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Habitat Selection by White Storks Breeding in a MosaicAgricultural Landscape of Central PolandAuthor(s): Tomasz Janiszewski, Piotr Minias, Zbigniew Wojciechowski, andPatrycja PodlaszczukSource: The Wilson Journal of Ornithology, 126(3):591-599. 2014.Published By: The Wilson Ornithological SocietyDOI: http://dx.doi.org/10.1676/13-219.1URL: http://www.bioone.org/doi/full/10.1676/13-219.1

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The Wilson Journal of Ornithology 126(3):591–599, 2014

Habitat Selection by White Storks Breeding in a Mosaic AgriculturalLandscape of Central Poland

Tomasz Janiszewski,1 Piotr Minias,1,2

Zbigniew Wojciechowski,1 and Patrycja Podlaszczuk1

ABSTRACT.—The number of White Storks (Cico-nia ciconia) has been decreasing in many parts ofEurope at least since the middle of the 20th century.Intensification of agriculture and continuous conversionof natural habitats, such as wetlands, into agriculturallandscapes have been recognized as the most importantdeterminants of dramatic reductions in population sizesof this species. For this reason, providing quantitativeestimates of habitat requirements may allow us toidentify the key biota which should be prioritized forconservation. The aim of this study was to investigateWhite Storks’ habitat selection in a mosaic agricultural

landscape in central Poland. We found that territoriesassociated with large river valleys were highly preferredby first-arriving storks. We also recorded lowerintensity of brood reduction and higher reproductivesuccess of storks breeding in such territories. Thus, itseems likely that location of nests close to river valleysprovided easy access to rich food resources associatedwith wetlands. In fact, distance to nearest wetland wasthe second strongest predictor of nest-site selection inthe studied population. We also demonstrated that pairsnesting in the territories with a high proportion ofwetlands showed lower levels of brood reduction incomparison to pairs having poorer access to wet habitatpatches. Finally, we found that although early arrivingstorks avoided settling in an urbanized landscape, theyselected nesting sites located close to buildings. Theresults of this study confirmed high importance of wet

1 Department of Teacher Training and Biodiversity Studies,

University of Łodz, Banacha 1/3, 90-237, Łodz, Poland.2 Corresponding author; e-mail: pminias@op.pl

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grasslands for the core central European population ofWhite Storks. Received 18 December 2013. Accepted 1March 2014.

Key words: brood reduction, Ciconia ciconia, habitat

structure, nest-site selection, reproductive success, territory

occupation, wetlands.

Information on habitat selection is of growingimportance for conservation of threatened animalpopulations. Understanding how to assess thequality of habitat and how this quality varies inspace is a crucial prerequisite to prioritize areas formanagement and conservation (Morris 2003). InEurope, populations of many avian species have

greatly declined over the last decades because of

intensification of agriculture and continuous con-

version of natural habitats, such as wetlands, into

agricultural landscapes (Chamberlain et al. 2000,

Donald et al. 2001, Tryjanowski et al. 2011). These

factors have been recognized as the most important

determinants of dramatic reductions in the popu-

lation sizes of White Storks (Ciconia ciconia),

especially in the northern and western parts of their

breeding range (Senra and Ales 1992, Carrascal et

al. 1993, Tucker and Heath 1994). The number of

White Storks has been decreasing in many parts of

Europe at least since the middle of the 20th

century. For example, the size of the German

population declined from ,9,000 pairs in the mid-

1930s to slightly over 3,000 pairs in the late 1980s

(Bairlein 1991), and in some countries, including

Sweden (Olsson and Rogers 2009), Switzerland

(Moritzi et al. 2001) and the Netherlands (Doligez

et al. 2004), the species even faced extinction.

It is widely agreed that White Storks largelydepend on various types of grasslands as a suitableforaging habitat (Tryjanowski et al. 2005). Tradi-tionally, storks prefer to forage on wetlands, butbecause of rapidly declining accessibility to suchhabitats, the species has changed its preferences todry agricultural meadows and pastures with lowvegetation. Several studies have demonstratedpredominance of grasslands among foraging habi-tats of White Storks. In Germany, storks spent.95% of foraging time on grasslands, in spite of thefact that they covered ,20% of the area (Bohning-Gaese 1992). However, White Storks tend to nestalso in the vicinity of human settlements, wheregrasslands may be scarce. For this reason, storks arealso known to forage in arable lands, where theyswitch from preying on aquatic animals to differenttypes of terrestrial prey, such as earthworms, insects

and small rodents (Antczak et al. 2002). It has been

suggested that high densities of voles (Microtus sp.)

may facilitate high stork productivity because of

high calorific value of such prey (Tryjanowski and

Kuzniak 2002). Consequently, dry agricultural

landscapes should not necessarily be considered as

a suboptimal habitat for White Storks. In fact,

several studies indicated that storks may avoid

foraging on wetlands and wet meadows, even in

regions with easy access to such habitats (Dziewiaty

1992, Moritzi et al. 2001).

The aim of this study was to investigate habitat

selection of White Storks in a mosaic agricultural

landscape with easy accessibility to different

types of foraging habitats, such as wetlands, dry

grasslands and arable lands. For that purpose, we

investigated the timing of occupation of territories

located in different habitats, as most attractive

patches of habitat are expected to be selected and

occupied earliest in the season by individuals of

high phenotypic quality (Møller 1994, Kokko

1999). We also aimed to assess the quality of each

habitat type by examining how they affected

productivity and occurrence of brood reduction in

a large central Polish population of storks over the

last two decades. Finally, by providing quantita-

tive estimates of habitat requirements, we wanted

to identify the key biota which should be

prioritized for conservation of the species. It is

an important conservation goal to recognize

habitat selection patterns of White Storks in

Poland, because the country holds ,25% of the

world’s population of this species (Jakubiec and

Guziak 1998, Shulz 1998).

METHODS

Habitat selection by White Storks was studied

from 1994–2011 in the Łowicz district (52u 069 N,

19u 569 E), central Poland. The study area of

1,120 km2 was covered mainly with agricultural

landscape crossed by a relatively large (2–3 km

wide) river valley of Bzura. The valley is sparsely

forested with vast open areas of wet meadows and

pastures. There are also several tributaries of

Bzura, which have relatively narrow valleys

(typically up to 500 m, occasionally up to 1 km

wide). These valleys are more extensively wooded

and have a much lower share of the area covered

with open grasslands. In the remaining part of the

study area (beyond the borders of river valleys),

an agricultural landscape with cereals and root

crops prevails. Some parts of this area are highly

592 THE WILSON JOURNAL OF ORNITHOLOGY N Vol. 126, No. 3, September 2014

urbanized or covered with woodlands; wetlandsand grasslands are scarce.

The size of the study population varied from177–209 breeding pairs between years. Each year,researchers surveyed all known active nests andsearched for new nests. Effective location of newterritories in the entire area was possible becauseof the high conspicuousness of stork nests, whichare built on partially withered trees, electricitypylons, roofs of buildings, or chimneys (Tryja-nowski et al. 2009). During each season, wecollected information on the following reproduc-tive parameters: (i) timing of territory occupation;(ii) brood reduction measured with the number ofchicks expelled from the nest before fledging; (iii)reproductive success measured with the numberof raised fledglings. Data were collected only forterritories, where both partners were recorded atthe nest during the season. Territories where onlyone adult/subadult bird was present at the nestwere considered unoccupied and were discountedfrom all analyses.

The information on the timing of territoryoccupation and brood reduction was collectedfrom cooperating farmers, who lived in closeproximity to the nests. Such methodology hasproved reliable (Ptaszyk et al. 2003) and is widelyused in studies on White Storks (e.g., Tryjanowskiand Sparks 2008). The timing of territoryoccupation was recorded with an accuracy ofone day for the first- and the second-arriving pairmember. In White Storks, the first-arriving pairmembers are usually males, which tend to arriveseveral days before females to establish territories(Tryjanowski et al. 2004). Reliable information onthe timing of territory occupation (for both pairmembers) was gathered for 1,386 breedingoccasions that were associated with 233 differentterritories.

Brood reduction was estimated as the numberof nestlings found dead on the ground below storknests throughout the entire pre-fledging period.All cases where factors other than brood reductionwere deemed to contribute to chick death werediscounted from the analyses (e.g., collapse of theentire nest or losses of entire broods afterinclement weather). Intensity of brood reductionestimated with such method was demonstrated towell correlate with territory quality measured byduration of occupancy, suggesting that the methodmay be safely applied for analysis of White Storks(Janiszewski et al. 2013a). The information onbrood reduction was gathered for 1,037 breeding

attempts (n 5 234 territories). Reproductivesuccess was assessed by surveying all active nestsin July, a period when nestlings are already fullygrown and preparing to leave the nest. Number offledglings was recorded for each breeding pair bydirect observation with binoculars. In total, thedata on reproductive success was collected for3,316 breeding attempts (n 5 293 territories).

For each territory, we also measured 15different habitat parameters using 1:50,000 topo-graphic maps. Percentage land use within 4-kmradius of each nest (50.27 km2) was measured forthe following categories of habitat: wetlands(flooded and wet meadows, marshes), grassland(dry meadows and pastures), woodland, arableland, built environment (defined as area coveredby buildings), and open water (calculated for allwater bodies excluding watercourses). A distanceof 4 km was chosen to evaluate proportions ofeach habitat type, as it is consistent with anaverage size of foraging territories for WhiteStorks (Alonso et al. 1991, Bohning-Gaese 1992,Johst et al. 2001, Moritzi et al. 2001). Extensivebehavioral observations confirmed that a largemajority of foraging trips in the studied storkpopulation did not exceed 4 km (Podlaszczuk2012). Within the same radius of each nest, wemeasured a total length of rivers (defined aswatercourses wider than 5 m), streams (all smallerwatercourses), and roads (only paved roadsincluded). We also measured distances from eachnest to the nearest wetland, grassland, andwatercourse (rivers and streams all together),which were expected to constitute attractiveforaging grounds for White Storks. Finally, wemeasured distance to the nearest town (defined ashuman settlement with more than 1,000 inhabi-tants), nearest paved road, and nearest building.The last parameter was considered zero, if nestwas placed directly on a building.

In order to avoid pseudoreplication of the data(Hurlbert 1984), the mean inter-seasonal values ofoccupation dates and reproductive parameterswere calculated for each territory and assignedas units of all analyses. The differences in theshare of each habitat type within foragingterritories, as well as in the distances to selectedforaging habitats were analyzed with ANOVA.Post-hoc comparisons were conducted with Tukeytest. All habitat variables, except for total streamlength, were log-transformed to improve normal-ity. Prior to the multivariate analysis, we usedPearson product-moment correlation to check

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whether any of the variables were highly corre-

lated, i.e., |r| . 0.7. Since arable land area showed

strong negative correlation with woodland area

(r 5 20.71, n 5 240, P , 0.001), we decided to

remove the latter variable from further analyses.

The impact of the remaining 14 habitat charac-

teristics on reproductive parameters of storks

(timing of territory occupation, number of chicks

expelled from the nest, number of fledglings) was

analyzed with General Linear Models (GLM).

The strength of support for each model (relative to

all other models) was evaluated using Akaike’s

Information Criterion corrected for small sample

sizes (AICC). The correction for small sample

sizes was applied to AIC as the total number of

data points divided with the number of explana-

tory variables was ,40 for some of the models

(Burnham and Anderson 1998). AICC is consid-

ered the most efficient statistical tool to select

models with best predictive abilities (Burnham

and Anderson 1998, 2004). The best fitting

models have the lowest AICC and models with

DAICC , 1 are considered equivalent. To find the

model with lowest AICC, we used a combination

of backward and forward searches, with different

initial models as used in other avian ecology

studies (e.g., Bustnes et al. 2001). The character

and strength of explanatory variables included in

best fitting models were evaluated with bcoefficients of regression lines. Percent of vari-

ance in the dependent variable explained by

particular independent factors was evaluated with

partial eta-squared g2 (Cohen 1973). All values

are presented as means 6 SE. All statisticalanalyses were performed using Statistica 10.0(Statsoft, Tulsa, OK, USA).

RESULTS

Habitat Characteristics.—There were signifi-cant differences in the share of each habitat typewithin foraging territories of storks (F5,1524 5

3843.3, P , 0.001). The territories of WhiteStorks from the studied population were mostlycovered with arable lands, which on averagecomprised 71.9% of territory area (Table 1). Theshare of grasslands and woodlands within territo-ries was much lower (on average, 10.0% and9.4% of territory area, respectively). The lowestpercentage of foraging territory area was coveredwith built environment (3.6%), open water (1.4%),and wetlands (1.0%). Consistently, for an averagenest, the distance to nearest wetland was muchgreater than the distance to nearest grassland and tonearest watercourse (F2,762 5 197.6, P , 0.001;Tukey: all P , 0.001; Table 1). Although most ofnests were located far from large human settle-ments (on average 8.49 6 0.24 km from nearesttown), storks on average nested in direct vicinity ofbuildings (mean distance to nearest building: 0.0246 0.005 km; Table 1).

Timing of Territory Occupation.—There wasstrong evidence that early arriving storks settled inthe close vicinity of river valleys. Total riverlength within a territory was included in the bestfitting models for the timing of territory occupa-tion by both pair members (Table 2) and account-

TABLE 1. Habitat variables measured for breeding territories of White Storks in central Poland.

Variable Mean SE Min Max

Wetland area (km2) 0.51 0.04 0.00 2.73

Meadow area (km2) 5.03 0.22 0.00 13.12

Woodland area (km2) 4.73 0.34 0.00 35.49

Arable land area (km2) 36.14 0.39 10.66 47.50

Built-environment area (km2) 1.82 0.09 0.34 9.67

Open water area (km2) 0.69 0.06 0.00 3.65

Total river length (km) 7.33 0.37 0.00 21.50

Total stream length (km) 70.86 1.22 22.80 123.60

Total road length (km) 25.84 0.60 4.30 53.40

Distance to nearest wetland (km) 1.66 0.08 0.10 6.00

Distance to nearest grassland (km) 0.64 0.04 0.01 4.50

Distance to nearest watercourse (km) 0.22 0.01 0.01 1.00

Distance to nearest road (km) 0.39 0.03 0.01 2.40

Distance to nearest building (km) 0.024 0.005 0.00 1.05

Distance to nearest town (km) 8.49 0.24 0.45 17.25

594 THE WILSON JOURNAL OF ORNITHOLOGY N Vol. 126, No. 3, September 2014

ed for the highest proportion of variance among

all analyzed variables (4.2% and 5.0% for the

first- and the second-arriving pair member,

respectively). Distance to nearest wetland wasalso a strong predictor of the timing of territory

occupation, as nest sites located closer to wetlands

were preferred by early arriving storks (Table 3).

We also found moderate support for the effects of

built-environment area and nearest building dis-

tance on the timing of territory occupation

(Table 2). We found that although early arriving

storks avoided settling in highly urbanized land-

scape, they selected for nesting sites that werelocated close to the buildings (Table 3). Finally,

distance to nearest road was included in the best

fitting models, indicating that nesting sites located

close to roads were not readily selected by the early

arriving individuals (Table 3).

Brood Reduction and Reproductive Success.—

Total river length within a territory was found to

be the best predictor of the magnitude of brood

reduction, measured with the number of chicks

expelled from the nest (Table 2). We found that

storks that held territories in the vicinity of rivervalleys expelled lower number of nestlings fromthe nest (Table 3). Wetland area was the secondhabitat parameter included in the best fittingmodel, indicating that the number of chicksexpelled from the nest decreased with the percentarea of territory covered by wetlands (Table 3).The other habitat variables that were associatedwith the timing of territory occupation did notaffect the magnitude of brood reduction (DAICC

. 1).

The only variable included in the best fittingmodel was total river length (Table 2), confirminghigh significance of river valleys for the produc-tivity of storks (Table 3). All the other habitatparameters were found to reduce the fit of thefinal model (Table 2).

DISCUSSION

In this study we confirmed high importance ofwet grassland habitats for the population of WhiteStorks from central Poland. We found a strongeffect of total river length within foraging

TABLE 2. Models explaining habitat variation in the timing of territory occupation (for both pair members), number of

chicks expelled from the nest, and reproductive success of White Storks in central Poland, 1994–2011. Models were ranked

by ascending AICC. AICC values are given for the best model (MB1), the second (MB2) and third (MB3) best models, and

for the best model when removing one parameter at the time (MB1 – x). K stands for the number of parameters. The

following habitat variables are included: ALA – arable land area, BE – built environment, RD – road distance, DW –

distance to nearest wetland, TRL – total river length, NBD – nearest building distance, WA - wetland area, DR – distance to

nearest river.

Dependent variable Model AICC K

Timing of territory occupation by the first pair member

MB1 5 DW + TRL + BE + NBD + RD 1396.62 5

MB2 5 MB1 – RD 1397.26 4

MB3 5 MB1 – BE – NBD 1397.26 3

MB1 – BE 1397.38 4

MB1 – NBD 1397.38 4

MB1 – TRL 1398.50 4

Timing of territory occupation by the second pair member

MB1 5 DW + TRL + BE + NBD + RD 1390.04 5

MB2 5 MB1 – RD 1390.23 4

MB3 5 MB1 – NBD 1391.06 4

MB1 – BE 1392.54 4

Number of chicks expelled from the nest

MB1 5 WA + TRL 454.31 2

MB2 5 MB1 + ALA 454.48 3

MB3 5 MB1 + ALA + DR 455.62 4

MB1 – WA 455.72 1

MB1 – TRL 456.29 1

Reproductive success

MB1 5 TRL 565.24 1

MB2 5 MB1 + ALA 565.42 2

MB3 5 MB1 + DR 565.46 2

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territories on the timing of territory occupation

and productivity. This means that territoriesassociated with river valleys were largely pre-

ferred by first-arriving individuals. We alsorecorded lower intensity of brood reduction and

higher reproductive success of storks breeding insuch territories. For this reasons, it seems likely

that location of nests close to river valleysprovided easy access to rich food resources

associated with wetlands. In fact, distance tonearest wetland was the second strongest predic-

tor of nest-site selection in the studied populationof White Storks. High profitability of wetlands for

storks was confirmed with the analysis of broodreduction. We demonstrated that pairs nesting in

the territories with high proportion of landcovered by wetlands on average expelled lower

number of nestlings from the nests in comparisonto pairs that nested in the territories with lower

share of wet habitat patches. This seems to giverelatively strong support for the hypothesis that

wetlands tend to provide much higher foodavailability for White Storks, which is reflected

by the storks’ ability to successfully rear a higherproportion of hatchlings there. However, in spite

of this relationship, we failed to find any evidencefor an impact of wetlands on the reproductive

success within the studied population.

Although habitat selection was extensively

studied for the central European populations ofthe White Stork, most of the research has focused

on nest-site distribution and density, not takinginto account productivity of storks breeding in

different habitat patches. One of the exceptionswas the study conducted in northeast Poland,

which demonstrated strong preference of storks tonest along the edges of the Biebrza Valley

(Nowakowski 2003). This area was recognizedas an optimal nesting habitat for storks, as it was

associated with high reproductive success of pairs.Territories located at the edges of the valley had

better access to certain types of habitat whichprovided abundant food resources, such as wet

meadows and pastures. On the other hand, largeconcentrations of nests were also recorded in

close vicinity to vast complexes of green crops(Nowakowski 2003). Similar findings were pre-

sented by Ptaszyk (1994), who found thatbreeding density of storks in western Poland

depended on the proportion of meadows andpastures within the territories. The highest stork

densities were recorded in the valleys of large ormedium-size rivers and in the areas with abundant

wet meadows and peat bogs that were adjacent tolakes of different types (Ptaszyk 1994). Consis-

tently, the other study from western Poland

TABLE 3. Parameter estimates (b) for the best models explaining habitat variation in the timing of territory occupation

(for both pair members), number of chicks expelled from the nest, and reproductive success of White Storks in central

Poland, 1994–2011. Model selection based on AICC values in Table 2. g2 indicates the proportion of variance in the

dependent variable explained by particular habitat characteristics.

Dependent variable b SE F P g2

Timing of territory occupation by the first pair member

Total river length 21.97 0.69 8.24 0.005 0.042

Distance to nearest wetland 1.33 0.68 3.89 0.050 0.020

Nearest building distance 1.14 0.64 2.79 0.097 0.015

Built environment 1.17 0.70 2.78 0.097 0.015

Road distance 21.12 0.68 2.66 0.104 0.014

Timing of territory occupation by the second pair member

Total river length 22.12 0.68 9.79 0.002 0.050

Built environment 1.56 0.69 5.18 0.024 0.027

Distance to nearest wetland 1.41 0.66 4.50 0.035 0.024

Nearest building distance 1.16 0.67 3.03 0.083 0.016

Road distance 21.00 0.67 2.21 0.138 0.012

Number of chicks expelled from the nest

Total river length 20.108 0.054 4.04 0.046 0.019

Wetland area 20.089 0.051 3.02 0.084 0.015

Reproductive success

Total river length 0.098 0.049 3.92 0.049 0.015

596 THE WILSON JOURNAL OF ORNITHOLOGY N Vol. 126, No. 3, September 2014

showed that the size of a local population ofWhite Storks was regulated by the presence ofgrazed pastures in the nearby Obra River Valley(Tryjanowski et al. 2005). Dense breeding aggre-gations of White Storks were also associated withhigh percentage of intensively used grasslands inBrandenburg, Germany, but the greatest part ofvariation in stork density was explained by theproportion of mixed agricultural landscape, wheregrasslands were fragmented by crop fields (Latusand Kujawa 2005). Similarly, distribution ofWhite Storks in eastern Germany was highlydependent on the presence of grasslands andinshore waters, as well as on the diversity oflandscape structure (Latus et al. 2000). Historicaldata also prove that occurrence of White Storks incentral Europe was determined by accessibility tograsslands, as demonstrated for the former EastPrussia in the late 1940s (Wickert et al. 2010).Accessibility to flooded or wet meadows andpastures was a key determinant of stork abun-dance also in the Iberian (Alonso et al. 1991,Carrascal et al. 1993) and south Europeanpopulations (Radovic and Tepic 2009).

In our study, habitat selection was analyzed withthe timing of arrival of both pair members at theirterritories. We assumed that territories which wereoccupied earliest in the season should be of highestattractiveness for individuals returning from win-tering quarters. This assumption was based on thefact, that the timing of arrival in birds is considereda phenotype-dependent process (Møller 1994). Inmost studied migratory species, individuals of highphenotypic quality (expressed with age, experi-ence, or physical condition) have capabilities tobetter deal with the challenge of migration andusually arrive earlier at the breeding grounds (e.g.,Lozano et al. 1996, Cooper et al. 2011). Inconsequence, early-arriving males gain priority inaccess to best-quality territories and, simultaneous-ly, are able to attract females of high phenotypicquality (Kokko 1999, Forstmeier 2002). Fitnessbenefits associated with early arrival have alsobeen reported for White Storks (Tryjanowski andSparks 2008, but see Janiszewski et al. 2013b).Therefore, it has to be acknowledged that therelationships between certain habitat characteris-tics and productivity of storks may be, at least tosome extent, mediated by variation in the quality ofbreeding pairs. We can assume that the mostattractive territories are likely to be occupied byolder and more experienced individuals who areable to out compete conspecifics of poorer quality

and relegate them to less profitable nesting sites(Vergara et al. 2007). For this reason, higherproductivity of pairs nesting in high-qualityterritories may not only be attributed to betteraccessibility to rich food resources, but also fromintrinsic characteristics of adults, although we lackany empirical evidence to confirm this hypothesis.However, the tendency of a high-quality pair tosettle in territories that were located close to rivervalleys and wetlands strongly indicates thatexploitation of these habitats should also carrydirect benefits in terms of fitness.

Nest-site selection of storks from the centralPolish population was not only associated withaccessibility to favorable foraging grounds but alsodepended on the presence of human settlements.We found that although early arriving storksavoided settling in an urbanized landscape, theystill selected nesting sites located close to build-ings. There was also a moderate negative effect ofdistance to nearest paved road on the timing ofterritory occupation in the studied population. Overthe last centuries, the traditional system of colonialnesting in the riverine forests has become increas-ingly rare in the White Storks (Schulz 1998).Instead, storks have become attracted to nesting inthe proximity of human settlements, as agriculturallandscapes provided easy access to food resources,as well as reduced pressure from large predators(Dziewiaty 1992, Schulz 1998). In spite of suchpreferences, we found that storks did not readilychoose highly urbanized landscapes for nesting,because those areas are likely to limit accessibilityto attractive foraging habitats. Built-up areas havealready been suggested as important disturbancesfor distribution of White Storks in central Europe(Kaatz 1999), which is consistent with patternsrecorded for other farmland species (Kuitunen et al.1998). Also in Spain, the largest reductions in thepopulation sizes of White Storks have beenrecorded in the areas with greater human activity,including urbanization (Senra and Ales 1992).

We found that territories associated with largeriver valleys were highly preferred by White Storksbreeding in a mosaic agricultural landscape ofcentral Poland. It was demonstrated that storksbreeding in such territories showed lower intensityof brood reduction and higher reproductive suc-cess. For these reasons, it seems likely that locationof nests close to river valleys provided easy accessto rich food resources. The results of this studyconfirm high importance of wet grasslands for thecore central European population of White Storks.

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ACKNOWLEDGMENTS

We would like to thank all the people participating in

the fieldwork, especially Radosław Włodarczyk. We are

grateful to all the farmers who provided data on the arrival

dates and brood reduction. PM was financially supported by

the Scientific Foundation of the University of Łodz. We

also wish to thank Piotr Tryjanowski and two anonymous

reviewers for helpful comments on an earlier draft of the

manuscript.

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