Birds,Cattle, and Bracken Ferns: Bird Community Responses to a Neotropical Landscape Shaped by Cattle Grazing Activities

Large areas of tropical moist forests have been converted to cattle pastures, generating complex landscapes where different habitats are represented by small patches with an uneven spatial distribution. Here, we describe how bird communities respond to the different elements present in a livestock landscape that was originally dominated by tropical moist forest. We surveyed six habitats: open pastures, pastures with shrubs, early‐ and middle‐secondary forests, mature forest, and pastures invaded by bracken ferns (Pteridium aquilinum). Bird diversity was high in secondary and mature forests, and low in fern‐invaded sites and open pastures. Fern‐dominated sites had the lowest bird species richness, and trophic guild diversity of all habitats. Habitat structure affected both bird species richness and densities in similar ways. Tree species richness was the habitat attribute that had a bigger positive effect on bird species richness. Bird community structure varied among sampled habitats, separating habitats in two major groups (forests and pastures). Our data indicate that bracken fern‐invaded pastures were the worst habitat condition for avian communities. To increase bird diversity, we recommend to eliminate or manage bracken fern and to increase shrub and tree cover in open pastures to provide food resources and shelter for birds. Finally, we encourage the maintenance of secondary and mature forest remnants as a strategy to conserve resident birds within a landscape dominated by livestock activities.     

Landscape matrix modifies richness of plants and insects in grassland fragments

There is an increasing awareness that not only area and isolation, but also the characteristics of the landscape surrounding habitat patches influence population persistence and species diversity in fragmented landscapes. In this study, we examine the effects of grassland fragmentation and land use in the landscape matrix (on a 2 km scale) on species richness of plants, butterflies, bees and hoverflies. These organisms were studied in replicated remnant patches of different sizes and isolation, embedded in landscapes dominated either by forest, arable land or a mix of these. We found positive effects of patch area on species richness of the three insect taxa, but not of plants. Isolation had a negative effect only on hoverflies. Matrix type had contrasting effects on the studied taxa. Species richness of plants and butterflies was lowest in patches in landscapes dominated by arable land and highest in forest‐dominated landscapes. For hoverflies, the negative effect of small patch area was strongest in forest‐dominated landscapes, and there was a similar non‐significant trend for bees. Our study shows the importance of considering matrix characteristics when studying responses to habitat fragmentation. Differences in matrix response among organism groups probably impinge on differing mechanisms. A forest matrix is likely to provide additional resources for butterflies but either constitute a barrier to dispersal or deprive resources as compared to an arable matrix for hoverflies. Enhanced plant diversity in grassland patches embedded in forested landscapes can be explained by habitat generalists more easily invading these patches, or by an unpaid extinction debt in these landscapes.     

Spatial Variation of Bird Species in Landscapes Dominated by Old-growth Forests in Northern Boreal Finland

An important issue in conservation planning is to study the distribution and abundance patterns of species in natural landscapes. Information of concordant and clumped species distribution pattertns can enhance attempts to focus conservation efforts in sites/areas preferred by various species. We compared bird species abundance, community composition and species distribution patterns in three large old-growth forest areas (size 40–120 km²) in northern boreal Finland on the basis of quantitative bird censuses. Total bird density and species composition, and mean density and variances of the most abundant species were highly similar between the three areas. Most of the bird species were distributed randomly within the areas and species preferring old-growth forests showed compensatory density variation without preference for any sub-area. Mean density of species preferring old-growth forests was significantly higher in the studied large old-growth forests than in smaller old-growth forests and was about threefold higher than regional density of species in a predominantly managed landscape matrix. Bird species preferring old-growth forests are probably not dependent on a certain specific part of a virgin boreal forest landscape but rather on the overall size of the high-quality and diverse old-growth forest area.     

Bat and Bird Assemblages from Forests and Shade Cacao Plantations in Two Contrasting Landscapes in the Atlantic Forest of Southern Bahia, Brazil

In the core region of Brazilian cocoa production, shade cacao plantations (so-called cabrucas) are important components of regional landscapes, constituting potential habitat for a vast array of the regional biota. This research focuses on the ability of cabrucas to harbor bird and bat species in two nearby districts – Una and Ilhéus – with contrasting landscapes. At Una, cabrucas represent less than 6% of the land and are surrounded by large tracts of forest, whereas at Ilhéus these shade plantations are the landscape's dominant feature. Bird and bat communities were richer in cabrucas located in Una compared to nearby forest, while cabrucas from the Ilhéus landscape were significantly poorer in species than nearby forest fragments. However, bird assemblages in cabrucas were characterized by the loss of understory specialists and the increase of more open area and generalist species, whereas forest dwellers still comprised most of the bat species reported in cabrucas. Species richness and composition differed between the two landscapes. Forest fragments and cabrucas from Ilhéus harbored fewer forest-dwelling species than similar habitats in Una. Our study shows that cabrucas support high species richness of birds and bats from the native assemblages but are no surrogates for intact forests, since the presence and representativeness of some forest species apparently depends on the existence of nearby forests. A landscape dominated by cabrucas with a minor portion of native forest is unlikely to ensure long-term conservation of many target species, particularly those of major conservation concern.     

Extinction thresholds and negative responses of Afrotropical ant-following birds to forest cover loss in oil palm and agroforestry landscapes

Afrotropical ant-following birds are vulnerable to forest loss and disturbance, but critical habitat thresholds regarding their abundance and species richness in human-dominated landscapes, including industrial oil palm plantations, have never been assessed. We measured forest cover through Landsat imagery and recorded species richness and relative abundance of 20 ant-following birds in 48 plots of 1-km², covering three landscapes of Southwest Cameroon: Korup National Park, smallholder agroforestry areas (with farms embedded in forest), and an industrial oil palm plantation. We evaluated differences in encounter frequency and species richness among landscapes, and the presence of critical thresholds through enhanced adaptive regression through hinges. All species were detected in Korup National Park and the agroforestry landscape, which had similar forest cover (>85%). Only nine species were found in the oil palm plantation (forest cover = 10.3 ± 3.3%). At the 1-km² scale, the number of species and bird encounters were comparable in agroforests and the protected area: mean species richness ranged from 12.2 ± 0.6 in the park and 12.2 ± 0.6 in the agroforestry matrix to 1.0 ± 0.4 in the industrial oil palm plantation; whereas encounters decreased from 34.4 ± 3.2 to 26.1 ± 2.9 and 1.3 ± 0.4, respectively. Bird encounters decreased linearly with decreasing forest cover, down to an extinction threshold identified at 24% forest cover. Species richness declined linearly by ca. one species per 7.4% forest cover lost. We identified an extinction threshold at 52% forest cover for the most sensitive species (Criniger chloronotus, Dicrurus atripennis, and Neocossyphus poensis). Our results show that substantial proportions of forests are required to sustain complete ant-following bird assemblages in Afrotropical landscapes and confirm the high sensitivity of this bird guild to deforestation after industrial oil palm development. Securing both forest biodiversity and food production in an Afrotropical production landscape may be best attained through a combination of protected areas and wildlife-friendly agroforestry.     

Spatial variation and biogeography of sand forest avian assemblages in South Africa

Aim To examine biogeographical affiliations, habitat‐associated heterogeneity and endemism of avian assemblages in sand forest patches and the savanna‐like mixed woodland matrix. Location Two reserves in the Maputaland Centre of Endemism (MC) on the southern Mozambique Coastal Plain of northern KwaZulu‐Natal, South Africa. Methods Replicated surveys were undertaken in each of the two habitat types in each reserve, providing species abundance data over a full year. Vegetation structure at each of the survey sites was also quantified. Differences between the bird assemblages and the extent to which vegetation structure explained these differences were assessed using multi‐variate techniques. Biogeographical comparisons were based on species presence/absence data and clustering techniques. Results Bird assemblages differed significantly between habitats both within a given reserve and between reserves, and also between reserves for a given habitat. Differences in vegetation structure contributed substantially to differences between the avian assemblages. Of the four species endemic to the MC, three (Neergaard’s sunbird, Rudd’s apalis, and Woodward’s batis) were consistently present in sand forest. The fourth (pink‐throated twinspot) preferred mixed woodland. None of these endemic species was classed as rare. In the biogeographical analysis, both the sand forest and the mixed woodland bird assemblages were most similar to bird assemblages found in the forest biome or the Afromontane forest biome, depending on the biome classification used. Main conclusions The close affinities of sand forest and mixed woodland assemblages to those of the forest biome are most likely due to similarities in vegetation structure of these forests. Bird assemblages differ between the sand forest and mixed woodland habitats both within a given reserve and between reserves, and also between reserves for a given habitat. These differences extend to species endemic to the MC. Thus, conservation of sand forest habitat in a variety of areas is necessary to ensure the long‐term persistence of the biota.     

Ferns,frogs, lizards,birds and bats in forest fragments and shade cacao plantations in two contrasting landscapes in the Atlantic forest,Brazil

The traditional shade cacao plantations (cabrucas) of southern Bahia, Brazil, are biologically rich habitats, encompassing many forest-dwelling species. However, a critical question for the conservation management of this specific region, and the highly fragmented Atlantic forest in general, is to what extent the conservation value of cabrucas relies on the presence of primary forest habitat in the landscape. We investigated the relative importance of cabrucas and forests for the conservation of five diverse biological groups (ferns, frogs, lizards, birds and bats) in two contrasting landscapes in southern Bahia, one dominated by forest with some interspersed cabrucas, and one dominated by cabrucas with interspersed forest fragments. The community structure (richness, abundance and diversity) of all biological groups differed between cabrucas and forests, although these differences varied among groups. A high number of forest species was found in the cabrucas. However, there were pronounced differences between the two landscapes with regard to the ability of cabrucas to maintain species richness. Irrespective of the biological group considered, cabrucas located in the landscape with few and small forest fragments supported impoverished assemblages compared to cabrucas located in the landscape with high forest cover. This suggests that a greater extent of native forest in the landscape positively influences the species richness of cabrucas. In the landscape with few small forest fragments interspersed into extensive areas of shade cacao plantations, the beta diversity of birds was higher than in the more forested landscape, suggesting that forest specialist species that rarely ventured into cabrucas were randomly lost from the fragments. These results stress both the importance and the vulnerability of the small forest patches remaining in landscapes dominated by shade plantations. They also point to the need to preserve sufficient areas of primary habitat even in landscapes where land use practices are generally favorable to the conservation of biodiversity.     

Are protected areas maintaining bird diversity?

Evaluating the effectiveness of protected areas for sustaining biodiversity is crucial to achieving conservation outcomes. While studies of effectiveness have improved our understanding of protected‐area design and management, few investigations (< 5%) have quantified the ecological performance of reserves for conserving species. Here, we present an empirical evaluation of protected‐area effectiveness using long‐term measures of a vulnerable assemblage of species. We compare forest and woodland bird diversity in the Australian Capital Territory over 11 yr on protected and unprotected areas located in temperate eucalypt woodland and matched by key habitat attributes. We examine separately the response of birds to protected areas established prior to 1995 and after 1995 when fundamental changes were made to regional conservation policy. Bird diversity was measured in richness, occurrence of vulnerable species, individual species trajectories and functional trait groups. We found that protected areas were effective in maintaining woody vegetation cover in the study region, but were less effective in the protection of the target bird species assemblage. Protected areas were less species rich than unprotected areas, with significant declines in richness across sites protected prior to 1995. Small, specialised and vulnerable species showed stronger associations with unprotected areas than protected areas. Our findings indicate that recently established reserves (post‐1995) are performing similarly to unprotected woodland areas in terms of maintaining woodland bird diversity, and that both of these areas are more effective in the conservation of woodland bird populations than reserves established prior to 1995. We demonstrate that the conservation value of protected areas is strongly influenced by the physical characteristics, as well as the landscape context, of a given reserve and can diminish with changes in surrounding land use over time. Both protected areas and off‐reserve conservation schemes have important roles to play in securing species populations.     

Habitat quality is more important than matrix quality for bird communities in protected areas

Protected areas are meant to preserve native local communities within their boundaries, but they are not independent from their surroundings. Impoverished habitat quality in the matrix might influence the species composition within the protected areas through biotic homogenization. The aim of this study was to determine the impacts of matrix quality on species richness and trait composition of bird communities from the Finnish reserve area network and whether the communities are being subject of biotic homogenization due to the lowered quality of the landscape matrix. We used joint species distribution modeling to study how characteristics of the Finnish forest reserves and the quality of their surrounding matrix alter species and trait compositions of forest birds. The proportion of old forest within the reserves was the main factor in explaining the bird community composition, and the bird communities within the reserves did not strongly depend on the quality of the matrix. Yet, in line with the homogenization theory, the beta‐diversity within reserves embedded in low‐quality matrix was lower than that in high‐quality matrix, and the average abundance of regionally abundant species was higher. Influence of habitat quality on bird community composition was largely explained by the species' functional traits. Most importantly, the community specialization index was low, and average body size was high in areas with low proportion of old forest. We conclude that for conserving local bird communities in northern Finnish protected forests, it is currently more important to improve or maintain habitat quality within the reserves than in the surrounding matrix. Nevertheless, we found signals of bird community homogenization, and thus, activities that decrease the quality of the matrix are a threat for bird communities.     

Spatial and temporal changes in bird assemblages in forest fragments in an eastern Amazonian savannah

We investigated the effects of forest fragmentation on bird assemblages in an Amazonian savannah landscape with forest fragments that have been isolated for more than 100 years. The study was conducted in areas surrounding the village of Alter do Chão (2°31′S, 55°00′W), Santarém, Brazil. Bird surveys and measurements of tree density were undertaken in 25 areas, with 19 plots in forest fragments of different sizes and six in an area of continuous forest. Data on forest‐fragment size, perimeter, and isolation were obtained from a georeferenced satellite image. Variation in number of bird species recorded per plot was not related to vegetation structure (tree density). The number of bird species recorded per plot increased significantly only with fragment area, but was not influenced by fragment shape or degree of isolation, even when considering species from the savannah matrix in the analysis. Fragments had fewer rare species. Multivariate ordination analyses (multiple dimensional scaling, [MDS]) indicated that bird species composition changed along a gradient from small to large forest fragments and continuous‐forest areas. In the Amazonian savannah landscapes of Alter do Chão, the organization and composition of bird assemblages in forest fragments are affected by local long‐term forest‐fragmentation processes. Differences in the number of bird species recorded per plot and assemblage composition between forest fragments and continuous forest were not influenced by forest structure, suggesting that the observed patterns in species composition result from the effects of fragmentation per se rather than from preexisting differences in vegetation structure between sites. Nevertheless, despite their long history of isolation, the forest fragments still preserve a large proportion (on average 80%) of the avifauna found in continuous‐forest areas. The fragments at Alter do Chão are surrounded by natural (rather than planted) grassland, with many trees in the savannah matrix and the landscape has vast areas covered by forest, which may have helped to ameliorate the influences of forest fragmentation.     

Novel patch–matrix interactions: patch width influences matrix use by birds

This study investigated the influence of the width of patches of native eucalypt forest on bird occurrence in stands of exotic radiata pine ( Pinus radiata ) forests that surrounded such patches. Boundaries between eucalypt and pine forests were surveyed to examine bird occurrence and species richness at different distances in the pine matrix from eucalypt forest edges. Birds were counted by the area search method within 0.5 ha quadrats at 32 study sites (where sites spanned the boundaries of pine and eucalypt forests). Data were examined using generalised linear mixed models. Species richness and occurrence of particular species in quadrats located within pine forests decreased with increasing distance from eucalypt patches. This resulted, in part, from the fact that several species found in native patches also use pine plantations as additional foraging areas. Species richness decreased more quickly with distance from eucalypt patches in younger than in older pine stands. The width of native forest patches also influenced bird occurrence in adjacent pine forest matrix. Bird species richness decreased more rapidly in exotic plantations adjacent to wide rather than narrow patches of native forest. To the best of our knowledge, no studies have previously reported that dimensions of patches can influence the use of surrounding matrix. We introduce the term "halo effect" for the influence of patch attributes on the differential use of matrix adjacent to native patches. These patterns highlight that conservation efforts in patchy environments should protect not only native patches but also adjacent areas of matrix into which animals extend their home ranges.     

Structural implications of traditional agricultural landscapes on the functional diversity of birds near the Korean Demilitarized Zone

Bird assemblages are sensitive to changes in landscape composition and the environment, such as those that result from drought. In this study, the relationship between landscape composition and avian functional diversity in traditional agricultural ecosystems in the Civilian Control Zone (CCZ) of Korea was examined. In addition, the resilience of biodiversity to changes in landscape elements resulting from drought conditions was investigated. The traditional agricultural landscape (TAL) of the sites studied was divided into three types: TAL 1 had a high proportion of rice paddies, TAL 2 included large forest areas, and TAL 3 represented areas with drylands. Of these, TAL 1 showed the highest species richness and functional richness, but these measures were most vulnerable to drought. Meanwhile, TAL 2 showed that the bird communities were more tolerant under drought event. This study shows that to conserve and enhance the diversity of birds in traditional agricultural landscapes of Northeast Asia, active management of forest areas is needed to protect bird populations. In addition, commercial pressures to develop this area will require urgent biodiversity conservation plans to protect the unique biodiversity of the Korean CCZ. This study thus provides landscape management guidance for conservation planning.     

Conservation value for birds of traditionally managed isolated trees in an agricultural landscape of Madagascar

Isolated trees have distinctive economic, social and cultural value for the Betsileo people living on the edge of the protected forest corridor between Ranomafana and Andringitra national parks, in South-East Madagascar. Many of these trees are Ficus spp., traditionally protected and respected. At the landscape level, they are isolated features in a heterogeneous mosaic, providing fruit, shade and aesthetic services in open cultivated areas. Within the current management system, isolated trees may also contribute significantly to the provision of ecological services by enhancing bird diversity in open areas outside the forest. We identified practices and values linked to isolated tree uses and management through ethnographic data collection. Bird presence and abundance were sampled by 338 point counts in isolated trees and open areas of the agricultural mosaic. Isolated trees were occupied by 18 out of 32 (56%) bird species in the agricultural mosaic, including 8 (25%) endemic forest species. Endemic forest birds were significantly more numerous in isolated trees than in open habitats, both in species richness and abundance (mean P value < 0.001). Overall bird species richness was significantly higher in open areas containing isolated trees, than in areas without isolated trees. Bird species richness in Ficus spp. was significantly higher than in other isolated tree species, although no differences were detected in abundance or within guilds. Community-based management of isolated trees may thus represent an opportunity for convergence between bird conservation goals outside protected areas and local management values and practices.     

Markedly Divergent Tree Assemblage Responses to Tropical Forest Loss and Fragmentation across a Strong Seasonality Gradient

We examine the effects of forest fragmentation on the structure and composition of tree assemblages within three seasonal and aseasonal forest types of southern Brazil, including evergreen, Araucaria, and deciduous forests. We sampled three southernmost Atlantic Forest landscapes, including the largest continuous forest protected areas within each forest type. Tree assemblages in each forest type were sampled within 10 plots of 0.1 ha in both continuous forests and 10 adjacent forest fragments. All trees within each plot were assigned to trait categories describing their regeneration strategy, vertical stratification, seed-dispersal mode, seed size, and wood density. We detected differences among both forest types and landscape contexts in terms of overall tree species richness, and the density and species richness of different functional groups in terms of regeneration strategy, seed dispersal mode and woody density. Overall, evergreen forest fragments exhibited the largest deviations from continuous forest plots in assemblage structure. Evergreen, Araucaria and deciduous forests diverge in the functional composition of tree floras, particularly in relation to regeneration strategy and stress tolerance. By supporting a more diversified light-demanding and stress-tolerant flora with reduced richness and abundance of shade-tolerant, old-growth species, both deciduous and Araucaria forest tree assemblages are more intrinsically resilient to contemporary human-disturbances, including fragmentation-induced edge effects, in terms of species erosion and functional shifts. We suggest that these intrinsic differences in the direction and magnitude of responses to changes in landscape structure between forest types should guide a wide range of conservation strategies in restoring fragmented tropical forest landscapes worldwide.     

Can agroforest woodlots work as stepping stones for birds in the Atlantic forest region?

In fragmented landscapes, agroforest woodlots can potentially act as stepping stones facilitating movement between forest fragments. We assessed the influence of agroforest woodlots on bird distribution and diversity in the Atlantic forest region (SE Brazil), and also tested which categories of species can use different types of connection elements, and whether this use is influenced by the distance to large forest patches. We studied two fragmented landscapes, with and without stepping stones linking large fragments, and one forested landscape. Using a point count, a bird survey was undertaken in the fragmented landscapes in five different elements: large remnants (>400 ha), agroforest woodlots (0.4–1.1 ha), small patches (0.5–7 ha), riparian corridor, and pasture areas (the main matrix). Generalist and open-area species were commonly observed in the agroforest system or other connection elements, whereas only a few forest species were present in these connections. For the latter species, the distance of woodlots to large patches was essential to determine their richness and abundance. Based on our results and data from literature, we suggest that there is an optimal relationship between the permeability of the matrix and the efficiency of stepping stones, which occurs at intermediate degrees of matrix resistance, and is species-dependent. Because the presence of agroforest system favors a higher richness of generalist species, they appeared to be more advantageous for conservation than the monoculture system; for this reason, they should be considered as a management alternative, particularly when the matrix permeability requirement is met.     

Distribution of birds in natural landscape mosaics of old-growth forests in northern Sweden: relations to habitat area and landscape context

We censused breeding birds for three years in natural landscape mosaics of virgin old-growth spruce forest and mire in a large protected forest area in northern Sweden Twenty forest patches, ranging from 0 2 to 17 8 ha in size, were selected in two matrix types, dominated by forest and mire, respectively Patches were very similar with regards to habitat features There was a strong effect of patch area on species richness, but no effect of matrix type Standardization of species richness by rarefaction revealed that small patches (<5 ha) had fewer and large patches (>10 ha) more species than expected Overall distribution of species across patches showed a highly significant nested pattern, indicating that a few habitat generalists occupy all size classes, whereas more demanding species avoid small patches regardless of landscape composition Individual species tended to be distributed evenly across patch classes and no significant edge effect in terms of density of birds was found Our results have bearings on actions to preserve avian diversity in northern boreal forests small patches (<5 ha) provide habitat only for habitat generalists, and therefore larger (>10 ha) patches should be preserved     

Isolation determines patterns of species presence in highly fragmented landscapes

In fragmented landscapes, changes in habitat availability, patch size, shape and isolation may affect survival of local populations. Proposing efficient conservation strategies for such species relies initially on distinguishing the particular effects of those factors. To address these issues, we investigated the occurrence of 3 bird species in fragmented Brazilian Atlantic Forest landscapes. Playback techniques were used to collect presence/absence data of these species inside 80 forest patches, and incidence models were used to infer their occupancy pattern from landscape spatial structure. The relative importance of patch size, shape and surrounding forest cover and isolation was assessed using a model selection approach based on maximum likelihood estimation. The presence of all species was in general positively affected by the amount of surrounding habitat and negatively affected by inter‐patch distances. The joint effects of patch size and the surrounding landscape characteristics were important determinants of occupancy for two species. The third species was affected only by forest cover and mean patch isolation. Our results suggest that local species presence is in general more influenced by the isolation from surrounding forests than by patch size alone. We found evidence that, in highly fragmented landscapes, birds that can not find patches large enough to settle may be able to overcome short distances through the matrix and include several nearby patches within their home‐ranges to complement their resource needs. In these cases, patches must be defined as functionally connected habitat networks rather than mere continuous forest segments. Bird conservation strategies in the Atlantic forest should focus on increasing patch density and connectivity, in order to implement forest networks that reduce the functional isolation between large remnants with remaining core habitat.     

The role of landscape in shaping bird community and implications for landscape management at Nanjing Lukou International Airport

Understanding the patterns of bird diversity and its driving force is necessary for bird strike prevention. In this study, we investigated the effects of landscape on phylogenetic and functional diversity of bird communities at Nanjing Lukou International Airport (NLIA). Bird identifications and counting of individuals were carried out from November 2017 to October 2019. Based on the land-cover data, the landscape was divided into four main types, including farmlands, woodlands, wetlands, and urban areas. Bird phylogenetic and functional diversity were strongly affected by landscape matrix types. Species richness and Faith's phylogenetic distance were highest in woodlands, while mean pairwise distance (MPD), mean nearest-taxon distance (MNTD), and functional dispersion (FDis) were highest in wetlands. Based on the feeding behavior, carnivorous birds had the lowest species richness but had the highest FDis, which implied that carnivorous birds occupied most niches at the NLIA. Moreover, bird assemblages exhibited phylogenetic and functional clustering in the four kinds of landscapes. A variety of landscape attributes had significant effects on species diversity, phylogenetic and functional diversity. Landscape-scale factors played an important role in the shaping of bird communities around NLIA. Our results suggest that landscape management surrounding airports can provide new approaches for policymakers to mitigate wildlife strikes.     

High Bird Species Diversity in Structurally Heterogeneous Farmland in Western Kenya

Tropical ecosystems are globally important for bird diversity. In many tropical regions, land‐use intensification has caused conversion of natural forests into human‐modified habitats, such as secondary forests and heterogeneous agricultural landscapes. Despite previous research, the distribution of bird communities in these forest‐farmland mosaics is not well understood. To achieve a comprehensive understanding of bird diversity and community turnover in a human‐modified Kenyan landscape, we recorded bird communities at 20 sites covering the complete habitat gradient from forest (near natural forest, secondary forest) to farmland (subsistence farmland, sugarcane plantation) using point counts and distance sampling. Bird density and species richness were on average higher in farmland than in forest habitats. Within forest and farmland, bird density and species richness increased with vegetation structural diversity, i.e., were higher in near natural than in secondary forest and in subsistence farmland than in sugarcane plantations. Bird communities in forest and farmland habitats were very distinct and very few forest specialists occurred in farmland habitats. Moreover, insectivorous bird species declined in farmland habitats whereas carnivores and herbivores increased. Our study confirms that tropical farmlands can hardly accommodate forest specialist species. Contrary to most previous studies, our findings show that structurally rich tropical farmlands hold a surprisingly rich and distinct bird community that is threatened by conversion of subsistence farmland into sugarcane plantations. We conclude that conservation strategies in the tropics must go beyond rain forest protection and should integrate structurally heterogeneous agroecosystems into conservation plans that aim at maintaining the diverse bird communities of tropical forest‐farmland mosaics.     

Biogeographical comparison of winter bird assemblages in urban environments in Finland

We studied biogeographical variation of urban bird assemblages in Finland. Winter birds were censused by single-visit study plot method from thirty-one centres of villages or towns along 950 km latitudinal extent. A total twenty-eight bird species was observed and the average density was 61.2 ind./10 ha. The number of dominant species in study areas varied between two and seven and their proportion of the whole assemblage was over 70%. Species richness, but not the density of birds, decreased northwards in pooled data. Higher species richness in south than in north was mainly due to the higher amount of delayed migratory birds (e.g. waterbirds, finches) and southerly distributed bird species. However, in heavily urbanized areas species richness did not decrease northwards. This observation disagreed with the hypothesis that species richness decreased northwards. Bird density, but not species richness, increased with urbanization. In particular, feral pigeon, hooded crow and house sparrow had highest densities in most urbanized areas. As only few bird species are adapted to live in urban areas, species composition and dominant bird species were almost the same in the south and in the north. These urban birds may effectively use energy rich food in feeding tables and overcome the problems of severe climate in the north. This may be the reason why bird species richness does not decrease northwards in urban areas.