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Association between avian communities and vegetationstructure in a low-lying woodland-savanna ecosystemin SwazilandAra MonadjemPublished online: 12 Nov 2009.

To cite this article: Ara Monadjem (2005) Association between avian communities and vegetation structure in alow-lying woodland-savanna ecosystem in Swaziland, Ostrich: Journal of African Ornithology, 76:1-2, 45-55, DOI:10.2989/00306520509485472

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OSTRICHEISSN 1727–947X

Association between avian communities and vegetation structure in alow-lying woodland-savanna ecosystem in Swaziland

Ara MonadjemDepartment of Biological Sciences, University of Swaziland, Private Bag 4, Kwaluseni, Swaziland

e-mail: ara@uniswacc.uniswa.sz

The community structure and population density of birds was studied at 10 sites in three broad woodland types in the lowveldof Swaziland. Birds were surveyed on a monthly basis at 12 locations per site using a standard point count technique. Eachsite was surveyed over a 12-month period. Vegetation characteristics of each location were recorded. Both cluster analysisand non-metric multidimensional scaling using bird densities, grouped the sites into two main habitats: riparian and non-riparian. The non-riparian habitat was further divisible into Acacia savanna and broadleaved woodland. A similar classificationwas obtained using vegetation characteristics. Principal components analysis (PCA) of the vegetation characteristics wasconducted. The first axis (accounting for 57.7% of the total variation) represented variation in tree cover below 3.5m and grasscover above 0.25m. The second axis (24.8%) represented variation in tree cover above 3.5m and grass cover below 0.25m.These two axes accounted for 82.5% of the total variation. In general, the Acacia sites had lower tree cover and high grasscover, the broadleaved woodland sites had higher tree cover below 3.5m, and the riparian sites had the highest tree cover.Acacia savanna recorded the highest species richness of birds (128 species) with lower numbers recorded in riparian (101)and broadleaved woodland (94). A total of 161 species of birds was recorded across all sites, of which 48 species wererecorded on fewer than four occasions, and 51 species were recorded in all three habitats. Of the remaining species, 14species were confined to Acacia savanna, 14 species to riparian, and two species to broadleaved, woodland. Broadleavedwoodland supports a depauperate, but indistinct, avian community compared to that of Acacia savanna; riverine forest, incontrast, supports a different set of species.

Vegetation structure (or physiognomy) is known to have amajor influence on the distribution and abundance of birds(Rotenberry and Wiens 1980, Kikkawa 1982). Avian speciesdiversity generally increases with increased foliage heightdiversity or increased woody vegetation (Wilson 1974,Herremans 1993, Pomeroy and Dranzoa 1997), but plantspecies composition (or floristics) may also strongly affectavian communities (Rotenberry 1985). Furthermore,individual bird species often demonstrate strong preferencesfor certain vegetation types, thus permitting vegetationparameters to describe avian habitats (Collins et al. 1982,Rice et al. 1983, Koen and Crowe 1987).

The structure of African savannas is predominantlydetermined by rainfall, fire, nutrients and herbivory (Scholesand Walker 1993, Roques et al. 2001). Avian distributionsmay be related to these differences in vegetation structureboth on a biogeographical and a local scale (Benson andIrwin 1966, Milewski and Campbell 1976, Lack 1987), withdifferences in avian communities between broadleaved andfine-leaved savannas often being emphasised (Tarboton1980). Broadleaved savannas or woodlands are typicallydominated by non-Acacia trees, while fine-leaved savannaspredominantly consist of Acacia species. Over much ofsouth-central Africa, broadleaved savannas are dominatedby trees from the genus Brachystegia, while further south innorthern South Africa the dominant tree is Burkea africana(Scholes and Walker 1993). Both of these tree genera are,

however, absent from Swaziland, where broadleavedsavannas are dominated by Combretum and Terminaliaspecies (Sweet and Khumalo 1994). Brachystegia woodlandsupports a number of endemic species of birds (Benson andIrwin 1966) while the avian community inhabiting Burkeasavanna is distinct from that of neighbouring Acacia-dominated savannas (Tarboton 1980).

In Swaziland, low-lying savannas are typically dividedinto Acacia savanna and broadleaved woodland withnarrow, interdigitating strips of riverine forest runningthrough both (Hess et al. 1990). Recent studies have beenconducted on the population density, seasonal fluctuationand community structure of birds in all three of thesesavanna-woodland types in Swaziland (Monadjem 2001a,2001b, 2002a, 2002b, 2003). Using these data, this papersets out to determine whether differences in aviancommunity composition reflect differences in vegetationstructure.

Study area

Swaziland is a small, landlocked country in southern Africacovering approximately 17 360km2. The lowveld ofSwaziland lies in the eastern half of the country at altitudesbelow 500m, and is separated from the Mozambique coastalplains by the Lubombo mountain range (Goudie and PriceWilliams 1983). Altitude ranges from 150m to 400m above

Introduction

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sea level. Mean monthly temperature in January is 26°C andin July is 18°C, while mean annual rainfall ranges from550mm to 725mm. The vegetation can be classified aslowveld savanna (Acocks 1988) with broadleaved woodlandpredominating in the west, microphyllous (Acacia) savannain the east, and riverine forest along rivers and majordrainage lines (Hess et al. 1990, Sweet and Khumalo 1994,Roques et al. 2001). Riverine forest in Swaziland typicallysupports large, evergreen trees that often contrast sharplywith shorter, deciduous trees in adjacent savannas. Hence,three broad-scale vegetation associations or habitats can bedistinguished in the lowveld of Swaziland: Acacia savanna,broadleaved woodland and riverine forest. Characteristictree species associated with each of these habitats are:Acacia nigrescens, A. tortilis, Ziziphus mucronata,Sclerocarya birrea and Dichrostachys cinerea (Acaciasavanna); Combretum apiculatum, C. zeyheri, Terminaliasericea, Peltophorum africanum, Maytenus senegalensis,and several species of Euclea (broadleaved woodland);Ficus sycomorus, Trichilia emetica, Schotia brachypetalaand several species of Acacia (riverine forest) (Sweet andKhumalo 1994).

Field work was conducted at 10 sites in the lowveld ofSwaziland, of which four were in Acacia savanna (MlawulaNature Reserve, Hlane National Park, Mhlosinga NatureReserve and Nisela Safaris) and three each in broadleavedwoodland (Dinedor Cattle Ranch, Mkhaya Game Reserveand Inyoni Yami Swaziland Irrigation Scheme (IYSIS) CattleRanch) and riverine forest (Mhlosinga Nature Reserve,Mkhaya Game Reserve and IYSIS Cattle Ranch) (seeFigure 1). These study sites were chosen for their largeareas of ‘undisturbed’ Acacia savanna, broadleavedwoodland or riverine forest (Monadjem 2002a, 2002b,2003).

Methods

Each of the three broad-scale habitats was sampled over aone-year period with the sites in Acacia savanna beingvisited between June 1998 and May 1999, the sites inbroadleaved woodland between September 1999 andAugust 2000, and the riverine forest sites betweenSeptember 2000 and August 2001. Sites were sampled on amonthly basis, and each site was visited a total of 12 times.

Bird populations were censured using the ‘point count’technique (Gibbons et al. 1996, Monadjem 2002a). At eachof the 10 study sites, 12 randomly selected, fixed locations(at least 100m apart) were established. Birds were countedduring a 10min period, once a month at each location. Birdswere recorded as occurring either within or beyond a 30mradius and the density of each species was calculated usingthe formula in Greenwood (1996):

density (birds/ha) = [(n1 + n2)/π(r2)m]loge[(n1 + n2)/n2]

where r = radius of zone, n1 = number of birds countedwithin r, n2 = number of birds counted beyond r and m =number of replicate points in the set.

At each of the 12 locations (within each of the 10 sites),nine vegetation characteristics were estimated (following

Herremans 1993, Monadjem 2002a) (Table 1). Percentcover was recorded in the following categories: 0 = <1%cover, 1 = 1–5%, 2 = 6–25%, 3 = 26–50%, 4 = 51–75% and5 = 76–100%. Percent cover in each of the nine categorieswas averaged over the 12 locations at each site to provide amean value for each category per site. In addition, theShannon-Weiner index (H’) of structural diversity(Herremans 1993) was calculated for each site. This indexwas initially calculated for each category; these were thenadded together to return a single value per site. It is believedthat this technique, though simple, effectively describesqualitative differences in vegetation structure between the10 sites. Pearson’s correlation co-efficient was used toascertain whether densities of individual bird species wereassociated with vegetation characteristics at the 10 sites.For this analysis, cover values for Grass1 and Herb1 werecombined to provide a total cover value for that particularstratum. The same was applied to Grass2 and Herb2. Thereason for this was that there was little herb cover at mostsites. Only bird species recorded four or more times wereincluded in this analysis, to prevent low-density species(which may have been overlooked at some sites) fromskewing the results.

Multivariate analysisAll multivariate statistics were performed using the softwarepackage PRIMER (Clarke and Gorley 2001). Principalcomponents analysis (PCA) was performed on the 10vegetation characteristics (mentioned above) at the 10 sites.Non-metric multi-dimensional scaling (MDS) was used toplot the 10 sites in relation to each other based on the birdsrecorded within each site. Cluster analysis was employed togenerate dendrograms based on Bray-Curtis similaritiescomputed on standardised densities of bird species at eachsite. Densities were square-rooted so as to down-weight thecontributions of a few superabundant species in relation torarer species (Clarke and Warwick 1994). ANOSIM (basedon the Bray-Curtis similarities) was used to detect significantdifferences between the different communities, as identifiedby the cluster analysis. Finally, SIMPER was used todetermine which species contributed most to thesedifferences between communities.

Results

Bird distributionsA total of 161 species of birds was recorded at the 10 sites.Species richness was greatest in Acacia savanna (128species recorded in the point counts), followed by riverineforest (101 species) and lowest in broadleaved woodland(94 species). Bird densities were similar in Acacia savanna(25.5 birds/ha) and riverine forest (26.6 birds/ha), but farlower in broadleaved woodland (12.7 birds/ha).

Of the 161 species, 48 (30%) species were recorded onless than four occasions and have been omitted from thefollowing analysis. Fourteen species were restricted to eachof Acacia savanna and riverine forest, whilst only twospecies were restricted to broadleaved woodland (Table 2).Acacia savanna and broadleaved woodland shared thegreatest number of species, followed by Acacia savanna

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and riverine forest, with riverine forest and broadleavedwoodland sharing the fewest species (Table 2). Theremaining 51 species occurred in all habitats. Hence, a largenumber of species occurred throughout the three vegetationtypes, with equal numbers of species restricted to Acaciasavanna and riverine forest. Very few species wererestricted to broadleaved woodland.

Of the total of 161 species, 18 species were recorded atall 10 sites with a further 13 species having been recordedat nine of the sites. These 31 (19%) species can beconsidered ubiquitous in the low-lying woodland-savannasof Swaziland (see Appendix 1). The densities of 20 of thesespecies, however, varied considerably between habitats(Appendix 1). For example, Apalis flavida was recorded atall 10 sites, but its density was significantly higher in riverineforest than either Acacia savanna or broadleaved woodland.Densities of the remaining 11 species did not differsignificantly between the three habitats, suggesting thatthese species do not have habitat preferences(corresponding with vegetation types) within the low-lyinglowveld savanna-woodlands of Swaziland.

Vegetation profilesThe vegetation profiles of the three different habitats areshown in Figure 2. At all three sites, grass and herb coverwas greatest near the ground and rapidly decreased awayfrom it. For both the Acacia and broadleaved savanna sites,tree cover was greatest between 1.0–3.5m above ground. Inriverine forest, however, cover was greatest between3.5–7.0m above ground, and cover was still high beyond7.0m above the ground. In constrast, cover diminishedrapidly above 7.0m in Acacia and broadleaved savanna. Ingeneral, grass cover was highest in Acacia savanna,intermediate in riverine forest and lowest in broadleavedwoodland. Tree cover, however, was lowest in Acacia andhighest in riverine forest, where trees were alsoconsiderably taller than in the other two habitats. However,structural diversity of vegetation was highest in Acaciasavanna and lowest in broadleaved woodland (Table 3).

A total of 72 species of birds was recorded at four ormore of the 10 sites, of which 37 species exhibitedsignificant correlations with vegetation structure.Associations between densities of these species andvegetation characteristics are presented in Appendix 2.These species associations can be categorised into threebasic groups; those species associated with: 1) grass cover2) thicket cover (plants below 3.5m tall) 3) tree cover (plantsabove 3.5m tall). Nine species demonstrated correlationswith grass cover, 17 species with thicket cover and 28species with tree cover.

Multivariate analysesThe PCA analysis of the vegetation characteristics producedthree main groupings: the riverine sites, the broadleavedwoodland sites and the Acacia savanna sites (Figure 3). Thefirst PCA axis, accounting for 57.7% of the variance, is agradient from tall, closed woodland to open savanna with aconcomitant increase in the cover of short grass (Table 4).The second PCA axis, accounting for 24.8% of the variance,is a gradient from short, dense thickets to open shrubland

Figure 1: Map of Swaziland showing the sampling sites. A =Mlawula Nature Reserve (Acacia), B = Hlane National Park(Acacia), C = Mhlosinga Nature Reserve (Acacia, riverine), D =Nisela Safaris (Acacia), E = IYSIS Cattle Ranch (broadleaved,riverine), F = Mkhaya Game Reserve (broadleaved, riverine), G =Dinedor Cattle Ranch (broadleaved). The lowveld is shown inhatched

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Table 1: The nine vegetation characteristics measured at 12 loca-tions within each of the 10 sites

1. Per cent grass cover in the height class 0–0.25m (Grass 1)2. Per cent grass cover in the height class 0.25–1m (Grass 2)3. Per cent grass cover in the height class >1m (Grass 3)4. Per cent herb cover in the height class 0–0.25m (Herb 1)5. Per cent herb cover in the height class 0.25–1m (Herb 2)6. Per cent cover by bushes and trees in the height class 0–1m

(Tree 1)7. Per cent cover by bushes and trees in the height class 1–3.5m

(Tree 2)8. Per cent cover by bushes and trees in the height class 3.5–7m

(Tree 3)9. Per cent cover by bushes and trees in the height class 7–14m

(Tree 4)

Table 2: Number of species restricted to different habitats orcombinations of habitats in low-lying savannas of Swaziland.Values in parentheses indicate proportions of the total (113)species. Habitats are listed in order of decreasing species richness

Habitat(s) No. of speciesAll habitats 51 (45%)Acacia-broadleaved combined 15 (13%)Acacia savanna 14 (12%)Riverine forest 14 (12%)Acacia-riverine combined 10 (9%)Riverine-broadleaved combined 7 (6%)Broadleaved woodland 2 (2%)Total* 113

*excludes species recorded on less than four occasions

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and a concomitant increase in the cover of tall grass (Table4). The first two axes account for more than 82% of thevariance, suggesting that differences in vegetation structureat the 10 sites are adequately described by these two axes.

Cluster analysis of the 10 sites based on bird densitiesproduced three main groupings (Figure 4) corresponding tothe three groups produced by PCA analysis of vegetationvariables (Figure 3); the riverine sites grouped together, as didthe broadleaved woodland sites and the Acacia savanna sites.

MDS ordination of the 10 sites produced the same threegroupings, namely riverine sites, broadleaved woodlandsites and Acacia savanna sites (Figure 5). Since the stressfunction is well below 0.05, the ordination provides ‘anexcellent representation with no prospect ofmisinterpretation’ (Clarke and Warwick 1994). These threecommunities are significantly different from each other(ANOSIM, R = 0.975, P < 0.01). Hence, the vegetation isdivisible into three physiognomically discrete types eachsupporting a distinct avian community.

Between seven and nine species contributed 50% of thedissimilarity between the three communities (Table 5).Granivorous finches (Estrildidae) and canaries (Fringillidae)accounted for four of the nine species contributing 50% ofthe dissimilarity between Acacia savanna and broadleavedwoodland, and two out of eight species between Acaciasavanna and riverine forest. Only one species (Prionopsplumatus) that is listed in Table 5 is predominantly abroadleaved woodland species (Appendix 1).

Discussion

The results of this study clearly demonstrate that thecomposition of bird communities inhabiting low-lyingsavannas in Swaziland differs between the three majorvegetation types occurring there, namely Acacia savanna,broadleaved woodland and riverine forest. Although such ananalysis has not been conducted for birds inhabitingsavannas elsewhere in southern Africa, these findings arecomparable with a few previous studies. Tarboton (1980)

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Figure 2: Vegetation profiles of the three broad habitats. Refer toTable 1 and the text for an explanation of the seven strata

Table 3: Summary of vegetation characteristics of the three habitats in low-lying savanna in Swaziland. The Shannon-Weiner index (H’) wasused to represent the structural diversity of the vegetation (see text)

Vegetation stratum Acacia savanna Broadleaved woodland Riverine forestTotal cover: grass-herbs 7.2 3.9 5.4Total cover: trees-bushes 5.1 7.9 12.2Total cover: all strata 12.3 11.8 17.6Structural diversity (H’) 0.72 0.62 0.67

Figure 3: Principal components analysis of the vegetationcharacteristics at the 10 sites in Swaziland. A = Acacia savannasites; B = broadleaved woodland sites; R = riverine forest sites

Table 4: Ordination statistics for principal components analysis(PCA) of vegetation characteristics and 10 sites in Swaziland. Thevalues are correlations of the principal components withstandardised vegetation variables (see Methods) for axes 1 and 2.See Table 1 for an explanation of the vegetation variables

Vegetation variable Axis 1 Axis 2Grass 1 0.394 0.047Grass 2 0.207 0.481Grass 3 0.354 0.293Herb 1 0.363 0.237Herb 2 0.327 0.335Tree 1 0.268 0.449Tree 2 0.239 0.515Tree 3 0.409 0.04Tree 4 0.377 0.207Eigenvalue 5.19 2.23% var* 57.7 24.8

*percent of variance accounted for by each axis

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reported higher densities of fewer resident avian species inAcacia woodland compared with adjoining Burkea(broadleaved) woodland in northern South Africa. This resultdiffers considerably from that observed in Swaziland, whereAcacia savanna supports both higher species richness andhigher densities of birds than broadleaved woodland(Monadjem 2002b). Furthermore, considerably morespecies were restricted to Acacia savanna than tobroadleaved woodland (Table 2), supporting the contentionthat the avian community in broadleaved woodland(dominated by Combretum and Terminalia) is a depauperateversion of that occurring in Acacia savanna (Monadjem2002b). Hence, the major difference in avian communities ofthese two habitats is in the absence of certain species frombroadleaved woodland, rather than the presence of a uniqueassemblage there. The avifauna of broadleaved woodlandsin Swaziland, therefore, are quite different from thosebroadleaved woodlands to the north (Monadjem 2002b).

At Tarboton’s (1980) study site, for example,broadleaved woodland supported 125 species (comparedwith 130 species in Acacia woodland), of which 13 specieswere exclusively found in this habitat. Included among thesespecies were six species-pairs of congeners in which onemember of the pair was present in each woodland. Another27 species were resident in broadleaved woodland but only

sporadically observed in Acacia woodland. This clearlyindicates a unique bird assemblage associated withbroadleaved woodland.

Why then does broadleaved woodland in Swaziland notsupport a distinct bird community? The reason may beassociated with the fact that broadleaved woodland inSwaziland is dominated by combretaceous vegetation whilebroadleaved woodland in subtropical Africa is typicallydominated by Brachystegia (or Burkea in the case ofTarboton’s study site). Hence, both floristics andphysiognomy may differ between these habitats looselylumped as broadleaved woodlands. Furthermore, severalspecies typically associated with broadleaved woodlandselsewhere in Africa are only found in Acacia savanna inSwaziland including Halcyon chelicuti and Melaenornispallidus. Other ‘typical’ species of broadleaved woodlandssuch as Melaenornis pammelaina, Cinnyricinclusleucogaster, Parus niger, Tchagra senegala andDendropicus fuscescens (Tarboton 1980) occur at higherdensities in Acacia savanna than in broadleaved woodlandin Swaziland. In conclusion, it would appear thatcombretaceous woodlands support an entirely differentavifauna to those woodlands dominated by Burkea orBrachystegia, but similar (albeit depauperate) to Acaciasavanna in Swaziland (Monadjem 2002b).

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Figure 4: Classification of the 10 sites based on standardised aviandensities using Bray-Curtis similarities. Acacia savanna sites:Nisela, Mhlosinga, Mlawula and Hlane. Broadleaved woodlandsites: Mhkaya, Dinedor and Tshaneni. Riverine forest sites: MkhayaR, Tshaneni R and Mhlosinga R

Figure 5: Non-metric multidimensional scaling of the 10 sites usingstandardised avian densities. A = Acacia savanna sites; B =broadleaved woodland sites; R = riverine forest sites

Table 5: Species contributing a cumulative 50% of the dissimilarity between the three broad habitats. Species are listed in order of importance

Acacia/Broadleaved Acacia/Riverine Broadleaved/RiverineUraeginthus angolensisa Uraeginthus angolensisa Camaroptera brachyurar

Serinus mozambicusa Camaroptera brachyurar Phyllastrephus terrestrisr

Cisticola chinianaa Phyllastrephus terrestrisr Pycnonotus barbatusr

Euplectes albonotatusa Serinus mozambicusa Apalis flavidar

Prionops plumatusb Pycnonotus barbatusr Anthreptes collarisr

Quelea queleaa Cisticola chinianaa Prionops plumatusb

Estrilda astrilda Apalis flavidar Hypargos margaritatusr

Petronia superciliarisa Anthreptes collarisr

Pytilia melbaa

apredominantly in Acacia savannabpredominantly in broadleaved woodlandrpredominantly in riverine forest

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Riverine forest, in contrast, appears to support a ratherdifferent set of species to either Acacia or broadleavedsavanna. This is supported by the fact that equal numbers ofspecies were restricted to riverine forest and Acaciasavanna. Based on comparisons of species composition ithas been argued that avian communities of riverine forest inSwaziland are derived from afromontane forest and lowlandforest, as well as from neighbouring savanna-woodland(Monadjem 2003). Because of the linear nature of rivers anddrainage lines, riverine forest is typically narrow and extendsacross geographical elevations. Riverine forest, therefore,acts as a refuge for forest species not occurring elsewherein the low-lying regions of Swaziland. These forest speciesare able to penetrate deep into savanna-woodland habitatsby following river courses and drainage lines (Oatley andArnott 1998).

The three habitats differed considerably and consistentlyin their physiognomy, but they also supported differentspecies of plants. It is not possible, based on the results ofthis study, to differentiate between the effects of vegetationstructure and composition on bird distributions. Vegetationcover, per se, did not seem to be related to avian communitystructure. However, the structural diversity of the vegetationappeared to be correlated with bird diversity. Acaciasavanna supported the highest number of bird species andalso exhibited the highest structural diversity of itsvegetation. In contrast, broadleaved woodland had thelowest structural diversity of its vegetation and supported thefewest species. This relationship between vegetationstructure and bird diversity has been reported from a widerange of habitats and geographic regions (Wilson 1974,Herremans 1993), and presumably reflects the increasedvariety of potential niches available in a more structurallydiverse habitat (Begon et al. 1986).

Although many of the correlations between speciesdensity and vegetation structure make sense with respect tothe habitats selected by these birds, some of the correlationsare unlikely to be biologically meaningful. For example, thedensity of Melaenornis pammelaina was positivelycorrelated with grass cover below 0.25m. Since this bird ispredominantly arboreal, this relationship is probablyspurious, as is the negative relationship between the highlyarboreal Dryoscopus cubla and Lybius torquata and grasscover below 0.25m. In fact, possibly only three of thecorrelations involving grass cover are biologicallymeaningful. The species involved are Francolinussephaena, Cisticola chiniana and Uraeginthus angolensis.All three species are either terrestrial or predominantlyterrestrial, and the correlations suggest that all three speciesprefer tall, dense grass cover.

Most of the correlations between bird densities and thecover of thickets or trees are not unexpected. Speciesexhibiting positive associations are generally riparian orforest species (e.g. Tauraco porphyreolophus, Apalis flavidaand Laniarius ferrugineus) (Parker 1999, Symes et al. 2000)while those exhibiting negative associations prefer moreopen savanna habitats (e.g. Melaenornis pallidus, Laniuscollurio, Tchagra australis) (Maclean 1993, Herremans1997, Harris and Franklin 2000).

A total of 216 species of birds was recorded by Parker(1994a) as occurring in terrestrial habitats in the lowveld of

Swaziland (excluding vagrants and nocturnal species).Hence, the 161 species recorded in this study constitute75% of all birds that could potentially have been recorded. Atleast half of the 55 overlooked species are low-densityspecies (such as raptors), suggesting that the three habitatsidentified in this study adequately describe the avifauna ofthe low-lying savannas of Swaziland. However, a number ofthe overlooked species (e.g. Vanellus lugubris, Coraciascaudata, Corvinella melanoleuca, Lamprotornis australis)are associated with open grassland savannas (Maclean1993) that are restricted or absent in protected areas or incommercial cattle ranches in Swaziland (Parker 1994b).Such open habitats are far more abundant on communally-owned Swazi Nation Land (SNL) where trees and shrubsare harvested for fuelwood, but SNL was not included in thisstudy. Avian diversity is generally low on SNL, where highlymobile granivorous species predominate (Monadjem 2000).The latter species are probably exploiting a seasonallyrestricted but superabundant food source in cultivated andfallow fields. The relationship between avifaunas of SNL andprotected areas in the low-lying areas of Swaziland requiresfurther investigation.

Acknowledgements — I thank the Research Board of the Universityof Swaziland for funding this study. I am most grateful to thefollowing persons for allowing me access to their properties: JHarding (Dinedor Ranch), A Howland (IYSIS Ranch), RC Boycott(Acting Director of Parks, Swaziland National Trust Commission), KRoques (Senior Warden, Mlawula Nature Reserve), T and M Reilly(Mkhaya Game Reserve and Hlane Royal National Park), B Forbes(Nisela Safaris) and D Ducasse (Mhlosinga Nature Reserve).

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Appendix 1: Bird species densities in the three habitats: Acacia savanna, broadleaved woodland and riverine forest. The • symbol indicatesthat the species was observed but a density estimate was not possible. Species names follow Maclean (1993)

Population density (birds/100 ha)Species Acacia Broadleaved RiverineButorides striatus – – •Scopus umbretta – – •Bostrychia hagedash • – •Gyps africanus • – –Torgos tracheliotus • – –Milvus migrans • – –Elanus caeruleus 1.5 • –Aviceda cuculoides – – •Aquila wahlbergi • – –Lophaetus occipitalis • – –Stephanoaetus coronatus – – •Circaetus cinereus • – –Terathopius ecaudatus • – –Haliaeetus vocifer • – –Accipiter minullus 0.6 – 0.8Accipiter badius 0.7 0.8 0.8Accipiter tachiro 2.1 • 1.7Micronisus gabar 0.6 – –Polyboroides typus 0.6 – •Falco subbuteo 1.3 – –Francolinus sephaena 6.7 1.2 •Numida meleagris 17.3 – –Guttera pucherani – – •Eupodotis ruficrista 0.6 – –Eupodotis melanogaster 0.6 • –Burhinus capensis 1.3 – –Rhinoptilus chalcopterus 1.3 – –Streptopelia semitorquata 4 4.8 2.5Streptopelia capicola 41.9 40.3 0.8Streptopelia senegalensis 12.7 1.7 –Oena capensis • – –Turtur chalcospilos 31.3 37.9 13.7Turtur tympanistria – – 2.8Treron calva 0.8 – 10.6Corythaixioides concolor • – –Tauraco porphyreolophus • 1.7 17.4Cuculus gularis 0.6 5 •Cuculus solitarius • 2.8 6.2Cuculus clamosus • – –Clamator levaillantii • – –Clamator jacobinus 0.8 – –Chrysococcyx klaas • 0.8 1.7Chrysococcyx caprius • 0.8 –Centropus superciliosus 1.7 0.8 3.3Bubo africanus – – •Cypsiurus parvus 2.1 – –Colius striatus 15.2 10.7 43.4Urocolius indicus 39 • 18Apaloderma narina – – 0.8Alcedo cristata – – •Ispidina picta – – 3.3Halcyon senegalensis 5.6 • 1.7Halcyon albiventris 1.5 18.3 29.1Halcyon chelicuti 11.9 • –Merops apiaster 0.6 – –Merops pusillus – – 0.8Upupa pops 3.3 • –Phoeniculus purpureus 18.9 17.8 14.6Rhinopomastus cyanomelas 9.6 2.5 –Tockus nasutus 1.3 – –

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Tockus alboterminatus – 1.7 3.9Tockus leucomelas 20.6 1.7 –Lybius torquatus 2.1 10.2 11.5Lybius leucomelas 0.8 – –Pogoniulus pusillus – 2 6.7Pogoniulus bilineatus – – 9.8Trachyphonus vaillantii 3.1 – –Indicator indicator 5.8 2.5 1.7Indicator minor 1.9 – –Indicator variegatus – 0.8 –Campethera abingoni 6.7 4.1 12Dendropicos fuscescens 15.2 9 3.5Thripias namaquus 2.1 3.6 –Mirafra sabota 7.7 – –Hirundo rustica 16.5 7.2 •Campephaga flava 9.6 15.7 5.9Dicrurus adsimilis 61.7 34 10.3Oriolus oriolus – – 1.7Oriolus larvatus 3.3 14.9 8.1Parus niger 39.4 41.2 29.4Anthoscopus caroli 1.9 4.2 28.2Turdoides jardineii 3.3 • –Pycnonotus barbatus 68.7 79.3 329.1Phyllastrephus terrestris 3.1 19 345.2Andropadus importunus 1.9 38.1 92.1Nicator gularis • 2.7 20.6Turdus libonyanus 17.7 20.7 18.8Cossypha heuglini • – 13.2Cossypha natalensis – – 13.3Cossypha humeralis 1.3 – 4.9Erythropygia leucophrys 39.6 45.8 26.4Erythropygia quadrivirgata – 0.8 6.5Acrocephalus palustris – – 9Phylloscopus trochilus 5.8 17.3 9.8Apalis flavida 19.8 39.5 188.6Apalis ruddi – – 7.8Sylvietta rufescens 34 16.3 8.5Eremomela icteropygialis 1.3 0.8 –Eremomela usticollis 17.3 – 2.4Camaroptera brachyura 4.6 33 361.2Calamonastes stierlingi 1.3 2.9 –Cisticola chiniana 232.9 17.5 24.6Cisticola erythrops – – 26Cisticola fulvicapilla – 2.8 –Prinia subflava 13.3 – 123.1Muscicapa striata 13.1 22.2 26.2Muscicapa adusta – – 5.2Muscicapa caerulescens – 1.7 31.9Myioparus plumbeus 0.6 • 7.9Melaenornis pammelaina 37.7 16.7 4.9Bradornis pallidus 30.8 0.8 –Sigelus silens 0.6 – –Batis molitor 78.1 40.2 16.6Terpsiphone viridis 10.2 45.5 40.1Motacilla agiump – – 1.7Anthus caffer 0.8 13.2 –Macronyx croceus – 0.8 –Lanius collurio 27.3 0.8 2.5Laniarius ferrugineus 0.6 40.3 30.2Dryoscopus cubla 13.1 39.8 62.2Nilaus afer 17.1 1.7 –Tchagra australis 11.7 6.7 1.7Tchagra senegala 6.7 4.3 –Telephorus quadricolor 0.6 2 18.8Telephorus sulfureopectus 2.7 5.3 7.1

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Malaconotus blanchoti 5.2 11.9 4.9Prionops plumatus 35.8 108.5 13.9Prionops retzii – – 21.3Cinnyricinclus leucogaster 12.9 8.3 2.5Lamprotornis australis • – –Lamprotornis nitens 31 21.2 •Buphagus erythrorhynchus 24.6 • –Nectarinia mariquensis 7.9 – 11.5Nectarinia talatala 71.9 88.3 87.3Nectarinia senegalensis 14.4 11.6 3.3Anthreptes collaris • 11.4 134.7Zosterops pallidus – 9.7 31.9Passer griseus 12.7 – –Petronia superciliaris 54.8 8.3 –Amblyospiza albifrons – – 7.4Ploceus ocularis 4.2 – 19.8Ploceus cucullatus 18.5 29.7 13.1Ploceus velatus 6.5 1.7 1.6Ploceus subaureus – – 2.4Anaplectes rubriceps 1.3 4.9 –Quelea quelea 67.5 – –Euplectes albonotatus 122.5 – –Pytilia melba 52.5 1.7 –Mandingoa nitidula – – 0.8Hypargos margaritatus – 6.6 84.9Lagonosticta rubricata 24.6 1.7 14.7Lagonosticta rhodopareia 3.1 1.7 –Lagonosticta senegala 8.1 1.7 –Uraeginthus angolensis 372.9 15 1.7Estrilda astrild 57.5 – 2.4Sporaeginthus subflavus 9.4 – –Vidua paradisea 1.3 – –Vidua funerea 0.6 – –Serinus mozambicus 357.7 21.4 3.3Emberiza flaviventris 12.7 12.1 3.5

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Appendix 2: Pearson’s correlation co-efficients for bird densities and vegetation features. Species recorded at fewer than four sites havebeen excluded from the analysis. Only significant correlations (P < 0.05) are presented. For explanation of the vegetation features see Table1 and the text

Species Grass 1 Grass 2 Tree 1 Tree 2 Tree 3 Tree 4Francolinus sephaena 0.729 -0.712 -0.662Streptopelia capicola -0.747 -0.851Tauraco porphyreolophus 0.87 0.773Cuculus solitarius 0.828Halcyon albiventris 0.656 0.85Lybius torquatus -0.656 0.69Dendropicos fuscescens -0.805 -0.723Hirundo rustica -0.768Dicrurus adsimilis -0.764 -0.706 -0.89 -0.643Oriolus larvatus -0.687 0.643Pycnonotus barbatus 0.836 0.828Phyllastrephus terrestris 0.818 0.89Andropadus importunus 0.754 0.639Nicator gularis 0.653 0.685Apalis flavida 0.78 0.833Sylvietta rufescens -0.871Camaroptera brachyura 0.831 0.879Cisticola chiniana 0.632 -0.82 -0.793 -0.74Muscicapa striata 0.701Muscicapa caerulescens 0.737 0.752Melaenornis pammelaina 0.663Bradornis pallidus -0.655 -0.776Batis molitor -0.651 -0.659Terpsiphone viridis -0.781Lanius collurio -0.709 -0.71Laniarius ferrugineus 0.647Dryoscopus cubla -0.673 0.782Nilaus afer 0.661 -0.686 -0.68Tchagra australis -0.776 -0.659Telephorus quadricolor 0.84 0.777Anthreptes collaris 0.831 0.85Zosterops pallidus 0.658 0.693 0.674Ploceus ocularis 0.719Ploceus velatus -0.633Euplectes albonotatus -0.756 -0.86 -0.653Hypargos margaritatus 0.838 0.726Uraeginthus angolensis 0.711 -0.76 -0.686 -0.637

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