Bird Community Composition Research Articles

Temporal dynamics of bird community composition: an analysis of baseline conditions from long-term data.

Numerous anthropogenic activities threaten the biodiversity found on earth. Because all ecological communities constantly experience temporal turnover due to natural processes, it is important to distinguish between change due to anthropogenic impact and the underlying natural rate of change. In this study, we used data sets on breeding bird communities that covered at least 20 consecutive years, from a variety of terrestrial ecosystems, to address two main questions. (1) How fast does the composition of bird communities change over time, and can we identify a baseline of natural change that distinguishes primeval systems from systems experiencing varying degrees of human impact? (2) How do patterns of temporal variation in composition vary among bird communities in ecosystems with different anthropogenic impacts? Time lag analysis (TLA) showed a pattern of increasing rate of temporal compositional change from large-scale primeval systems to disturbed and protected systems to distinctly successional systems. TLA slopes of <0.04 were typical for breeding bird communities with natural turnover, while communities subjected to anthropogenic impact were characterised by TLA slopes of >0.04. Most of the temporal variability of breeding bird communities was explained by slow changes occurring over decades, regardless of the intensity of human impact. In most of the time series, medium- and short-wave periodicity was not detected, with the exception of breeding bird communities subjected to periodic pulses (e.g. caterpillar outbreaks causing food resource peaks).

How High Nature Value (HNV) farmland is related to bird diversity in agro-ecosystems – Towards a versatile tool for biodiversity monitoring and conservation planning

Within the European Union, national approaches of a ‘High Nature Value (HNV) farmland’ indicator have been developed to inform about the potential of agricultural landscapes to maintain biodiversity. We assessed how bird species abundance, richness and community composition, particularly of specialist species, were associated with the German HNV farmland indicator as an area-based aggregate and with its particular components which were semi-natural landscape elements and agricultural patches with characteristic plant species mapped in representative sample plots.The aggregated HNV indicator score showed a weak but positive relationship with generalist bird species only, while specialist species were associated with individual HNV farmland features characterizing wet grasslands and open farmland. Bird community analysis revealed three groups of HNV farmland features representative of particular landscape types: (1) complex landscapes with vertical woody structures such as hedgerows or small woodlands, (2) wet grasslands and (3) open agricultural land of low land-use intensity. Large portions of unexplained variance, however, indicated that the small-scaled HNV farmland features recorded without considering the landscape context may not have fully captured all important drivers of bird diversity in agricultural landscapes.To achieve a better representation of habitat requirements particularly of specialist bird species we propose surveying HNV farmland in a landscape context and calculating landscape-specific scores for highly structured, wetland-dominated and open landscapes of low land-use intensity. As compared to the aggregated indicator, the small-scale HNV farmland survey data would more efficiently enfold its potential for tailoring conservation schemes specifically to a given landscape type and its associated bird species.

The width and biotic integrity of riparian forests affect richness, abundance, and composition of bird communities

In riparian forests, width contributes most importantly to maximizing diversity. Therefore, corridors with different widths should differ in richness, abundance, and composition. We tested this hypothesis for the bird communities of two forests on the Upper Paraná River floodplain, Paraná, Brazil. Richness and abundance were higher in riparian forest with mean width of 50 m in each margin and lower anthropogenic disturbance. Species diversity increased 30%, with increase in total width from 40 m to 100 m on average. Bird species composition also differed, and groups with the strictest ecological requirements were better represented in the wider, better-preserved forest. This indicates that conservation of riparian forests has a positive effect on their bird communities. We suggest that these environments are prioritized for recuperation, and that a 50 m width on each side of a stream is necessary for riparian forests to effectively fulfill their function in the landscape. We also note that the recently discussed Brazilian Forest Code does not conform to this requirement. © 2014 Associação Brasileira de Ciência Ecológica e Conservação. Published by Elsevier Editora Ltda.

A bird’s-eye view of forest restoration: Do changes reflect success?

To understand the ecological effects of forest restoration treatments on several old-growth forest stands in the Flathead National Forest of western Montana, USA, we surveyed birds at 72 points in treatment and control stands, and at more than 50 points in each of five potential reference stand conditions. We used a Before–After/Control-Impact design to assess treatment effects based on data collected 3years before and 2years after treatment. We also examined the similarity in bird community composition among all stand types by using a nonmetric multidimensional scaling approach. Relative abundances of only a few bird species changed significantly as a result of restoration treatments, and these changes were characterized largely by declines in the abundances of a few species associated with more mesic, dense-forest conditions, and not by increases in the abundances of species associated with more xeric, old-growth reference stand conditions. Thus, bird communities in treated stands were more similar to those in untreated stands of the same forest type than to those found in any of the potential old-growth reference stands. Although more time may be required for some bird species to respond to treatments, our results suggest that treatment plot sizes were either too small to affect bird communities or that the forest type selected for treatment was not within the range of forest types that are well suited for this type of forest restoration.

Bird conservation values of off-reserve forests in lowland Nepal

Although protected areas are central to global biodiversity conservation, off-reserve forests are increasingly recognized as potentially important for the long term conservation of biota, particularly in less-developed countries where communities rely directly on resources from natural areas. We assessed the conservation value of differently managed forests for birds in lowland tropical forests of Nepal. In particular, we explored whether their conservation value was additional or complementary to those of formal protected areas. Using data collected from 112 sites in protected areas (n=31), state managed forests (n=37) and community managed forests (n=44), we assessed how bird species richness, abundance, diversity and community composition varied among tenures. Although sites in protected areas had the greatest species diversity, community managed forests supported a complementary assemblage. Of 124 species recorded, only 45% were common to all management tenures. Overall, the distinctiveness and richness of species in sites in forests outside of protected areas contributed substantially to regional avifaunal diversity. These results highlight the potentially critical role of appropriately managed community forests. The maintenance of diverse bird assemblages in forest regions depends on complementary management of forests both outside and inside the established protected areas.

Is the effect of farming practices on songbird communities landscape dependent? A case study of olive groves in southern Spain

Extensive farming practices and landscape heterogeneity promote biodiversity in agroecosystems. However, the effect of such practices might be landscape dependent; specifically, the effect might be greatest where the loss of heterogeneity has been the largest. In recent decades, agricultural intensification and landscape simplification have dramatically affected the Mediterranean region, where olive groves are one of the predominant crops. For instance, in Spain from 1996 to 2008, the amount of land dedicated to olive groves increased by 300,000 ha (12 %). In conventional olive farming, herbicides are applied intensively to minimize competition between crops and swards for water; however, to prevent erosion, many farmers are maintaining swards within crops. This practice likely benefits farmland biodiversity, although the heterogeneity of the surrounding landscape might influence the extent of these effects. This study assessed the effects of herbaceous cover on the abundance and species richness of songbird communities in six matched pairs of olive groves (ground cover or bare ground) in homogeneous and heterogeneous landscapes over a 3-year period. We predicted that (1) the presence of ground cover and landscape heterogeneity would have a positive effect on songbird communities, and (2) the effect would be greatest in homogeneous environments. Although bird community composition differed among landscape types and farming practices in the olive groves in southern Spain, the effect of ground cover was not landscape dependent. The presence of ground cover had a positive effect on the abundance and richness of songbirds, including sensitive species, but landscape heterogeneity did not have an effect. This study underscores the important role of agricultural practices in preserving farmland bird communities, while it also suggests that landscape heterogeneity might not be very important in Mediterranean perennial farming systems. The positive effects of ground cover can be important for preserving the wintering quarters of numerous European bird species, including species of conservation concern.

Multi-scale sampling boosts inferences from beta diversity patterns in coastal forests of South Africa

Aim We used a hierarchical fractal-based sampling design to test how sampling grain influences (1) beta diversity of and (2) inferences from the modelled contribution of niche- versus dispersal-based assembly processes in structuring tree and bird assemblages. Location Coastal forest fragments, South Africa. Methods We surveyed 103 tree plots and 267 bird points within eight forest fragments and partitioned beta diversity (βsor) into its turnover (βsim) and nestedness (βnes) components. We evaluated how sampling at fine, intermediate and coarse scales influenced beta diversity components, and compared how tree and bird beta diversity responded to sampling grain variation. We then explored the relative contributions of niche- and dispersal-based assembly processes in explaining spatial turnover as a function of sampling grain and/or study taxon, by using multiple regression modelling on distance matrices and variance partitioning. Results The βsor of trees and birds was mainly explained by βsim at all sampling scales. For both taxonomic groups, βsor and βsim decreased as sampling scale increased. Beta diversity differed among trees and birds at fine, but not at coarse, sampling scales. Dispersal-based assembly processes were the best predictors of community assembly at fine scales, whereas niche-based assembly processes were the best predictors at coarse scales. However, most of the variation in tree community composition was explained at fine scales (by dispersal-based assembly processes), while most of the variation in bird community composition was explained at coarse scales (by niche-based assembly processes). Main conclusions Our study shows that inferences from beta diversity are scale dependent. By matching the grain of the data with the grain at which predictor variables and associated processes are likely to operate, multi-scale sampling approaches can help improve planning for biodiversity conservation and should be part of initiatives aimed at ecological conservation plans.

Use of Multispecies Occupancy Models to Evaluate the Response of Bird Communities to Forest Degradation Associated with Logging

Forest degradation is arguably the greatest threat to biodiversity, ecosystem services, and rural livelihoods. Therefore, increasing understanding of how organisms respond to degradation is essential for management and conservation planning. We were motivated by the need for rapid and practical analytical tools to assess the influence of management and degradation on biodiversity and system state in areas subject to rapid environmental change. We compared bird community composition and size in managed (ejido, i.e., communally owned lands) and unmanaged (national park) forests in the Sierra Tarahumara region, Mexico, using multispecies occupancy models and data from a 2-year breeding bird survey. Unmanaged sites had on average higher species occupancy and richness than managed sites. Most species were present in low numbers as indicated by lower values of detection and occupancy associated with logging-induced degradation. Less than 10% of species had occupancy probabilities >0.5, and degradation had no positive effects on occupancy. The estimated metacommunity size of 125 exceeded previous estimates for the region, and sites with mature trees and uneven-aged forest stand characteristics contained the highest species richness. Higher estimation uncertainty and decreases in richness and occupancy for all species, including habitat generalists, were associated with degraded young, even-aged stands. Our findings show that multispecies occupancy methods provide tractable measures of biodiversity and system state and valuable decision support for landholders and managers. These techniques can be used to rapidly address gaps in biodiversity information, threats to biodiversity, and vulnerabilities of species of interest on a landscape level, even in degraded or fast-changing environments. Moreover, such tools may be particularly relevant in the assessment of species richness and distribution in a wide array of habitats.

How do edge effect and tree species diversity change bird diversity and avian nest survival in Germany’s largest deciduous forest?

Habitat fragmentation is a major driver of species loss. Here we test the hypotheses that high tree diversity in a large deciduous forest enhances bird diversity and nest survival. We further expect that forest edges support higher bird diversity when different habitat types adjoin, whereas nest predation is not higher, because the large forest area mitigates potential edge effects. We studied how edge-centre differences and tree diversity (beech-dominated vs. tree-species rich) affect the bird community and survival rates of ground breeding birds’ nests based on an artificial nest predation experiment in the Hainich National Park, Germany. We surveyed birds three times during the breeding season. We selected six forest stands with low tree diversity (i.e. dominated by beech) and six with high tree diversity (i.e. tree-species rich). Each forest stand contained four bird survey plots (plot 1: 0–30m, plot 2: 60–90m, plot 3: 120–150m and plot 4: 180–210m distant from edge; altogether 48 bird survey plots). Additionally each plot corner contained one artificial ground nest baited with one Blue-breasted Quail egg and one plasticine egg for eight days of exposure in the middle of the breeding season. Bird abundance and diversity were higher in the first 30m of the forest. Bird diversity, including ground breeding birds, was also enhanced by higher percentages of bushes, which can provide enhanced food supply, perches as well as sheltering. Nest predation showed no edge effect, supporting the idea that small area of forest fragments causes more important negative effects than the edge in large forest remnants. Predation rates were higher in tree-species rich stands compared to beech-dominated stands, probably due to greater diversity and density of mammalian predators. Edge effects shaped the bird community composition and positively affected abundances of tree and shrub breeding birds, but did not affect ground breeders and the nest predation of ground nests. Shrub breeders accumulating in forest edges might, however, suffer more from nest predation in forest fragments. In conclusion, bird diversity and avian egg predation were affected by both forest edges and tree diversity in surprisingly different ways.

Impact of Phytophthora-dieback on birds in Banksia woodlands in south west Western Australia

Invasive plant pathogens have impacted forest and woodland systems globally and can negatively impact biodiversity. The soil-borne plant pathogen Phytophthora cinnamomi is listed as one of the world’s worst invasive species and alters plant community composition and habitat structure. Few studies have examined how these Phytophthora-induced habitat changes affect faunal communities. We examined bird communities in Banksia woodland with, and without, Phytophthora dieback in a biodiversity hotspot, southwestern Australia. Seven sites along dieback fronts, with paired 1-ha plots in diseased and healthy vegetation, were surveyed monthly for birds over seven months. Vegetation assessments showed that diseased sites had reduced plant species richness, litter, shrub, tree and canopy cover, high bare ground and significantly lower flowering scores, than healthy sites. Bird community composition differed significantly between diseased and healthy sites, although total bird abundance, total species richness and foraging guilds, did not. Average species richness of birds per survey and the abundance of brown honeyeaters, western spinebills and silvereyes was lower in diseased than healthy sites. The tawny-crowned honeyeater had higher abundances in diseased sites. Similarity matrices of habitat structure, flowering scores and bird assemblages were congruent, indicating that habitat structural differences were influencing bird community composition. Our results suggest that this pathogen is potentially a serious threat to avian biodiversity and especially for nectarivores, and populations in fragmented landscapes. Since elimination of the pathogen is not currently possible, management should focus on methods of preventing its spread until techniques to eliminate the pathogen are developed.

Effects of fire disturbance on bird communities and species of mountain Serrano forest in central Argentina

In central Argentina, Serrano forest has a long history of fire disturbance; however, the impact of fire on avifauna remains unknown. We compared the avian–habitat relationships in forest patches with low, moderate, and high fire regimes using a community-level (species richness, abundance, ordination and guilds) and species-level (indicator species analysis) approach. In patches under each fire condition, we recorded bird community composition, richness and abundance, and different vegetation structure variables. The site under high-severity fire regime was structurally poor and had been converted from original forest to dense grassland. There, diversity of bird community was low, retaining approximately 30 % of the species present in the least impacted site. Avian assemblage was dominated by generalist and open area birds. Guilds were underrepresented, showing an important reduction of foliage granivorous, nectarivorous, omnivores, and foliage and bark insectivorous, and absence of fly-catchers. Moreover, low abundance of forest understory, midstory, and canopy species and of birds belonging to open and closed nesting guilds was detected. By contrast, under low and moderate-severity fire regimes highest bird diversity as well as highest representativeness of most guilds was observed. Forest bird species were strongly associated with low fire disturbance, whereas moderate fire disturbance was characterized by the presence of forest and generalist species. Given the critical conservation status of Serrano forest in Córdoba, Argentina, habitat restoration and protection of forest relicts could be suitable measures to promote avifauna preservation.

The value of plantation forests for plant, invertebrate and bird diversity and the potential for cross-taxon surrogacy

As the area of plantation forest expands worldwide and natural, unmanaged forests decline there is much interest in the potential for planted forests to provide habitat for biodiversity. In regions where little semi-natural woodland remains, the biodiversity supported by forest plantations, typically non-native conifers, may be particularly important. Few studies provide detailed comparisons between the species diversity of native woodlands which are being depleted and non-native plantation forests, which are now expanding, based on data collected from multiple taxa in the same study sites. Here we compare the species diversity and community composition of plants, invertebrates and birds in Sitka spruce- (Picea sitchensis-) dominated and Norway spruce- (Picea abies-) dominated plantations, which have expanded significantly in recent decades in the study area in Ireland, with that of oak- and ash-dominated semi-natural woodlands in the same area. The results show that species richness in spruce plantations can be as high as semi-natural woodlands, but that the two forest types support different assemblages of species. In areas where non-native conifer plantations are the principle forest type, their role in the provision of habitat for biodiversity conservation should not be overlooked. Appropriate management should target the introduction of semi-natural woodland characteristics, and on the extension of existing semi-natural woodlands to maintain and enhance forest species diversity. Our data show that although some relatively easily surveyed groups, such as vascular plants and birds, were congruent with many of the other taxa when looking across all study sites, the similarities in response were not strong enough to warrant use of these taxa as surrogates of the others. In order to capture a wide range of biotic variation, assessments of forest biodiversity should either encompass several taxonomic groups, or rely on the use of indicators of diversity that are not species based.

Restoration Practices Have Positive Effects on Breeding Bird Species of Concern in the Chihuahuan Desert.

Woody plant encroachment into grasslands is a global concern. Efforts to restore grasslands often assume that removal of woody plants benefits biodiversity but assumptions are rarely tested. In the Chihuahuan Desert of the Southwestern United States, we tested whether abundances of grassland specialist bird species would be greater in plant communities resulting from treatment with herbicides to remove encroaching shrubs compared with untreated shrub‐dominated areas that represented pre‐treatment conditions. In 2010, we surveyed breeding birds and vegetation at 16 treated–untreated pairs. In 2011, we expanded the survey effort to 21 treated–untreated pairs, seven unpaired treatment areas, and five reference grassland areas. Vegetation in treatment areas had higher perennial grass foliar and basal cover and lower shrub foliar cover compared with untreated areas. Several regionally declining grassland specialists exhibited higher occurrence and relative abundance in treated areas. A shrubland specialist, however, was associated with untreated areas and may be negatively impacted by shrub removal. Bird community composition differed between treated and untreated areas in both years. Our results indicate that shrub removal can have positive effects on grassland specialist bird species, but that a mosaic of treated and untreated areas might be most beneficial for regional biodiversity.

Regrowth provides complementary habitat for woodland birds of conservation concern in a regenerating agricultural landscape

Farmland abandonment often leads to an increase in vegetation cover in formerly cleared landscapes. In regions where forests and woodlands were cleared for agriculture, regrowth could be an effective way to increase species diversity by re-constructing a variegated landscape. Our study investigated the conservation outcomes for birds across a regenerating agricultural landscape. We compared bird composition across a range of land use and gradient of vegetation cover from cleared pasture, through regrowth sites of varying structure, to remnant forests. Bird community composition differed significantly among vegetation classes, with regrowth providing habitat for a complementary group of high conservation value species, rather than simply providing extra habitat for species that were otherwise well represented in the region. Variations in bird community composition were best explained by site variables that contributed to vegetation structure and internal patch variation. Regrowth had a higher diversity of cover than forest or pasture, and this created habitat for many woodland bird species. Regrowth vegetation may be slower to proceed, but it has the potential to complement active revegetation activities in adjacent production areas and enhance connectivity between remnant forest patches. While the benefits of regrowth are context specific, where regrowth improves landscape heterogeneity, there is great potential for conservation gains for birds.

Assessing the regional impacts of increased energy maize cultivation on farmland birds

The increasing cultivation of energy crops in Germany substantially affects the habitat function of agricultural landscapes. Precise ex ante evaluations regarding the impacts of this cultivation on farmland bird populations are rare. The objective of this paper was to implement a methodology to assess the regional impacts of increasing energy maize cultivation on the habitat quality of agricultural lands for farmland birds. We selected five farmland bird indicator species with varying habitat demands. Using a crop suitability modelling approach, we analysed the availability of potential habitat areas according to different land use scenarios for a real landscape in Northeast Germany. The model was based on crop architecture, cultivation period, and landscape preconditions. Our results showed that the habitat suitability of different crops varied between bird species, and scenario calculations revealed an increase and a decrease in the size of the potential breeding and feeding habitats, respectively. The effects observed in scenario 1 (increased energy maize by 15%) were not reproduced in all cases in scenario 2 (increased energy maize by 30%). Spatial aggregation of energy maize resulted in a negative effect for some species. Changes in the composition of the farmland bird communities, the negative effects on farmland bird species limited in distribution and spread and the relevance of the type of agricultural land use being replaced by energy crops are also discussed. In conclusion, we suggest a trade-off between biodiversity and energy targets by identifying biodiversity-friendly energy cropping systems.

Effects of landscape, land use and vegetation on bird community composition and diversity in Inner Anatolian steppes

We present here the first systematic study on drivers of bird community composition and diversity in Anatolian steppes (Turkey), an environment important for populations of threatened grassland birds yet underrepresented in conservation networks. We focused on one million hectares of mountainous land with a long and varied land use history, and collected quantitative data on breeding birds as well as environmental, vegetation, landscape and land use parameters at 32 sites. Data were analyzed by canonical correspondence analysis (CCA) and hierarchical partitioning to understand avian community structure and reveal major drivers of observed patterns. Bird communities in high-altitude steppes of inner Turkey showed patterns in species richness and community composition that were best explained by an altitudinal gradient and by human activities. Steppe birds occurred most often in cropland abandoned 20–50 years ago with good coverage of erect leafy plants while overall avian diversity tended to increase with reduced grazing pressure and with nearby presence of rural settlements. CCA results revealed a contrast between highly heterogeneous anthropogenic environments in warmer and drier land with woody elements, and treeless steppes at higher elevations that were, apart from transhumant grazing, little influenced by human activities. The former sites were characterized by the occurrence of several grassland birds along with a variety of generalist species, some of which required the presence of trees, while the latter sites were less diverse but usually with a higher proportion of steppe-dependent birds in their composition. To conserve steppes for birds, we recommend as key actions to maintain the current landscape mosaic, sustain low to moderate grazing levels and use our findings in developing a network of protected areas.

Landscape-Scale Disturbances Modified Bird Community Dynamics in Successional Forest Environment

Ecosystem-based forest management strives to develop silvicultural practices that best emulate natural disturbances such as wildfire to conserve biodiversity representative of natural forest ecosystems. Yet, current logging practices alter forest structure and reduce the proportion of old-growth forest and, consequently, can exert long-term effects on the dynamics of forest biota. The stand- and landscape-scale factors driving bird community dynamics in post-disturbance environment remain poorly understood. In this study, we examined bird community dynamics along successional gradients in boreal ecosystems originating from fire and logging in landscapes dominated by old-growth forest. We tested if bird species richness and community compositions in clear-cutting stands became comparable to those in natural stands after 70 years, and identified the relative contributions of stand- and landscape-scale forest attributes in bird community dynamics. Based on records of bird occurrences at 185 field sites in natural and clearcutting stands, we demonstrate that (1) both forest structures and bird communities underwent evident changes along successional gradients in post-clearcutting environment; (2) bird species richness and community composition in 60- to 70-years-old clearcutting stands still differed from those in 50- to 79-years-old natural stands, in spite of the fact that most forest attributes of clearcutting stands became comparable to those of natural stands after 40 years; and (3) landscape disturbances contributed more than stand characteristics in explaining the lack of convergence of mature forest species, residents, and short-distance migrants in post-clearcutting environment. Our study points out that more regards should be paid to improve the landscape configuration of the managed forests, and implies that old-growth forest retention within logged areas, combined with selection cutting and prolonged logging rotations, can better emulate fire and alleviate forest harvesting effects on bird community assemblages typical of natural boreal ecosystem.

Changes of community composition at multiple trophic levels due to hunting in Nigerian tropical forests

Hunting in tropical forests decimates large mammals, and this may have direct and indirect effects on other trophic levels and lead to trophic cascades. We compared replicated sites of hunted and protected forests in southeastern Nigeria, with respect to community composition of primates, other mammals, birds, plant seedlings, and mature trees. We make predictions regarding the community composition at the different trophic levels. In forests where large primates are rare, we hypothesize that their ecological role will not be fully compensated for by small frugivores. We apply multivariate methods to assess changes in community composition of mammals, birds, and seedlings, controlling for any differences between sites in the other groups, including mature trees. Medium and large (4–180 kg) primates were much rarer in hunted sites, while porcupine and rock hyrax increased in abundance with hunting. In contrast, the community composition of birds was similar in both types of forests. Seedling communities were significantly related to the community composition of mammals, and thus strongly affected by hunting. In protected forests primate dispersed plant seedling species dominated, whereas in hunted forests the seedling community was shifted towards one dominated by abiotically dispersed species. This was probably both a consequence of reduced seed dispersal by primates, and increased seed predation by rodents and hyrax. Hence we found no evidence for buffering effects on tree regeneration through functional compensation by non‐hunted animals (such as birds). Our results highlight how seedling communities are changed by the complex plant–animal intera ctions, triggered by the loss of seed dispersers. The results predict a rarity of primate‐dispersed trees in future tropical forest canopies; a forest less diverse in timber and non‐timber resources.

Vegetation composition and structure influences bird species community assemblages in the highland agricultural landscape of Nyandarua, Kenya

We examined the effects of vegetation composition and structure on bird species diversity and richness of foraging guilds in the highland agricultural landscape of Nyandarua, Kenya. Bird point counts and vegetation surveys were undertaken during four sampling periods. Linear mixed models were used to examine the effects of vegetation variables on bird species diversity and richness of respective foraging guilds, and logistic generalised linear models used to examine vegetation effects on the presence/absence of the 17 most common bird species. Bird species diversity increased with increasing density of woody plant species and vegetation structural heterogeneity. Two gradients of increasing vegetation structural heterogeneity were most important in influencing bird community composition and had positive effects on species diversity and the presence of most of the species assessed: (1) increasing closed cover due to woody plant density, which also had positive effects on species richness of frugivores and nectarivores, but negative effects on carnivores, and (2) increasing fallow and cultivation versus decreasing grassland/pasture cover, which also had a positive effect on species richness of granivores and omnivores. This study reaffirms the need to maintain a structurally rich agricultural landscape for it to support agrobiodiversity.

Effectiveness of eucalypt plantations as a surrogate habitat for birds

In the fragmented forest landscape of Europe, tree plantations comprise an increasingly important fraction of the matrix surrounding natural forest fragments. Plantations may provide habitat for forest biodiversity, which may enhance landscape connectivity and regional biodiversity. I compared the diversity and composition of bird communities in eucalypt plantations of three ages (young, intermediate and mature) and with low management intensity with respect to pine plantations, native forests and shrublands. Differences in composition of species and species groups were analyzed with PERMANOVA and visually represented using NMDS ordinations. Species groups were established according to diet, habitat and microhabitat preferences, and conservation status. A total of 887 bird encounters and 45 species were recorded. Native forests had the highest species richness per site and per sample, followed by pine plantations and shrublands. Eucalypt plantations had the lowest species richness, and decreasing with age, and the lowest bird abundance. According to composition, two habitat groups could be distinguished: wooded habitats, including native forests and plantations except young eucalypt plantations; and shrubby habitats, with shrublands and young eucalypt plantations. Native forests and pine plantations had the most similar composition among wooded habitats, and were associated with forest specialists, whereas species having unfavorable conservation status were associated with shrublands and young eucalypt plantations. In eucalypt plantations, birds were mainly associated with shrubs at young ages and with canopies at older ages, with flowers as an important food resource. The paucity of birds in eucalypt plantations contrasted with the diverse and abundant avifauna in pine plantations. The alien status and taxonomic isolation of Eucalyptus globulus in the region, together with specific features of its leaves and bark, may explain the low suitability of eucalypt plantations, by limiting the presence of phytophagous insects and thus the availability of prey for birds.