p<0.001), the frequency distribution appears to be non-normal. 4.1.1 Difference between areas The areas were all significant different for all three species of farmland birds. A Scheffe multiple comparison test was applied to distinguish the different areas. The Yellow Wagtail (X² = 96.99, p< 0.001) showed a significantly difference for all three areas (p< 0.001) according to the Scheffe Post Hoc test (fig. 7). The Sky Lark abundances (X² = 68.19, p< 0.001) were significantly different between Groningen and Flevoland ( p< 0.001), and Germany and Flevoland (p< 0.001). No significant difference was found between Groningen and Germany according to the Scheffe Post Hoc test (fig. 7). The Meadow Pipit (X² = 22.87, p< 0.001) showed the same results as the Sky Lark. There was a significant difference between Groningen and Flevoland (p< 0.001), and between Germany and Flevoland (p<0.05). Groningen and Germany showed a similar abundance of the Meadow Pipit (fig. 7) In Groningen the census stations were distinguished in sand or clay. A Mann-Whitney U test was carried out to show the difference between clay and sand. The abundance of Yellow Wagtail and Sky Lark were significantly higher on sandy soils than on clayey soils (U= 108662, p< 0.05, Z= -2.26) (U= 88552.5, p< 0.001, Z= -6,82). The Meadow Pipit did not differ in abundance on sandy soils or clayey soils (U= 117206.5, n.s., Z= -0.39).

4.1.2 Seasonal change To see if there were changes in abundance during the season, box plots were made of the changes in abundances over the season for each species per area (see appendix II). The census of farmland birds consisted of four census rounds. Each round was taken as a time moment. The box plots showed for the Yellow Wagtail an increase in birds. The first census round showed the lowest abundance, followed by an increase in the second round. After that it remained more or the less stable. The abundances Sky Lark remained almost constant during the season. Whereas, the Meadow Pipit fluctuated a little during the season.

Fig. 6 Histogram of distribution of abundance of Yellow Wagtail per census station

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Yel

low

Wag

tail

16

14

12

10

8

6

4

2

0

-2

a

b

c

Area


Sky

Lar

k

16

14

12

10

8

6

4

2

0

-2

a

b

a

Area


Mea

dow

Pip

it

16

14

12

10

8

6

4

2

0

-2

a a b

Fig.7. Box plots of the abundance of the Yellow Wagtail, Sky Lark, and Meadow Pipit. Letters a, b and c indicates if there is a significant differences between areas.

Yellow Wagtail Sky Lark Meadow Pipit


- 20 -

Huntng area 1

Groningen Mean Rank Mann-Whit U Z-value p-value Flevoland Mean Rank Mann-Whit U Z-value p-value

Yellow Wagtail out 507.22 64919 -4.62 0.000 Yellow Wagtail out 64.80 6546 -0.13 0.896

in 616.82 in 65.68

Sky Lark out 511.89 68942 -3.55 0.000 Sky Lark out 64.02 6466 -0.71 0.478

in 595.64 in 68.54

Meadow Pipit out 522.19 77831 -1.23 0.219 Meadow Pipit out 62.68 6330 -1.83 0.068

in 548.86 in 73.38

Farmland bird Total out 500.67 59984 -5.80 0.000 Farmland bird Total out 63.05 6304 -0.89 0.376

in 640.79 in 69.70

Germany Mean Rank Mann-Whit U Z-value p-value

Yellow Wagtail out 50.07 636 -2.79 0.005

in 70.00

Sky Lark out 49.77 610 -3.03 0.002

in 71.06

Meadow Pipit out 54.18 981 -0.23 0.821

in 55.63

Farmland bird Total out 49.48 586 -3.14 0.002

in 72.06

Breeding cluster


Yellow Wagtail out 514,20 87451 -2.57 0.010 Yellow Wagtail out 65,79 1683 -0.43 0.658

in 570,13 in 63,17

Sky Lark out 537,71 89146 -2.17 0.030 Sky Lark out 61,29 1421 -2.15 0.032

in 490,90 in 73,56

Meadow Pipit out 524,86 96108 -0.47 0.638 Meadow Pipit out 59,25 1237 -3.62 0.000

in 534,21 in 78,27

Farmland bird Total out 522,21 94247 -0.75 0.454 Farmland bird Total out 59,46 1287 -2.45 0.014

in 538,80 in 76,00


Yellow Wagtail out 57,98 1185 -1.42 0.157

in 49,43

Sky Lark out 55,97 1314 -0.61 0.545

in 52,36

Meadow Pipit out 57,58 1211 -1.40 0.162

in 50,02

Farmland bird Total out 57,57 1211 -1.24 0.216

in 50,03

Hunting area 2


Yellow Wagtail out 514.50 132090 -1.33 0.184 Yellow Wagtail out 65,79 1683 -0.43 0.658

in 538.74 in 63,17

Sky Lark out 515.75 132729 -1.20 0.230 Sky Lark out 61,29 1421 -2.15 0.032

in 537.56 in 73,56

Meadow Pipit out 517.63 133685 -1.09 0.276 Meadow Pipit out 59,25 1237 -3.62 0.000

in 535.80 in 78,27

Farmland bird Total out 505.90 127701 -2.10 0.036 Farmland bird Total out 59,46 1287 -2.45 0.014

in 544.95 in 76,00


Yellow Wagtail out 44.49 1957 -2.80 0.005

in 61.38

Sky Lark out 42.44 1867 -3.41 0.001

in 62.79

Meadow Pipit out 50.68 2230 -1.19 0.233

in 57.13

Farmland bird Total out 40.92 1800 -3.76 0.000

in 63.84

Table 1 Results of Mann-Whitney test of differences in median abundance in- and outside breeding clusters for Yellow Wagtail, Sky Lark, Meadow Pipit and Farmland bird

Table 2 Results of Mann-Whitney test of differences in median abundance in- and outside hunting area 1 for Yellow Wagtail, Sky Lark, Meadow Pipit and Farmland bird

Table 3 Results of Mann-Whitney test of differences in median abundance in- and outside hunting area 2 for Yellow Wagtail, Sky Lark, Meadow Pipit and Farmland bird


- 21 -

4.2 Non-Paramatic tests 4.2.1 Breeding clusters (table 1) The results of the statistical analysis yielded no consistent difference of bird density when comparing areas inside or outside breeding clusters. Germany had higher abundances of all species and farmland birds outside the breeding cluster, but none of these differences were significant. In Groningen the Yellow Wagtail was significantly more abundant inside the breeding cluster, but on the other hand Sky Lark was significantly more abundant outside the breeding cluster. Flevoland showed a significantly higher abundance inside the breeding cluster for Sky Lark, Meadow Pipit and farmland birds. Yellow Wagtail showed a higher abundance outside the breeding cluster. 4.2.2 Hunting area 1 (table 2) Yellow Wagtail, Sky Lark and farmland birds were all more abundant inside the hunting area than outside in Groningen and Germany. Only the Meadow Pipit showed no significant difference, although the Meadow Pipit was slightly more abundant inside the hunting area. In Flevoland none of the species and the farmland birds showed a significant difference for hunting area 1, but all abundances were higher inside the hunting area than outside. In hunting area 1 it is notable that for all combinations of species and areas the abundance of the birds is higher inside the hunting area. 4.2.3 Hunting area 2 (table 3) Farmland birds were also significantly more abundant inside the hunting area 2 for all areas. In Germany also Yellow Wagtail and Sky Lark were significantly more abundant inside the hunting area. In Flevoland Sky Lark, Meadow Pipit and farmland birds were significantly more abundant inside the hunting area, except for the Yellow Wagtail. The Yellow Wagtail in Flevoland was outside the hunting area more abundant. This is notable because it was the only species that was more abundant outside the hunting area than inside. Hunting area 1 and 2 showed no large difference when comparing the results, both showed mainly a higher abundance inside the hunting area. The analysis of the bird abundance in- and outside the breeding cluster on the other hand did not show a trend. Yellow Wagtail showed the highest abundance and the Meadow Pipit the lowest abundance in all areas. The highest abundance of farmland birds was recorded in Germany and the lowest in Flevoland.


- 22 -

Variables in the Equation

-,294 ,149 3,901 1 ,048 ,746

61,528 2 ,000

-1,000 ,270 13,700 1 ,000 ,368

-2,317 ,320 52,451 1 ,000 ,099

-,626 ,157 15,851 1 ,000 ,535

2,417 ,331 53,359 1 ,000 11,207

BREEDING(1)

AREA

AREA(1)

AREA(2)

SOILTYPE(1)

Constant

Step1

a

B S.E. Wald df Sig. Exp(B)

Variable(s) entered on step 1: BREEDING, AREA, SOILTYPE.a.


-,659 ,169 15,171 1 ,000 ,517

63,459 2 ,000

-1,020 ,271 14,208 1 ,000 ,360

-2,370 ,322 54,295 1 ,000 ,094

-,590 ,152 15,143 1 ,000 ,554

2,736 ,339 65,100 1 ,000 15,425

HUNTING1(1)

AREA

AREA(1)

AREA(2)

SOILTYPE(1)

Constant

Step1

a


Variable(s) entered on step 1: HUNTING1, AREA, SOILTYPE.a.

Table 4 to 6 Output Binary logistic regression of the Yellow Wagtail for differences in the probability of encountering a birds specie in breeding area, Hunting area 1 and Hunting area 2.


-,063 ,129 ,234 1 ,628 ,939

55,924 2 ,000

-1,010 ,270 13,988 1 ,000 ,364

-2,302 ,328 49,354 1 ,000 ,100

-,521 ,152 11,823 1 ,001 ,594

2,157 ,301 51,488 1 ,000 8,643

HUNTING2(1)

AREA

AREA(1)

AREA(2)

SOILTYPE(1)

Constant

Step1

a



4 5

6

Table 13 to 15 Output Binary logistic regression of Farmland bird total for differences in the probability of encountering a birds specie in breeding area, Hunting area 1 and Hunting area 2.


-.354 .224 2.484 1 .115 .702

65.592 2 .000

-.085 .372 .052 1 .819 .919

-1.846 .394 21.989 1 .000 .158

.095 .227 .176 1 .675 1.100

2.525 .461 29.942 1 .000 12.489

Breeding(1)

Area

Area(1)

Area(2)

Soiltype(1)

Constant

Step1

a


Variable(s) entered on step 1: Breeding, Area, Soiltype.a.


-.989 .291 11.565 1 .001 .372

67.234 2 .000

-.100 .372 .072 1 .788 .905

-1.904 .396 23.157 1 .000 .149

.137 .219 .390 1 .533 1.147

3.091 .494 39.105 1 .000 22.008

Hunting1(1)

Area

Area(1)

Area(2)

Soiltype(1)

Constant

Step1

a


Variable(s) entered on step 1: Hunting1, Area, Soiltype.a.


.085 .200 .182 1 .670 1.089

58.034 2 .000

-.121 .372 .106 1 .744 .886

-1.925 .411 21.978 1 .000 .146

.187 .221 .720 1 .396 1.206

2.177 .414 27.706 1 .000 8.816

Huning2(1)

Area

Area(1)

Area(2)

Soiltype(1)

Constant

Step1

a


Variable(s) entered on step 1: Huning2, Area, Soiltype.a.

13 14

15

Table 10 to 12 Output Binary logistic regression of the Meadow Pipit fo differences in the probability of encountering a birds specie in r breeding area, Hunting area 1 and Hunting area 2.


-,174 ,140 1,543 1 ,214 ,840

15,181 2 ,001

,019 ,210 ,009 1 ,926 1,020

-,840 ,286 8,630 1 ,003 ,432

-,117 ,143 ,671 1 ,413 ,890

-,117 ,270 ,187 1 ,666 ,890

BREEDING(1)

AREA

AREA(1)

AREA(2)

SOILTYPE(1)

Constant

Step1

a




-,204 ,146 1,950 1 ,163 ,815

15,475 2 ,000

,009 ,209 ,002 1 ,965 1,009

-,858 ,286 9,010 1 ,003 ,424

-,077 ,135 ,323 1 ,570 ,926

-,101 ,269 ,142 1 ,706 ,904

HUNTING1(1)

AREA

AREA(1)

AREA(2)

SOILTYPE(1)

Constant

Step1

a




-,128 ,120 1,133 1 ,287 ,880

12,535 2 ,002

,022 ,210 ,011 1 ,915 1,023

-,783 ,294 7,099 1 ,008 ,457

-,038 ,136 ,077 1 ,781 ,963

-,247 ,239 1,067 1 ,302 ,781

HUNTING2(1)

AREA

AREA(1)

AREA(2)

SOILTYPE(1)

Constant

Step1

a



11 10

12


-,146 ,146 1,009 1 ,315 ,864

62,574 2 ,000

-,856 ,251 11,624 1 ,001 ,425

-2,261 ,308 53,730 1 ,000 ,104

-,776 ,160 23,588 1 ,000 ,460

2,228 ,315 50,104 1 ,000 9,279

BREEDING(1)

AREA

AREA(1)

AREA(2)

SOILTYPE(1)

Constant

Step1

a




-,806 ,171 22,158 1 ,000 ,447

64,550 2 ,000

-,871 ,253 11,887 1 ,001 ,418

-2,324 ,312 55,550 1 ,000 ,098

-,802 ,154 26,972 1 ,000 ,448

2,825 ,328 74,057 1 ,000 16,857

HUNTING1(1)

AREA

AREA(1)

AREA(2)

SOILTYPE(1)

Constant

Step1

a




,019 ,129 ,022 1 ,883 1,019

59,041 2 ,000

-,869 ,251 11,943 1 ,001 ,419

-2,285 ,317 51,939 1 ,000 ,102

-,732 ,154 22,505 1 ,000 ,481

2,087 ,285 53,542 1 ,000 8,062

HUNTING2(1)

AREA

AREA(1)

AREA(2)

SOILTYPE(1)

Constant

Step1

a



8 7

9

Table 7 to 9 Output Binary logistic regression of the Sky Lark for differences in the probability of encountering a birds specie in breeding area, Hunting area 1 and Hunting area 2.

Variables in Equation: Breeding/Hunting: in- or outside Area: Germany Area (1): Groningen Area (2): Flevoland Soil type: Sand and Clay


- 23 -

4.3 Logistic regression 4.3.1 Breeding cluster The logistic regression showed that only the Yellow Wagtail had a higher probability to be encountered inside the breeding clusters than outside (table 4). The other species, Sky Lark, Meadow Pipit and farm land birds showed also a higher probability to be encountered inside the breeding cluster but these differences were not significant (table 7, 10, 13). The area with the highest encounter rate was Germany followed by Groningen, and the area with the lowest encounter rate was Flevoland. For Yellow Wagtail and Sky Lark these differences between areas were all significant (table 4 and 7). Meadow Pipits and Farmland birds showed only a significant difference in probability with Flevoland compared to the other areas. Germany and Groningen were very similar for these bird species. The Yellow Wagtail and Sky Lark had a significantly higher encounter rate on sand soils (table 4 and 7). Meadow Pipit and Farmland birds showed no significant difference when comparing the probabilities between soil types. 4.3.2 Hunting area 1 In hunting area 1 the probability to encounter a Yellow Wagtail, Sky Lark or Meadow Pipit was higher inside the hunting area than outside. Only for the Meadow Pipit this difference was not significant (table 5, 8 and 11). Also Farmland birds showed a significant higher encounter rate inside the hunting area than outside (table 14). Just like the breeding cluster, the area with the highest encounter rate was Germany followed by Groningen and Flevoland. Also for Yellow Wagtail and Sky Lark these differences were significant (table 5 and 8). Again Meadow Pipit and Farmland birds had a significant lower encounter rate in Flevoland compared to Germany and Groningen (table 11 and 14). The Yellow Wagtail and Sky Lark had a significant higher encounter rate on sandy soils (table 5 and 8). Meadow Pipit and farmland birds showed no significantly difference when comparing the probabilities between soil types. Hunting area 1 also showed a good fit when the contours of the hunting areas 1 were plotted on the map of the predicted probabilities for encountering a farmland bird (fig.10). 4.3.3 Hunting area 2 Hunting area 2 showed very different results than hunting area 1. For all species and farmland birds there is almost no difference in the probability to encounter one of the species in or outside the hunting area (table 6, 9, 12 and 15). The area with the highest encounter rate was Germany followed by Groningen and the area with the lowest encounter rate was Flevoland. For Yellow Wagtail and Sky Lark these differences between areas were all significant (table 6 and 9). Meadow Pipits and Farmland birds showed only a significant difference of encountering when Flevoland was compared to the other areas. The Yellow Wagtail and Sky Lark had a significant higher encounter rate on sand soils (table 6 and 9). Meadow Pipit and Farmland birds showed no significantly difference when comparing the probabilities between soil types. Like hunting area 1, hunting area 2 showed a good fit when the contours of hunting area 2 were plotted on the map of predicted probabilities to encounter a farmland bird (fig.11). All results showed a Nagelkerke R² of 0.11 or lower, so the explained variance in the data was relatively low. Summarizing the above results, the Yellow Wagtail had the highest encounter rate (0.90) inside the hunting area in Germany. And the lowest encounter rate (0, 29) was in Flevoland outside the hunting area. The Sky Lark showed the highest encounter rate (0.88) in Germany inside the hunting area. In Groningen the encounter rate of the Sky Lark was also 0.88 but on sandy soils. The lowest encounter rate (0.25) was in Flevoland outside the hunting area. The best area to encounter a Meadow Pipit (0.48) was in Groningen inside the hunting area on sand soils. The area with the lowest rate (0.22) to encounter a Meadow Pipit was just like the other species in Flevoland outside the hunting area. The highest chance to encounter a farmland bird was in Germany inside the hunting area (0.96), the lowest rate (0.58) occurred in Flevoland outside the hunting area. The values of the predicted probabilities for all species are illustrated in the graphs in Appendix III.


- 24 -

4.4 Diversity In Groningen there was no significant difference between in- or outside the hunting areas and breeding area, although the results showed that there was a slightly higher bird diversity inside the hunting areas 1. Hunting area 2 and breeding cluster showed more bird diversity outside. However, on sand the diversity was significantly higher ((U= 4465,5, p< 0.000, Z= -5.102) than on clayey soils. Figure 8 clearly illustrates that the diversity in the southern part of the area is higher than in the northern. Flevoland showed a similar result, there was no significant difference between the areas inside or outside the hunting or breeding areas. However, all census stations inside the hunting and breeding area showed a slightly higher bird diversity than outside. Germany showed similar results as Groningen, none of the areas showed a significant difference. Hunting area 2 and breeding clusters showed higher diversity outside than inside. Hunting area 1 showed a higher diversity inside.

4.5 Breeding success The results of the analysis for breeding success in number of fledgelings showed no significant difference between the areas. Figure 9 shows that there was a difference between the areas. Also the analysis for failure (successful or failed) of nests with a logistic regression showed no significant difference. In Groningen nest site locations could be divided into two groups. Of one group the nest site location was near hunting area on sandy soils and the other group on clayey soils with hunting area mainly on clayey soils. But also these groups showed no significant difference in number of fledgelings per nest (U= 31.5, n.s., z= -0.821). In Germany the Montague’s Harrier produced the most fledgelings and in Flevoland the least. Figure 12 and 13 shows the nest site locations with the number of fledglings per nest. Remarkable is that all nest site location were situated on clay soils.

Fig 8 Map of Groningen and Germany showing the Shannon – Weaver diversity index

Fig 9 Box plot shows median numbers of fledgelings per nest for the areas Groningen, Flevoland and Germany

Groningen Flevoland Germany

Area

0

1

2

3

4

# o

f F

led

gel

ing

s

S


- 25 -

Fig. 11 Map of Groningen and Germany showing the predicted probability to encounter a farmland birds with the contours of hunting area 2

Fig. 10 Map of Groningen and Germany showing the predicted probability to encounter a farmland bird and the contours of hunting area 1


- 26 -

Fig 12 Map of Groningen and Germany showing the nest site location in 2006 and the number of fledglings per nest

Fig 13 Map of Flevoland showing the nest site location in 2006 and the number of fledglings per nest


- 27 -

5. Discussion

There was a large difference in sample size of point counts between Groningen, Germany, and Flevoland. Therefore, the main conclusion was derived from the area with the largest sample size, Groningen. The areas with the smaller sample sizes, Flevoland and Germany, will be discussed in the light of the results obtained in Groningen. 5.1 Breeding clusters Expected was that the nest site locations of Montagu’s Harriers would be located in areas where the abundance of farmland birds was higher compared to areas where no nests were located. The analysis proved that this was not correct. Unexpectedly, the Sky Lark was more abundant outside the breeding clusters in Groningen, whereas the Yellow Wagtail was more abundant inside the breeding cluster. This could be explained by the fact that Yellow Wagtails were breeding more in wheat and barley field like the Montagu’s Harrier do, and Sky Larks preferred breeding in grasslands and potatoes fields where no nests of the Montagu’s Harrier were located. The results of Germany and Flevoland were not consistent, and did not confirm this. In Germany the results showed even a trend of a higher bird abundance outside the breeding clusters, whereas in Flevoland the bird abundances were slightly higher inside the breeding clusters. In general, no proof was found that there were higher abundances of farmland birds inside the breeding cluster. Apparently, many more factors play a role in the selection of a nest site location. For example predation, the Montagu’s Harrier is a ground nesting species and is therefore more susceptible to predators. So ground nesting birds might choose a nesting place that is particularly well concealed, and evenly spaced (Redmond et al, 1982). This is what Montagu’s Harriers do, they breed mainly in large evenly spaced parcels of wheat and barley (Arroyo, 1997). All nests were relatively close to areas where higher farmland bird abundances were recorded. So an explanation could be that these nest site locations were the best compromise in terms of the distance to the nearest area with a relatively high prey abundance and the lowest nest predation risk. 5.2 Hunting area As expected, the abundance of farmland birds was generally higher inside the hunting areas. In hunting area 1, which was determined by recordings of hunting Montagu’s Harriers during point counts, the difference was highly significant. However, the maps (fig 10 and 11) show that hunting area 2 has a better fit with the areas that show a higher encounter rate of farmland birds. The results indicate that the distribution of the hunting area of Montagu’s Harriers might be influenced by areas with a higher abundance of farmland birds. However, according to Simmons (2000) this could be misleading because the prey abundance is not equal to the prey availability. In most studies that were focused on predator-prey densities, the anti-predator behaviour of the prey was neglected. According to Simmons (2000) prey such as voles are expected to avoid areas where they are vulnerable to predators and congregate in areas where they are least vulnerable. From a predator’s viewpoint one expects that a harrier should hunt voles where with the highest availability, although this is sometimes not in areas with the largest prey density. However, predation pressure alone does not solely determine the spatial habitat use of the different prey species: food, shelter and competition also may play a role. A bird prey is in that way also different than voles. Like other raptors, harriers find birds significantly harder to catch than small mammals (Temeles, 1985). Bird preys are at the far end of the prey agility spectrum according to Newton (1979). Availability of small mammals is related to the vegetation depth and density (Simmons, 2000). For bird prey like farmland birds, this might be less important. They can rely on their agility skills except at the young or egg stage. So there might be no inverse relation with prey abundance such as found for voles. This might explain why the hunting areas of Montagu’s Harriers show a good fit with the areas where high farmland bird abundances were recorded. Bird prey rely on there agility skills and are highly available where high abundances occur, and voles show an inverse relation, they rely on vegetation depth and density and are generally more available where abundances are low, according to Simmons (2000). There were still some areas with a high abundance of farmland birds, or with high predicted probabilities for encountering farmland birds (appendix III) that were not classified as hunting areas by the expert Ben Koks. This could be explained by the fact that the hunting distribution of Montagu’s harriers in the research area is not yet fully known. Other reasons why these areas are not used by harriers could be mobbing by other species like Carrion Crows (Corvus corone) or Gulls while hunting (pers. comm. Ben Koks). The hunting areas were delimited following two different approaches. It appears that hunting area 1 showed a better fit with the predicted prey distribution than hunting area 2. This can be explained by the fact that hunting area 1 is the true hunting area, where during the bird censuses hunting Montagu’s Harriers were recorded. Hunting area 2 was based on the 15 year expertise of Ben Koks in the research area, but as was already mentioned above, the hunting patterns of Montagu’s Harriers might not yet be fully known (pers. comm. Ben Koks). Another confounding factor that could distort the results for hunting area 1 can be the panic that a hunting harrier causes when flying over while monitoring a census station. This causes a lot of activity which can easily lead to more recordings of birds than whiteout panic.


- 28 -

5.3 Bird species diversity versus abundance The result showed no clear relation between the diversity of bird species inside or outside the hunting area and breeding clusters. As expected, the abundance seems to affect the distribution of the Montagu’s Harrier more than diversity does. The five species with the highest abundance were Yellow Wagtail, Common Starling, Sky Lark, Lapwing, and Meadow Pipit. These five species comprised a large proportion (83%) of the total number of identified bird prey in 2006 (appendix VII). Yellow Wagtail was the most abundant species with 10% of all observed birds (figure 14), and was also the species that was most recorded as bird prey species (31%) . Meadow Pipit was the species secondly most frequently recorded as bird prey (22%), and the fifth most abundant species in the surveys. Sky Lark was third most abundant species, and also third most frequently found as bird prey (19%). Common Starling was the second most abundant species recorded, and appeared to be fourth most frequently found bird prey species (9%) (Source: Dutch Montagu’s Harrier Foundation). An explanation for the fact that the Meadow Pipit was less abundant than the Sky Lark and the Common Starling but more frequently caught could be the hunting strategy of Montagu’s Harriers. Montagu’s Harriers seem to prefer hunting along consistent linear landscape elements like ditches, edges of habitats or crop parcels (pers. comm. Ben Koks, Clarks 1996). Meadow Pipits were breeding frequently in the verges of these ditches (pers. observation). So the encounter rate of a Meadow Pipit might have been higher than for the other species. Common Starling was second most abundant, but these abundances were only reported late in the season, when young Starlings fledged and form large flocks. Consequently, they became an interesting prey species for Montagu’s Harriers. So 81% of the total bird prey was formed by species that were also recorded most frequently in the point counts. Only Lapwing showed a high abundance but was not frequently caught by Montagu’s Harriers, but still it was the seventh most frequently caught species (1,9%). These were mostly young Lapwings. It appears that the Montagu’s Harrier hunted bird species that were most abundant, and that presumably had a higher encounter rate then other species. Likewise, all these species prefer open areas where Montagu’s Harrier hunted. From this we may conclude that the Montagu’s Harrier is an opportunistic feeder, the Harriers take bird prey with relative high abundances in open areas. Other studies of prey selection in carnivorous predators also concluded that other predators, like kestrels in England and maned wolfs in Brazil, take prey according to their relative abundances (Jaksic 1989, Village 1982). Diversity only plays a role when the main prey abundances decline. When the abundance of the main prey species decline Steenberg and Kochert (1988) found that the diets of three raptors became more divers. So the abundance of bird prey seemed to affect the distribution of Montagu’s Harrier more than the diversity of bird prey species. However, bird species are not the only component of the diet of Montagu’s Harriers, voles predominate (47%) diet of Montagu’s Harriers in the Netherlands in 2006. Also Lagomorphs, insects, eggs and other mammals are found in the diet (Trierweiler 2004), thereby influencing the diet diversity. This diet diversity also differs in latitude. The diet of the Montagu’s Harriers in Southern Europe and Western Asia are more diverse than that of Montagu’s Harriers in Northern Europe. In these areas prey is more diverse (see for overview Arroyo 1997), including prey items like reptiles and a larger variety of insect species. So the diets of Montagu’s Harriers differ regionally. But Montagu’s Harriers are specialized in prey items that are

Fig14. Bar graph showing the 10 most abundant breeding bird species in proportions (%) with the standard deviation

0

2

4

6

8

10

12

14

Yellow

Wag

tail

Starlin

g

Sky La

rk

Lapw

ing

Meado

w Pipi

t

Mallar

dCro

w

Oyste

rcatch

er

Whit

ethro

at

Redsh

ank

pro

p. p

er s

pec

ies

(%)


- 29 -

locally numerous and vulnerable (Clark 1996). Hence, Montagu’s Harrier in the Netherlands and Rheiderland (Germany) are also specialized in species that are locally and temporally highly abundant. These species, Yellow Wagtail, Sky Lark, Meadow Pipit and Common Starling, are characteristic species of open country. Which is preferred by Montagu’s Harriers and will be discussed later on. In the 1960’s and 1970’s, Shipper (1973) found that small mammals made up only 5%-29% of prey items identified from nests in natural habitat, where the diet was dominated by birds. Due to large changes in their natural habitats two decades ago Montagu’s Harriers changed breeding habitats to more agricultural habitats (Koks et al. 2001). Dutch Montagu’s Harriers did not only change breeding habitats, but also took different prey items. Voles nowadays dominate the diet of Dutch Harriers in agricultural habitats (Koks et al 2007). This illustrates that Montagu’s Harrier can switch from birds as main prey in natural habitats to vole as main prey in agricultural habitats, which are probably more available in agricultural habitats. So, Montagu’s Harriers specialize in species of open country and switch to species that are more abundant. Likewise, compared to other raptor species, the Montagu’s Harrier has specializations: the relative small food size and large wings size largely limits it’s prey choice. The small food size limits the Montagu’s Harrier in the size of which prey which it can carry and catch. While the relative large wings force the Montagu’s Harrier to hunt in open areas because it is not agile enough to hunt in scrubs or forests. Accordingly, these physical qualities make a Montagu’s Harrier a specialist in the smaller open-country prey. Montagu’s Harriers can not rely on carrion as a food source, thereby forcing the Harriers to rely more on smaller open-country prey, presumable because of their inability to compete with corvids and more powerful raptors at carcasses (Simmons 2000). Summarizing the above, it seems that Montagu’s Harriers are opportunistic specialist, specializing on relatively few species that are locally and temporarily highly abundant. 5.4 Breeding success The results showed that more young fledged in the areas where the abundance of farmland birds was highest. In Germany the highest abundance of farmland birds were recorded and there the most young fledged. In Flevoland the lowest abundance of farmland bird were recorded and also few young fledged; Groningen occupies an intermediate position with regard to bird abundance and breeding success. However, these differences were not significant. This might be because the sample sizes were small and there was not much variation in the data. We have to take into account that only 32% of the diet consisted of birds. So other food sources might also have influenced the breeding success, especially voles which represented a substantial part of the diet (47%). Other factors might also have affected the breeding success such as agricultural practices, nest protection, predation and weather conditions (Koks et al 2007).


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- 31 -

6. Conclusions 6.1 Breeding cluster There was no relation found between the abundance of farmland birds and the location of the breeding clusters. No consistent difference was founded in terms of farmland bird abundance when comparing point counts inside or outside the breeding cluster. 6.2 Hunting area There was a significantly higher abundance of farmland birds at locations inside the hunting area, compared to outside. The contours of the hunting area of Montagu’s Harriers showed a good fit with high encounter rates of farmland birds. Hence, there is a relation between the relative abundance of farmland birds and the hunting distribution of the Montagu’s Harriers in the Netherlands. Some areas in East Groningen were relatively under exploited by the harriers, they had typically a high farmland bird encounter rate, but the occurrence of Montagu’s Harriers was relatively small. 6.3 Bird Specie diversity vs. abundance There was no significant relation between the diversity of bird prey and the distribution of hunting area or breeding clusters of Montagu’s Harriers. So, the abundance of the farmland birds affected the distribution of the Montagu’s Harrier more than their species diversity. Montagu’s Harriers in the Netherlands hunted bird prey species that were most abundant and which are characteristic for open country. Hence, Montagu’s Harrier in the Netherlands are opportunistic specialists, specializing on relatively few species that are locally and temporarily highly abundant. 6.4 Breeding success There was a small trend that more fledglings were produced in areas where the relative abundance of farmland birds was higher, but these differences were not significant. 6.5 Methods The point counts that were used to gather the data of relative abundances of farmland birds showed to be suitable. It produced indices and maps of relative densities in a relative way. The number of Sky Larks that were recorded equaled the numbers of Sky Larks that were recorded with the territory mapping method (BMP). Point counts only produced numbers of recorded birds covering a larger area in less time compared to territory mapping. But more research is needed to make an adequate comparison between the two methods. Point counts generated valuable information which gave a better insight into the abundance and distribution of farmland birds and other species, contributing to the knowledge of the ecology of the Montagu’s Harrier in the Netherlands, and Rheiderland (Germany). 6.6 Recommendations The first and most important recommendation is that the point counts census method should be continued for more years. The first year led to valuable information of relative abundances of birds in the Netherlands and Germany. This becomes more valuable when the data becomes available for more years. With a time series of a few years it is possible to see fluctuations in the abundance of birds. Also the possible differences in the distribution of farmland birds over the years can be determined and how the Montagu’s Harriers adapt to these chances. The hunting area for this research was determined by observations of hunting harriers and by the expertise of Ben Koks. The best method to obtain a better picture of the hunting area is to fit some males in the different breeding cluster with radio transmitters. This will produce maps where these harriers occur. These maps together with the distribution and abundance maps of the farmland birds would enable a more accurate analysis than the used methods in this study. Because radio telemetry is a very time consuming activity it is also possible to gather all recordings of hunting Montagu’s Harriers. These recordings can be combined with the recordings made during point counts which could improve our knowledge of the distribution of the hunting area of the Montagu’s Harrier and their changes over seasons, and years. Another important recommendation is about the diet of Montagu’s Harrier. Voles are the main prey for Montagu’s Harrier in the Netherlands, but bird preys also are important. Because this study only focused on bird prey it would be advisable to combine all prey types abundances together in one analysis. This will provide a total picture of food sources for the Montagu’s Harrier, enabling an analysis of the seasonal chances in prey abundances. Remarkable was the difference in abundance of farmland birds between the areas Groningen-Germany (relative high abundance) and Flevoland (relative low abundance). The low abundance of farmland birds Yellow Wagtail, Sky Lark, and Meadow Pipit in Flevoland, is maybe compensated with other bird prey or other prey species. More research is needed to answer this question. The vegetation plays an important role in prey availability for Harriers. It is therefore recommended to also record the vegetation types and density or height of the vegetation during the point counts. With this it could be possible to answer the


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question which vegetation type is preferable by prey and by Harriers, and why. This can improve conservation measures which are taken like fauna edges, nature set-asides, and management of road and ditch verges. Farmland birds are important prey species for Montagu’s Harriers, as mentioned earlier. A better food supply could lead to more Harriers pairs and increase the production of fledglings. From a Montagu’s Harriers conservation viewpoint, it would therefore be recommended to create conditions that support higher farmland bird abundances, so improve the food supplies. This could halt the decrease of farmland bird (Sovon, 2002) in areas where these conditions are created. Further research, like mentioned above, is required to determine these conditions of food supplies. These conditions can than be managed in a good way. Not only for the Montagu’s Harrier, but also the farmland birds.


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7. References Arroyo, B.E. 1997. Diet of Montagu’s Harrier Circus pygargus in central Spain: analysis of temporal and geographic variation. Ibis 139: 664-672. Arroyo, B.E. 1998. Effect of diet on the reproductive success of Montagu’s Harrier Circus pygargus. Ibis 140: 690-693. Arroyo, B., García, J.T. & Bretagnolle, V. 2002. Conservation of Montagu’s Harrier Circus pygargus in agricultural areas. Animal Conservation 5: 283-290. Bijlsma, R.G. 1998. Handleiding veldonderzoek Roofvogels (2nd edn). Utrecht: Stichting Uitgeverij Koninklijke Nederlandse Natuurhistorische Vereniging. Butet, A. & Leroux, A.B.A. 1993. Effect of prey on a predator’s breeding success. A 7-year study on common vole (Microtus arvalis) and Montagu’s harrier (Circus pygargus) in a West France marsh. Acta Oecologica 14: 857-865. Clarke, R. 1996. Montagu’s Harrier. Chelmsford: Arlequin Press. Corbacho, C., Sánchez, J.M. & Sánchez, A. 1997. Breeding biology of Montagu’s Harrier Circus pygargus L. in agricultural environments of southwest Spain; comparison with other populations in the western Palearctic. Bird Study 44: 166-175. Cyr A, Lepage D., Freemark K., 1998. Evaluating Point Count Efficiency Relative to Territory Mapping in Cropland Birds. Monitoring Bird Populations by Point Counts, USDA Forest Service, 1998. Husting M.F.H., Kwak R.G.M., Opdam P.F.M., Reijnen M.J.S.M., 1985. Natuurbeheer in Nederlanddeel 3 Vogelinventarisaties, achtergronden, richtlijnen en verslaglegging. Pudoc Wageningen Nederlandse vereniging tot bescherming van vogels Zeist. Jaksic F.M. 1989. Opportunism vs selectivity among carnivorous predators that eat mammalian prey: A statistical test of hypotheses. Oikos, 56, p427-430. Koks B.J., Trierweiler C., Visser E.G., Dijkstra C., Komdeur J., 2007. Do voles make agriculural habtitat attractive to Montagu’s Harriers Circus pygargus? Ibis 2007 Koks, B. & Van Scharenburg, K. 1997. Meerjarige braaklegging: een kans voor vogels, in het bijzonder de Grauwe Kiekendief! De Levende Natuur 98: 218-222. Koks, B., Visser, E., Draaijer, L., Dijkstra, C. & Trierweiler, C. 2005. Grauwe Kiekendieven Circus pygargus in Nederland in 2004. De Takkeling 13: 65-79. Koks, B.J., Van Scharenburg, C.W.M. & Visser, E.G. 2001. Grauwe Kiekendieven Circus pygargus in Nederland: balanceren tussen hoop en vrees. Limosa 74: 121-136. Koks, B.J. & Visser, E.G. 2002. Montagu’s Harrier Circus pygargus in the Netherlands: Does nest protection prevent extinction? Ornithologischer Anzeiger 41: 159-166. Krebs, C. J. (1989). Ecological methodology. New York: Harper & Row. Krogulec J. & A. B. A. Leroux 1994: Breeding Ecology of Montagu’s Harrier Circus pygargus onnatural and reclaimed Marshes in Poland and France. In: Meyburg B.-U. & R. D. Chancellor(eds), Raptor Conservation Today, WWGBP / The Pica Press. Millon, A., Bourrioux, J.-L., Riols, C. & Bretagnolle, V. 2002. Comparative breeding biology of Hen Harrier and Montagu’s Harrier: an 8-year study in north-eastern France. Ibis 144: 94-105. Newton, I. 1998. Population limitation in birds. London: Academic Press.

Newton, I. 1979. Population ecology of raptors, Berkhamsted, London.


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Redmont G.W., Keppie D. M., & Herzog P.W., 1982. Vegatative structure, concealments and succes of nests of two races of Spruce Grouse. Canadian Journal of Ecology 60, 670-675 . Salamolard, M., Butet, A., Leroux, A. & Bretagnolle, V. 2000. Responses of an avian predator to variations in prey density at a temperate latitude. Ecology 81: 2428-2441. Schipper, W.J.A 1973. A comparison of prey selection in sympatric Harriers Circus in Western Europe. Le Gerfaut 63: 17- 120. Simmons R. E., D. M. Avery & G. Avery 1991: Biases in diets determined from pellets and remains: correction factors for a

mammal and bird-eating raptor. J Raptor Res. 25(3): 63-67. Simmons, R.E. 2000. Harriers of the world: their behaviour and ecology. Oxford: Oxford University Press. SOVON, 2002. Broedvogel atlas van Nederland. Snyder, H. 2001. Hawks and Allies. Pp. 212-224 in C. Elphick, J. Dunning, D. Sibley, eds. The Sibley Guide to Bird Life & Behavior. New York: Alfred A. Knopf, Inc. Steenhof, K. & Kochert, M.N. , 1988. Dietary responses of three raptor species to changing prey densities in a natural environment. Journal of Ecology, 57, p. 37-48 Temeles, E.J. 1985. Sexual size dimorphism of bird-eating Hawks: The effect of prey vulnerability. American Naturalist 125, 485-499. Thiollay, J. 1994. Family Accipitridae (hawks and eagles). Pp. 52-105 in J. del Hoyo, A. Elliott, J. Sargatal, eds. Handbook of the Birds of the World. Vol. 2. New World Vultures to Guineafowl. Trierweiler C. 2004. Considerations on Demography and Conservation of Montagu's Harrier Circus pygargus in east Groningen, Netherlands Master of Science Thesis, Animal Ecology Group and Animal Behaviour Group University of Groningen, Netherlands. Village. A, 1982. The diet of Kestrels in relation to vole abundance. Bird Study, 29, p 129-138. Zijlstra, M. & Hustings, F. 1992. Teloorgang van de Grauwe Kiekendief, Circus pygargus, als broedvogel in Nederland. Limosa 65: 78-79.


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Appendix I Field form piont counts Montagu’s Harrier Foundation 2006

Veldformulier Punttelling Werkgroep Grauwe Kiekendief Puntnr Datum Waarnemer: Coordinaten O Tijd N Waypoint Opmerkingen (storing, veranderingen etc) Bezoeknr Weer (zie onder) Bewolking Wind Neerslag Zicht 0-5 min 6-10 min 0-10 min Soort BP NP Alar BP NP Alar overvliegend Gele kwikstaart Veldleeuwerik Graspieper Kievit Wilde eend Blauwborst Geelgors Zwarte Kraai Other species:

Binnen waarnemingscirkel

Buiten waarnemingscirkel

man vrouw juveniel man vrouw juveniel Grauwe kiek Bruine kiek Blauwe kiek Toelichting weertype aantal Bewolking: 0% geen bewolking - 100% geheel bewolkt BP: één broedpaar Hazen Wind: geen, zacht, matig, hard, stormachtig(richting N,W,O,Z) NP: niet broedende Reeen Neerslag: type (miezer,zachte regen,harde regen,stortbui) individuen Muizen Zicht: goed/matig/slecht Alar : Alarmerend Anders


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- 39 -

Appendix II Box plots: Showing seasonal change in numbers for the species Yellow Wagtial, Sky Lark, and Meadow Pipit in 2006 in Groningen, Flevoland, and Germany. Groningen

Visit number

4321

Yel

low

Wag

tail

14

12

10

8

6

4

2

0

Visit number

4321S

ky L

ark

14

12

10

8

6

4

2

0

Visit number

4321

Mea

dow

Pip

it

14

12

10

8

6

4

2

0


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Flevoland

Visit number

4321

Yel

low

Wag

tail

14

12

10

8

6

4

2

0

Visit number

4321

Sky

Lar

k

14

12

10

8

6

4

2

0

Visit number

4321

Mea

dow

Pip

it

14

12

10

8

6

4

2

0


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Germany

Visit number

4321

Yel

low

Wag

tail

14

12

10

8

6

4

2

0

Visit number

4321S

ky L

ark

14

12

10

8

6

4

2

0

Visit number

4321

Mea

dow

Pip

it

14

12

10

8

6

4

2

0


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- 43 -

Appendix III Histograms of predicted probabilities to encounter a Farmland bird by Binary linear regression Yellow Wagtail (YW) in Breeding Cluster (BC), Hunting area 1 (HA1), and Hunting area 2 (HA2):

clay

sand

Soil type

out

in

Breeding area

Bars show Means


Area

0.00000

0.20000

0.40000

0.60000

0.80000

Pre

dic

ted

pro

b Y

W B

C

clay

sand

Soil type

out

in

Hunting area 1

Bars show Medians


Area

0,00000

0,20000

0,40000

0,60000

0,80000

Pre

dic

ted

pro

b Y

W H

A1


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Sky Lark (SL) in Breeding Cluster (BC), Hunting area 1 (HA1), and Hunting area 2 (HA2):

clay

sand

Soil type

out

in

Breeding area

Bars show Means


Area

0.00000

0.20000

0.40000

0.60000

0.80000

Pre

dic

ted

pro

b S

L B

C

clay

sand

Soil type

out

in

Hunting area 2

Bars show Medians


Area

0,00000

0,20000

0,40000

0,60000

0,80000

Pre

dic

ted

pro

b Y

W H

A2


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clay

sand

Soil type

out

in

Hunting area 1

Bars show Medians


Area

0,00000

0,20000

0,40000

0,60000

0,80000

Pre

dic

ted

pro

b S

L H

A1

clay

sand

Soil type

out

in

Hunting area 2

Bars show Medians


Area

0,00000

0,20000

0,40000

0,60000

0,80000

Pre

dic

ted

pro

b S

L H

A2


- 46 -

Meadow Pipit (MP) in Breeding Cluster (BC), Hunting area 1 (HA1), and Hunting area 2 (HA2):

clay

sand

Soil type

out

in

Breeding area

Bars show Means


Area

0.00000

0.20000

0.40000

0.60000

0.80000P

red

icte

d p

rob

MP

BC

clay

sand

Soil type

out

in

Hunting area 1

Bars show Medians


Area

0,00000

0,20000

0,40000

0,60000

0,80000

Pre

dic

ted

pro

b M

P H

A1


- 47 -

Farmland birds (Farm tot)) in Breeding Cluster (BC), Hunting area 1 (H1), and Hunting area 2 (H2):

clay

sand

Soil type

out

in

Hunting area 2

Bars show Medians


Area

0,00000

0,20000

0,40000

0,60000

0,80000

Pre

dic

ted

pro

b M

P H

A2

clay

sand

Soil type

out

in

Breeding area

Bars show Medians


Area

0,00000

0,20000

0,40000

0,60000

0,80000

Pre

dic

ted

pro

b. F

arm

To

t B

C


- 48 -

clay

sand

Soil type

out

in

Hunting area 1

Bars show Medians


Area

0,00000

0,20000

0,40000

0,60000

0,80000

Pre

dic

ted

pro

b. F

arm

To

t H

1

clay

sand

Soil type

out

in

Hunting area 2

Bars show Medians


Area

0,00000

0,20000

0,40000

0,60000

0,80000

Pre

dic

ted

pro

b. F

arm

To

t H

2


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Appendix VI Density Maps of farmland birds


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- 51 -

Appendix V List of recorded birds with the point counts sorted by Euring codes

number euring Dutch name English name Latin name 1 70 Dodaars Little Grebe Tachybaptus ruficollis 2 90 Fuut Great Crested Grebe Podiceps cristatus 3 720 Aalscholver Great Cormorant Phalacrocorax carbo 4 1210 Grote Zilverreiger Great White Egret Casmerodius albus 5 1220 Blauwe Reiger Grey Heron Ardea cinerea 6 1520 Knobbelzwaan Mute Swan Cygnus olor 7 1610 Grauwe Gans Greylag Goose Anser anser 8 1660 Canadese Gans Canada Goose Branta canadensis 9 1670 Brandgans Barnacle Goose Branta leucopsis 10 1700 Nijlgans Egyptian Goose Alopochen aegyptiacus 11 1730 Bergeend Shelduck Tadorna tadorna 12 1790 Smient Wigeon Mareca penelope 13 1820 Krakeend Gadwall Mareca strepera 14 1840 Wintertaling Teal Anas crecca 15 1860 Wilde Eend Mallard Anas platyrhynchos 16 1910 Zomertaling Garganey Anas querquedula 17 1940 Slobeend Shoveler Anas clypeata 18 2030 Kuifeend Tufted Duck Aythya fuligula 19 2600 Bruine Kiekendief Marsh Harrier Circus aeruginosus 20 2610 Blauwe Kiekendief Hen Harrier Circus cyaneus 21 2630 Grauwe Kiekendief Montagu's Harrier Circus pygargus 22 2670 Havik Goshawk Accipiter gentilis 23 2690 Sperwer Sparrowhawk Accipiter nisus 24 2870 Buizerd Buzzard Buteo buteo 25 3040 Torenvalk Lesser Kestrel Falco tinnunculus 26 3090 Smelleken Merlin Falco columbarius 27 3100 Boomvalk Hobby Falco subbuteo 28 3200 Slechtvalk Peregrine Falco peregrinus 29 3670 Patrijs Partridge Perdix perdix 30 3700 Kwartel Common Quail Coturnix coturnix 31 3940 Fazant Pheasant Phasianus colchicus 32 4240 Waterhoen Moorhen Gallinula chloropus 33 4290 Meerkoet Coot Turdus merula 34 4500 Scholekster Oystercatcher Haematopus ostralegus 35 4560 Kluut Avocet Recurvirostra avosetta 36 4690 Kleine Plevier Little Ringed Plover Charadrius dubius 37 4850 Goudplevier Golden Plover Pluvialis apricaria 38 4860 Zilverplevier Grey Plover Pluvialis squatarola 39 4930 Kievit Lapwing Vanellus vanellus 40 5190 Watersnip Snipe Gallinago gallinago 41 5320 Grutto Black-tailed Godwit Limosa limosa 42 5340 Rosse Grutto Bar-tailed Godwit Limosa lapponica 43 5380 Regenwulp Whimbrel Numenius phaeopus 44 5410 Wulp Curlew Numenius arquata 45 5460 Tureluur Redshank Tringa totanus 46 5480 Groenpootruiter Greenshank Tringa nebularia 47 5530 Witgatje Green Sandpiper Tringa ochropus 48 5560 Oeverloper Common Sandpiper Actitis hypoleucos 49 5820 Kokmeeuw Black-headed Gull Larus ridibundus 50 5900 Stormmeeuw Common Gull Larus canus 51 5910 Kleine Mantelmeeuw Lesser Black-backed Gull Larus graellsii 52 5920 Zilvermeeuw Herring Gull Larus argentatus


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53 6000 Grote Mantelmeeuw Great Black-backed Gull Larus marinus 54 6150 Visdief Common Tern Sterna hirundo 55 6680 Holenduif Stock Dove Columba oenas 56 6700 Houtduif Wood Pigeon Columba palumbus 57 6870 Zomertortel Turtle Dove Streptopelia turtur 58 7240 Koekoek Cuckoo Cuculus canorus 59 7950 Gierzwaluw Swift Apus apus 60 8760 Grote Bonte Specht Great Spotted Woodpecker Dendrocopos major 61 9760 Veldleeuwerik Sky Lark Alauda arvensis 62 9810 Oeverzwaluw Sand Martin Riparia riparia 63 9920 Boerenzwaluw Swallow Hirundo rustica 64 10010 Huiszwaluw House Martin Delichon urbica 65 10090 Boompieper Tree Pipit Anthus trivialis 66 10110 Graspieper Meadow Pipit Anthus pratensis 67 10171 Gele Kwikstaart Yellow Wagtail Motacilla flava 68 10201 Witte Kwikstaart White Wagtail Motacilla alba 69 10660 Winterkoning Wren Troglodytes troglodytes 70 10840 Heggenmus Dunnock Prunella modularis 71 10990 Roodborst Robin Erithacus rubecula 72 11060 Blauwborst Bluethroat Luscinia svecica 73 11210 Zwarte Roodstaart Black Redstart Phoenicurus ochruros 74 11370 Paapje Whinchat Saxicola rubetra 75 11390 Roodborsttapuit Stonechat Saxicola rubicola 76 11460 Tapuit Northern Wheatear Oenanthe oenanthe 77 11870 Merel Blackbird Turdus merula 78 12000 Zanglijster Song Thrush Turdus philomelos 79 12010 Koperwiek Redwing Turdus iliacus 80 12020 Grote Lijster Mistle Thrush Turdus viscivorus 81 12360 Sprinkhaanzanger Grasshopper Warbler Acrocephalus naevia 82 12380 Snor Savi's Warbler Locustella luscinioides 83 12430 Rietzanger Sedge Warbler Acrocephalus schoenobaenus 84 12500 Bosrietzanger Marsh Warbler Acrocephalus palustris 85 12510 Kleine Karekiet Reed Warbler Acrocephalus scirpaceus 86 12590 Spotvogel Icterine Warbler Hippolais icterina 87 12740 Braamsluiper Lesser Whitethroat Sylvia curruca 88 12750 Grasmus Whitethroat Sylvia communis 89 12760 Tuinfluiter Garden Warbler Sylvia borin 90 12770 Zwartkop Blackcap Sylvia atricapilla 91 13110 Tjiftjaf Chiffchaff Phylloscopus collybita 92 13120 Fitis Willow Warbler Phylloscopus trochilus 93 14620 Pimpelmees Blue Tit Parus caeruleus 94 14640 Koolmees Great Tit Parus major 95 15390 Gaai Jay Garrulus glandarius 96 15490 Ekster Magpie Pica pica 97 15600 Kauw Jackdaw Corvus monedula 98 15630 Roek Rook Corvus frugilegus 99 15671 Zwarte Kraai Hooded Crow Corvus corone 100 15820 Spreeuw Starling Sturnus vulgaris 101 15910 Huismus House Sparrow Passer domesticus 102 15980 Ringmus Tree Sparrow Passer montanus 103 16360 Vink Chaffinch Fringilla coelebs 104 16380 Keep Brambling Fringilla montifringilla 105 16490 Groenling Greenfinch Chloris chloris 106 16530 Putter Goldfinch Carduelis carduelis


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107 16600 Kneu Linnet Carduelis cannabina 108 18570 Geelgors Yellow Hammer Emberiza citrinella 109 18770 Rietgors Reed Bunting Emberiza schoeniclus 110 20030 Stadsduif Colombo domesticus


- 54 -


- 55 -

Appendix VII Relative composition of identified bird prey species in pellets and prey remains in 2006 (source: Dutch Montagu’s Harrier Foundation)

The column # of bird prey shows de number of birds that where found in pellets or prey remains. The second column shows the proportion of each species of the total bird prey. The column # included shows species and their numbers that were included in the diversity analysis.

Species # of bird prey # included Proportion (%)

Mallard Anas platyrhynchos 1 0,2%

Pheasant Phasianus colchicus 1 0,2%

Sand Piper Calidris alpina 1 0,2%

Redshank Tringa totanus 1 0,2%

Black-tailed Godwit Limosa limosa 1 0,2%

Wader sp. 1 0,2%

Stock dove Colomba oenas 1 0,2%

Tree Pipit Anthus trivialis 1 0,0%

Black redstart Phoenicurus ochruros 1 0,2%

Sedge Warbler Acrocephalus schoenobaenus 1 0,2%

Bearded Tit Panurus biarmicus 1 0,2%

Blue Tit Parus caeruleus 1 0,2%

Goldfinch Carduelis carduelis 1 0,2%

Sparrow sp. Passer sp. 2 0,4%

Greenfinch Carduelis chloris 2 0,4%

Marsh Warbler Acrocephalus palustris 3 0,6%

House Sparrow Passer domesticus 3 0,6%

Montagu’s Harrier Circus pygargus 4 0,8%

White Wagtail Motacilla alba 4 0,8%

Bluethroat Luscinia svecica* 4 4 0,8%

Swallow Hirundo rustica* 6 6 1,2%

Reed Bunting Emberiza schoeniclus* 6 6 1,2%

Common Quail Coturnix coturnix* 7 7 1,3%

Whitethroat Sylvia communis* 8 8 1,5%

Tree Sparrow Passer montanus* 8 8 1,5%

Lapwing Vanellus vanellus* 10 10 1,9%

Yellow Hammer Emberiza citronella* 10 10 1,9%

Linnet Carduelis cannabina* 11 11 2,1%

Common Starling Sturnus vulgaris* 44 44 8,5%

Sky Lark Alauda arvensis* 98 98 18,9%

Meadow Pipit Anthus pratensis* 113 113 21,8%

Yellow Wagtail Motacilla flava* 163 163 31,4%

Total 519 488 100,0%

Percentage 100% 95%

*Species that were included in the Shannon-Weaver diversity analysis

distribution of montagu’s harriers ( circus pygargus

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