Use of Tropical Dry Forests and Agricultural Areas by Neotropical Bird Communities

Agricultural activities represent a global threat to biodiversity, yet little is known about the relative importance of different agricultural land uses in relation to their wildlife communities. We explored bird community structure, diversity, and composition in a landscape dominated by primary tropical dry forest, and in three agricultural systems (i.e., tree orchards, herbaceous cropfields, cattle pastures) to evaluate the way in which birds use different habitats within the landscape. Tropical dry forests had the highest species richness and community evenness, although the bird community in tree orchards was also relatively species rich and even. Cattle pastures had more bird species than cropfields but both habitats were comparatively species poor with low evenness. Our results are related to habitat structure and the spatial location of sites within the landscape matrix. Based on our observations, we recommend including native tree species within agricultural systems and surrounding areas to provide additional resources for birds. Finally, we suggest promoting natural recruitment of native trees and shrubs within cattle pastures to provide suitable habitat for species that use tropical dry forest plants. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

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.     

Functional homogenization of bird communities along habitat gradients: accounting for niche multidimensionality

Aim To test whether functional homogenization of bird communities is promoted by anthropogenic landscape transformation, using specialization and habitat preference indices that account for the multidimensionality of niches. Location Catalonia, north‐east Iberian Peninsula. Methods We used data on bird species occurrences and landscape features in 2834 1‐km² squares. Three orthogonal landscape gradients, which were taken as niche dimensions, were defined by means of principal components analysis (PCA). Specialization and habitat preference indices were created for 103 terrestrial bird species on the basis of their frequency of occurrence variation along the landscape gradients. These indices, together with species rarity, were then averaged for bird communities. We then analysed the patterns of variation of communities’ mean specialization, mean rarity and mean habitat preference values along a gradient of agricultural–forest habitat mosaics. Results Wherever we found a significant variation in the degree of specialization along the agricultural–forest gradient, agricultural habitats held more specialized bird communities than did forest ones and bore, on average, rarer species. Thus, results contradicted our initial hypothesis that humanized areas would bear more functionally homogenized bird communities. Higher α‐diversity values tended to be associated with generalist communities and with those having rarer species. Main conclusions Estimations of bird community specialization for different niche dimensions can behave differently along certain landscape gradients, and some of these differences can be explained by the variation of mean habitat preferences. Thus, we argue that a multidimensional approach to assess average niche breadth of communities can be more informative than a unidimensional measure. Our results suggest that widespread land abandonment and current secondary forest expansion throughout the Mediterranean area are promoting functional homogenization of bird communities. It would be desirable to construct larger‐scale indicators of functional homogenization in order to monitor communities’ responses to widespread landscape changes.     

On humans and wildlife in Mediterranean islands

Aim To investigate the effects of human‐induced landscape changes in Mediterranean islands on the ecological and evolutionary responses of bird communities and populations. The combination of mass extinction of large mammals and massive deforestation by humans was hypothesized to produce new selection regimes to which organisms were likely to respond. Habitat selection and niche breadth have been investigated at the scale of species, and phenotypic variation at the scale of local populations. Location The study was carried out along habitat gradients and in habitat mosaics at different spatial scales on the island of Corsica and in areas of similar size and structure in continental France. Methods Two sets of gradients have been used for investigating habitat selection and niche breadth: gradients of altitude, and gradients of vegetation structure. Population studies focused on the blue tit, Cyanistes caeruleus. Large samples of breeding attempts by this species in 10 habitats provided detailed data on phenotypic variation of fitness‐related traits both on Corsica and on the mainland. Results The extent of niche space used by birds differed substantially depending on which habitat gradient was considered. Many species have been found to contract their habitat niche along the elevation gradient on Corsica compared with the mainland, whereas all species in the vegetation gradient broadened their niche on the island. Breeding patterns of the blue tit differed considerably depending on whether they settle in deciduous oaks (Quercus humilis) or in evergreen sclerophyllous oaks (Quercus ilex). Phenotypic variation of breeding traits was much higher on the island, where more populations were correctly timed for the best breeding period than on the mainland, a pattern that is likely to result from lower dispersal of organisms on the island. Main conclusions The differences in observed niche breadth between the two series of habitat gradients is explained both by the species‐specific ecology of the species and the human‐induced environmental history of Corsica. Large‐scale landscape changes provided new opportunities for island colonization by non‐forest species, which are isolated as small, ‘fugitive’ local populations. In both gradients, forest species that are typical components of the Corsican bird fauna definitely expanded their niche and occupied a wider range of habitats on Corsica than on the mainland. At the population scale, landscapes included habitat patches with contrasted selection regimes, which resulted in high phenotypic variation for many fitness‐related traits. Reduced dispersal of birds on the island resulted in a much higher degree of local differentiation on Corsica than on the mainland.     

Spatial similarity of urban bird communities: a multiscale approach

Aim Human land use, especially urbanization, might homogenize the world's biota. The objective of this study is to find out if urbanization homogenizes wintering bird communities, and if habitat type affects the spatial variation of urban bird communities across spatial scales. Location We compared the quantitative similarity of winter bird communities between town centres, apartment block areas and single‐family house areas across regional and local scales in five towns in northern Finland. Methods The wintering birds were surveyed using a single‐visit study plot (30 ha) method in January and February 2001. The validity of single‐visit and single‐year data was confirmed by using data from several‐visit surveys and multi‐year data set. The level of urbanization was measured according to the number of inhabitants and general structure of the habitat. Results Temporal variability in species richness and total number of individuals was low, both between winters and within winter. Bird community similarity between different habitat types within a single town was about the same as that in similar habitats in different towns. At the regional scale, bird community similarity between town centres (30%) was lower than between areas of apartment blocks (54%) or between areas of single‐family houses (54%). We detected a threshold point between towns of 35,000 and 105,000 inhabitants and between town sizes of 5.0–8.5 km in diameter where human impact causes marked changes in bird community structure. At the local scale, bird community similarity level between apartment block areas (49%) and single‐family house areas (62%) were about the same. Passer domesticus, Parus major and Pica pica dominated the bird communities in residential areas. Different habitat factors affected bird species abundances on the local and regional scales. Conclusions Urbanization cannot be seen as a process that monotonically increases the similarity of bird communities. Our results indicate that the similarity between urban bird communities is dependent on the size of the town, location of the study site within the town and especially the local habitat structure. Because different habitat factors affected bird species abundances, it is difficult to extrapolate bird–habitat relationships derived from one scale to other scales. In wintertime, single‐family house areas are important biodiversity hotspots in cities. Therefore, it is especially important to understand the factors affecting the occurrence of birds in the single‐family house area in order to maintain or even increase diversity on winter birds in other urban habitats.     

Composition and diversity of bird communities in Swedish farmland–forest mosaic landscapes

CapsuleThe amount of forest (at local and landscape scales) and occurrence of residual habitats at the local scale are shown to be the major factors influencing bird community composition in farmland–forest landscapes in central Sweden.

Aims To investigate the importance of local habitat and landscape structure for breeding birds in farmland–forest landscapes in central Sweden.

Methods Breeding birds were censused at 292 points. A detailed habitat mapping was made within 300 m of the points. Within a 300–600 m radius only two major habitats (forests and arable fields) were identified.

Results Cluster analyses of bird communities identified three site types that also differed in habitat composition: (i) partially forested sites in forested landscapes; (ii) heterogeneous sites with residual habitats in mosaic landscapes; and (iii) field-dominated farmland sites in open landscapes. A total of 19 of 25 farmland bird species (restricted to farmland or using both farmland and forest) had the highest abundance in farmland sites with mosaics of forest and farmland, while only six farmland species had the highest abundance in field-dominated sites. The bird community changed from being dominated by farmland species to being dominated by forest species (common in forest landscapes without farmland) at small proportions (10–20%) of forest at the local scale. A major difference in habitat composition between heterogeneous and field-dominated sites was the occurrence of different residual habitats (e.g. shrubby areas and seminatural grasslands). These habitats seemed to influence bird community composition more than land-use, despite covering <10% of the area. Seminatural grasslands were important for bird community composition and species-richness, but grazing seemed to be less important. Among different land-use types, cereal crops were the least preferred fields. Set-asides with tall vegetation and short rotation coppices were positively associated with species-richness of farmland birds.

Conclusion In general, the composition of the landscape was important for bird community composition, although amount and distribution of forests, occurrence of residual habitats and land-use of fields at the local scale had the strongest influence on bird community composition. The possible implications of these patterns for managing farmland–forest landscapes are discussed.     

Influence of habitat complexity and landscape configuration on pollination and seed-dispersal interactions of wild cherry trees

Land-use intensification is a major cause for the decline in species diversity in human-modified landscapes. The loss of functionally important species can reduce a variety of ecosystem functions, such as pollination and seed dispersal, but the intricate relationships between land-use intensity, biodiversity and ecosystem functioning are still contentious. Along a gradient from forest to intensively used farmland, we quantified bee species richness, visitation rates of bees and pollination success of wild cherry trees (Prunus avium). We analysed the effects of structural habitat diversity at a local scale and of the proportion of suitable habitat around each tree at a landscape scale. We compared these findings with those from previous studies of seed-dispersing birds and mammals in the same model system and along the same land-use gradient. Bee species richness and visitation rates were found to be highest in structurally simple habitats, whereas bird species richness—but not their visitation rates—were highest in structurally complex habitats. Mammal visitation rates were only influenced at the landscape scale. These results show that different functional groups of animals respond idiosyncratically to gradients in habitat and landscape structure. Despite strong effects on bees and birds, pollination success and bird seed removal did not differ along the land-use gradient at both spatial scales. These results suggest that mobile organisms, such as bees and birds, move over long distances in intensively used landscapes and thereby buffer pollination and seed-dispersal interactions. We conclude that measures of species richness and interaction frequencies are not sufficient on their own to understand the ultimate consequences of land-use intensification on ecosystem functioning.     

Recovery of the Bird Community after a Mine Spill and Landscape Restoration of a Mediterranean River

In Mediterranean areas, river systems are key for maintaining regional biodiversity by providing a high diversity of habitats. We studied bird community recovery for 9 years (2001–2009) during landscape restoration and Guadiamar Green Corridor establishment in the area affected by the Aznalcóllar mine spill (SW Spain, 1998). One year following plant restoration (3 years after the spill), values for α‐ and β‐bird species diversity were high, sooner than reported for similar restoration processes elsewhere. Species richness, ecological diversity, and abundance increased only slightly in the following 8 years. Overlap between communities in sequential years, measured by similarity indexes, increased throughout the study period to about 70% during final survey years, and most breeding bird species present before the accident again inhabit the area. Only 5 years after the mine accident, bird communities in the restored site were similar in species richness, abundance, and diversity to an unaffected reference site; redundancy analysis demonstrated that bird communities were also similar between the reference river and the Guadiamar. Despite the severity of the mine accident, our results suggest a swift recovery of the bird community. We attribute this success to the rapid restoration of habitat availability and the resilience of the birds. This long‐term study contributes to our limited knowledge of bird species response to habitat restoration following toxic spills in Mediterranean habitats.     

Forest edges have high conservation value for bird communities in mosaic landscapes

A major conservation challenge in mosaic landscapes is to understand how trait‐specific responses to habitat edges affect bird communities, including potential cascading effects on bird functions providing ecosystem services to forests, such as pest control. Here, we examined how bird species richness, abundance and community composition varied from interior forest habitats and their edges into adjacent open habitats, within a multi‐regional sampling scheme. We further analyzed variations in Conservation Value Index (CVI), Community Specialization Index (CSI) and functional traits across the forest‐edge‐open habitat gradient. Bird species richness, total abundance and CVI were significantly higher at forest edges while CSI peaked at interior open habitats, i.e., furthest from forest edge. In addition, there were important variations in trait‐ and species‐specific responses to forest edges among bird communities. Positive responses to forest edges were found for several forest bird species with unfavorable conservation status. These species were in general insectivores, understorey gleaners, cavity nesters and long‐distance migrants, all traits that displayed higher abundance at forest edges than in forest interiors or adjacent open habitats. Furthermore, consistently with predictions, negative edge effects were recorded in some forest specialist birds and in most open‐habitat birds, showing increasing densities from edges to interior habitats. We thus suggest that increasing landscape‐scale habitat complexity would be beneficial to declining species living in mosaic landscapes combining small woodlands and open habitats. Edge effects between forests and adjacent open habitats may also favor bird functional guilds providing valuable ecosystem services to forests in longstanding fragmented landscapes.     

Contrasting trait assembly patterns in plant and bird communities along environmental and human‐induced land‐use gradients

Human‐driven environmental changes can induce marked shifts in the functional structure of biological communities with possible repercussion on important ecosystem functions and services. At the same time it remains unclear to which extent these changes may differently affect various types of organisms. We investigated species richness and community functional structure of species assemblages at the landscape scale (1 km² plots) for two contrasting model taxa, i.e. plants (producers and sessile organisms) and birds (consumers and mobile organisms), along topography, climate, landscape heterogeneity, and land‐use (agriculture and urbanization) gradients in a densely populated region of Switzerland. Our study revealed that agricultural and urban land uses drove marked shifts in the functional structure of biological communities compared to changes along climate and topography gradients, especially for plants, while for birds these changes were comparable. Agricultural and urban land uses enhanced divergence in traits related to resource use for birds (diet and nesting), growth forms, dispersal, and reproductive traits for plants, while it induced convergence in vegetative plant traits (plant height and leaf dry matter content). These results suggest that contrasting assembly patterns may arise within and across taxonomic groups along the same environmental gradients as result of distinct underlying processes and ‘organism‐specific’ environmental perceptions. Our results further suggest a potential homogenization of biological communities, as well as low functional diversity and redundancy levels of bird assemblages in our human‐dominated study region. This might potentially compromise the maintenance of key ecological processes under future environmental changes.     

Effects of Habitat Structure and Adjacent Habitats on Birds in Tropical Rainforest Fragments and Shaded Plantations in the Western Ghats, India

As large nature reserves occupy only a fraction of the earth’s land surface, conservation biologists are critically examining the role of private lands, habitat fragments, and plantations for conservation. This study in a biodiversity hotspot and endemic bird area, the Western Ghats mountains of India, examined the effects of habitat structure, floristics, and adjacent habitats on bird communities in shade-coffee and cardamom plantations and tropical rainforest fragments. Habitat and birds were sampled in 13 sites: six fragments (three relatively isolated and three with canopy connectivity with adjoining shade-coffee plantations and forests), six plantations differing in canopy tree species composition (five coffee and one cardamom), and one undisturbed primary rainforest control site in the Anamalai hills. Around 3300 detections of 6000 individual birds belonging to 106 species were obtained. The coffee plantations were poorer than rainforest in rainforest bird species, particularly endemic species, but the rustic cardamom plantation with diverse, native rainforest shade trees, had bird species richness and abundance comparable to primary rainforest. Plantations and fragments that adjoined habitats providing greater tree canopy connectivity supported more rainforest and fewer open-forest bird species and individuals than sites that lacked such connectivity. These effects were mediated by strong positive effects of vegetation structure, particularly woody plant variables, cane, and bamboo, on bird community structure. Bird community composition was however positively correlated only to floristic (tree species) composition of sites. The maintenance or restoration of habitat structure and (shade) tree species composition in shade-coffee and cardamom plantations and rainforest fragments can aid in rainforest bird conservation in the regional landscape.     

Time and travelling costs during chick‐rearing in relation to habitat quality in Little Owls Athene noctua

In many bird species, parents adjust their home‐ranges during chick‐rearing to the availability and distribution of food resources, balancing the benefits of energy intake against the costs of travelling. Over recent decades, European agricultural landscapes have changed radically, resulting in the degradation of habitats and reductions in food resources for farmland birds. Lower foraging success and longer foraging trip distances that result from these changes are often assumed to reduce the reproductive performance of parents, although the mechanisms are not well understood. We tested the behavioural response of chick‐rearing Little Owls Athene noctua to variation in habitat diversity in an agricultural landscape. We equipped females with GPS loggers and received adequate range‐use data for 19 individuals (6063–14 439 locations per bird). In habitats dominated by homogeneous cropland habitats, home‐ranges were over 12 ha in size, whereas in highly diverse habitats they were below 2 ha. Large home‐ranges were associated with increased flight activity (117% of that of birds in small home‐ranges) and distances travelled per night (152%), increased duration of foraging trips (169%) covering larger distances (246%), and reduced nest visiting rates (81%). The study therefore provides strong correlative evidence that Little Owls breeding in monotonous farmland habitats expend more time and energy for a lower benefit in terms of feeding rates than do birds in more heterogeneous landscapes. As nestling food supply is the main determinant of chick survival, these results suggest a strong impact of farmland characteristics on local demographic rates. We suggest that preserving and creating islands of high habitat diversity within uniform open agricultural landscapes should be a key target in the conservation of Little Owl populations.     

The spatial distribution of birds and carabid beetles in pine plantation forests: the role of landscape composition and structure

Aim To evaluate the joint and independent effects of spatial location, landscape composition and landscape structure on the distribution patterns of bird and carabid beetle assemblages in a mosaic landscape dominated by pine plantation forests. Location A continuous 3000‐ha landscape mosaic with native maritime pine Pinus pinaster plantations of different ages, deciduous woodlands and open habitats, located in the Landes de Gascogne forest of south‐western France. Methods We sampled breeding birds by 20‐min point counts and carabid beetles by pitfall trapping using a systematic grid sampling of 200 points every 400 m over the whole landscape. Explanatory variables were composed of three data sets derived from GIS habitat mapping: (1) spatial variables (polynomial terms of geographical coordinates of samples), (2) landscape composition as the percentage cover of the six main habitats, and (3) landscape structure metrics including indices of fragmentation and spatial heterogeneity. We used canonical correspondence analysis with variance partitioning to evaluate the joint and independent effects of the three sets of variables on the ordination of species assemblages. Moran's I correlograms and Mantel tests were used to assess for spatial structure in species distribution and relationships with separate landscape attributes. Results Landscape composition was the main factor explaining the distribution patterns of birds and carabids at the mesoscale of 400 × 400 m. Independent effects of spatial variables and landscape structure were still significant for bird assemblages once landscape composition was controlled for, but not for carabid assemblages. Spatial distributions of birds and carabids were primarily influenced by the amount of heathlands, young pine plantations, herbaceous firebreaks and deciduous woodlands. Deciduous woodland species had positive responses to edge density, while open habitat species were positively associated with mean patch area. Main conclusions Forest birds were favoured by an increase in deciduous woodland cover and landscape heterogeneity, but there was no evidence for a similar effect on carabid beetles. Fragmentation of open habitats negatively affected both early‐successional birds and carabids, specialist species being restricted to large heathlands and young plantations. Several birds of conservation concern were associated with mosaics of woodlands and grasslands, especially meadows and firebreaks. Conserving biodiversity in mosaic plantation landscapes could be achieved by the maintenance of a significant amount of early‐successional habitats and deciduous woodland patches within a conifer plantation matrix.     

Species’ thermal preferences affect forest bird communities along landscape and local scale habitat gradients

The spatial distributions of species, and the resulting composition of local communities, are shaped by a complex interplay between species’ climatic and habitat preferences. We investigated this interaction by analyzing how the climatic niches of bird species within given communities (measured as a community thermal index, CTI) are related to vegetation structure. Using 3129 bird communities from the French Breeding Bird Survey and an information theoretic multimodel inference framework, we assessed patterns of CTI variation along landscape scale gradients of forest cover and configuration. We then tested whether the CTI varies along local scale gradients of forest structure and composition using a detailed data set of 659 communities from six forests located in northwestern France. At landscape scale, CTI values decreased with increasing forest cover, indicating that bird communities were increasingly dominated by cold‐dwelling species. This tendency was strongest at low latitudes and in landscapes dominated by unfragmented forest. At local scale, CTI values were higher in mature deciduous stands than in conifer or early stage deciduous stands, and they decreased consistently with distance from the edge of forest. These trends underpin the assertion that species’ habitat use along forest gradients is linked with their climatic niche, although it remains unclear to what extent it is a direct consequence of microclimatic variation among habitats, or a reflection of macroscale correlations between species’ thermal preferences and their habitat choice. Moreover, our results highlight the need to address issues of scale in determining how habitat and climate interact to drive the spatial distribution of species. This will be a crucial step towards accurate predictions of changes in the composition and dynamics of bird communities under global warming.     

Heterogeneous Landscapes on Steep Slopes at Low Altitudes as Hotspots of Bird Diversity in a Hilly Region of Nepal in the Central Himalayas

Understanding factors determining the distribution of species is a key requirement for protecting diversity in a specific area. The aim of this study was to explore the factors affecting diversity and distribution of species of birds on different forested hills in central Nepal. The area is rich in species of birds. Because the area is characterized by steep gradients, we were also interested in the importance of altitude in determining the diversity and species composition of the bird communities. We assessed bird diversity and species composition based on point observations along a gradient of increasing altitude in two valleys (Kathmandu and Palung) in central Nepal. Data on environmental variables were also collected in order to identify the main determinants of bird diversity and species composition of the bird communities. We recorded 6522 individual birds belonging to 146 species, 77 genera and 23 families. Resident birds made up 80% (117 species) of the total dataset. The study supported the original expectation that altitude is a major determinant of species richness and composition of bird communities in the area. More diverse bird communities were found also in areas with steeper slopes. This together with the positive effect of greater heterogeneity suggests that forests on steep slopes intermixed with patches of open habitats on shallow soil at large spatial scales are more important for diverse bird communities than more disturbed habitats on shallow slopes. In addition, we demonstrated that while different habitat characteristics such as presence of forests edges and shrubs play an important role in driving species composition, but they do not affect species richness. This indicates that while habitat conditions are important determinants of the distribution of specific species, the number of niches is determined by large scale characteristics, such as landscape level habitat heterogeneity and altitude. Thus, to protect bird diversity in the mid-hills of central Nepal, we should maintain diverse local habitats (viz. forest, shrubs, open land, etc.) but also make sure the natural habitats on steeper slopes with large scale heterogeneity are maintained.     

Landscape‐scale habitat availability,and not local geography,predicts migratory landbird stopover across the Gulf of Maine

While it is clear that many migratory behaviors are shared across taxa, generalizable models that predict the distribution and abundance of migrating taxa at the landscape scale are rare. In migratory landbirds, ephemeral concentrations of refueling birds indicate that individual behaviors sometimes produce large epiphenomena in particular geographic locations. Identifying landscape factors that predict the distribution and abundance of birds during migratory stopover will both improve our understanding of the migratory process and assist in broad, regionally relevant conservation. In this study we used autumnal passerine stopover data from a five‐year period and eleven stopover sites across coastal Maine, USA, to test four broad hypotheses of migrant distribution and abundance that have been supported in other regions: a) the community characteristics of the pool of potential migrants, b) a site's local geography, c) landscape composition and configuration measured at different spatial scales, and d) interactions between these factors. Our final model revealed that birds concentrate at ‘habitat islands’, sites that possess a disproportionate percentage of the vegetated habitat in the 4‐km surrounding landscape. The strength of this pattern, however, was inversely proportional to a species' remaining migratory distance. Our results corroborate several studies that emphasize the importance of land cover composition at finer spatial scales (< 80 km²) for predicting the stopover distribution and abundances of migratory birds. This suggests that different migrants likely assess stopover sites with similar mechanisms along their migratory route, and these commonalities may be broadly applied to identify stopover locations of conservation importance across the continent.     

黄淮平原农业景观鸟类多样性及生境差异

农业景观中的鸟类多样性对生态系统功能和服务的形成与维持具有重要作用。黄淮平原区是我国最重要的农业景观区之一,为探讨区域内农业景观中鸟类多样性特征和不同生境间的差异,在研究区农业景观不同生境中布设样点,调查繁殖期鸟类多样性特征。结果显示:(1)共记录到32科、49属、66种的10044只个体,但优势科属明显;(2)物种丰富度、多样性和均匀度均表现出在沟渠、湖泊生境中较高,农田和村庄生境中相对较低,但物种多度呈现出村庄生境中最高,其次是沟渠和农田生境,湖泊生境中最低;(3)在区系分布上,各生境中均以广布种为主,生态类群上,鸣禽在各生境中均占绝对优势,涉禽和游禽主要分布在沟渠和湖泊生境中,从居留型来看,留鸟是各生境中的主导类群,候鸟、旅鸟和迷鸟比例很低;(4)鸟类群落异质性分析显示,各生境间的相似性总体上较高,表明区域内农业景观中鸟类组成具有较高的重叠性。研究显示农业景观中湖泊和沟渠的存在能有效的提高区域鸟类的丰富度和多样性,而沟渠的存在能有效的提高鸟类个体多度,农田和村庄有助于特定类群多度的增加,因此在未来的区域持续农业景观的构建中一方面要重视自然、半自然非农生境的作用,另一方面也不能忽视不同生物类群对景观异质性响应和对生境特征需求的差异。     

Indices of bird-habitat preference from field surveys of birds and remote sensing of land cover: a study of south-eastern England with wider implications for conservation and biodiversity assessment

Aim This paper describes the development of novel indices of bird‐habitat preference to examine bird species’ use of habitats and their distributions relative to habitats. It assesses the implications for bird conservation regionally and the scope for biodiversity assessments generally. Location A 200 km by 400 km area of farmland with seminatural and urban areas, covering south‐eastern England. Methods Cluster analysis was used to link birds to landscapes. Cluster centroid coordinate values were processed to derive indices of bird‐habitat preference. Further developments assessed the relative values of individual habitats for birds. Results Clustering objectively linked birds to landscapes. Maps of the clusters showed strong regional patterns associated with distinctive habitat assemblages. Derived indices related bird species directly to individual habitats and habitats to birds. Even rare species and scarce habitats showed successful linkages, often to each other. Objective corroboration strongly supported the associations of coastal, wetland, urban and woodland birds and habitats; but, it suggested that farmland birds, whose numbers have nearly halved since 1977, may prefer alternative habitats. Main conclusions Land cover maps from remote sensing provide an effective way to link birds to habitats and vice versa. Thus, generalized habitat maps might be used to extrapolate localized or sample‐based bird observations or the results of autecological studies, helping to predict and understand bird distributions in the wider countryside. The weak links between farmland birds and farmland habitats in a region dominated by farming, suggests that reasons for the decline in farmland birds may be deep seated and thus hard to reverse. The procedures described are repeatable elsewhere and applicable more generally to evaluate landscapes and biodiversity. It is suggested that remote sensing could rarely be bettered as a means of assessing habitats, comprehensively, over wide areas, in most parts of the world.     

Land rehabilitation and the conservation of birds in a degraded Afromontane landscape in northern Ethiopia

The few remaining Afromontane forest fragments in northern Ethiopia and the surrounding degraded, semiarid matrix form a habitat mosaic of varying suitability for forest birds. To evaluate the effect of recent land rehabilitation efforts on bird community composition and diversity, we studied bird species distributions in ten small forest fragments (0.40–20.95 ha), five grazing exclosures (10-year-old forest restoration areas without wood extraction and grazing livestock) and three grazed matrix sites during the rainy season (July–October 2004) using 277 one-hour species counts. Based on the distribution pattern of 146 bird species, sites were assigned to one of three bird communities (birds of moist forest, dry forest or degraded savanna), each occupying a well-defined position along an environmental gradient reflecting decreasing vegetation structure and density. All three communities were representative of the avifauna of Afrotropical Highland open forest and woodland with a high proportion of invasive and competitive generalist species (31%). Apart from these, exclosures shared more species with forest fragments (20%) than did the grazed matrix (5%), indicating local ecosystem recovery. By increasing habitat heterogeneity, exclosures have the potential to enhance landscape connectivity for forest birds and are, therefore, an effective instrument for conserving species in a fragmented landscape. However, 52 bird species (36%) occurred exclusively within forest patches and many forest birds that use exclosures are unlikely to maintain viable populations when forest fragments disappear, particularly as forest fragments may be a critical resource during the hot dry season. This highlights the high conservation value of small isolated forest fragments for less tolerant, forest-limited and/or biome-restricted species.     

Bird community structure in natural and urbanized habitats along an altitudinal gradient in Pauri district (Garhwal Himalaya) of Uttarakhand state, India

In the Indian subcontinent there is hardly any study that compares the bird community structure of urban/suburban areas with those of forest habitat. The present survey identified diverse assemblages of birds in the Pauri district at different elevations. A total of 125 bird species belonging to 40 families including two least count species (Lophura leucomelanos and Pucrasia marcolopha) were recorded during this survey in the forest and urbanized habitats of Pauri District (Garhwal Hiamalaya) of Uttarakhand state, India. The high elevation (Pauri 1600–2100 m a.s.l.), mid elevation (Srikot-Khanda 900–1300 m a.s.l.) and low elevation (Srinagar 500–900 m a.s.l.) contributed 88.8%, 63.2% and 58.4% of the total species respectively. Rarefaction analysis and Shannon diversity index showed that the high elevation forest habitat had highest bird species richness (BSR) and bird species diversity (BSD) followed by the mid and then the low elevation forests. BSR and BSD fluctuated across seasons at all elevations but not across habitat types. Present study provides a base line data about avian community composition in urbanized and natural habitats along altitudinal gradient in the study area. This information may be useful to the conservation biologists for the better management and conservation of the avifauna in the Western Himalaya, a part of one of the hot biodiversity spots of the world.