Variation In Bird Species Richness Research Articles

Landscape heterogeneity affects diurnal raptor communities in a sub-tropical region of northwestern Himalayas, India.

Raptors are highly sensitive to environmental and human-induced changes. In addition, several species of raptors exist in considerably small numbers. It is thus critical to conserve raptors and their habitats across relatively larger landscapes. We examined the diurnal raptor assemblages and seasonality in a subtropical habitat in India’s northwestern Himalayas. Quantitative data on diurnal birds of prey and their habitat features across six distinct habitat types were collected from 33 sample sites. We observed 3,434 individuals of 28 diurnal raptors belonging to two orders and three families during a two-year survey from December 2016 to November 2018. A significant variation in bird species richness and abundance was found across habitats and seasons, with farmlands and winters being the most diverse and speciose. The generalized linear model, used to determine raptor community responses, indicated that elevation and proximity to dumping sites significantly affected the raptor abundance. The non-metric multidimensional scaling (NMDS) revealed significant differences in raptor assemblages across the habitat types. The study concluded that raptors’ persistence is largely determined by their preference for favourable feeding, roosting, and nesting opportunities. The presence of protected and habitat-exclusive species validates the high conservation importance of these ecosystems, particularly the forest patches and farmlands, necessitating robust conservation and management measures in this part of northwestern Himalaya.

Bird monitoring in a tropical savanna conservation reserve suggests Noisy Miners Manorina melanocephala and adaptive fire management should be a future management focus

Long-term monitoring of bird communities over time can provide important data for management, and the adaptation of that management over time. We examined data from bird surveys across 37 sites sampled in five different years from 2009 to 2017 in a 56,000-ha tropical savanna conservation reserve, in northern Queensland. Because of the limitations of the survey method and the lack of environmental data for sites, we examined broad patterns in the abundance of small- and large-bodied birds, abundance of Noisy Miners Manorina melanocephala, land type, survey year, and time since last fire. There was some variation in bird species richness and abundance across the land types, years sampled and Noisy Miner abundance; however, the clearest pattern was decreasing numbers of small-bodied birds and increasing Noisy Miner abundance, and an association between time since fire (i.e. <3 years, >5 years), Noisy Miner abundance and diversity in other birds. The apparent and potentially compounding interaction of Noisy Miners and fire could be an emerging problem. Future fire management needs to be embedded in a program of targeted question-driven monitoring and adaptive management, to provide more assured approaches to prescribed burning that enhances bird conservation.

Metrics of Lidar-Derived 3D Vegetation Structure Reveal Contrasting Effects of Horizontal and Vertical Forest Heterogeneity on Bird Species Richness

The structural heterogeneity of vegetation is a key factor for explaining animal diversity patterns at a local scale. Improvements in airborne light detection and ranging (lidar) technologies have enabled researchers to study forest 3D structure with increasing accuracy. Most structure–animal diversity work has focused on structural metrics derived from lidar returns from canopy and terrain features. Here, we built new lidar structural metrics based on the Leaf Area Density (LAD) at each vegetation height layer, and used these metrics to study how different aspects of forest structural heterogeneity explain variation in bird species richness. Our goals were to test: (1) whether LAD-based metrics better explained bird species richness compared to metrics based on the top of the canopy; and (2) if different aspects of structural heterogeneity had diverse effects on bird richness. We used discrete lidar data together with 61 breeding landbird points provided by the National Ecological Observatory Network at five forest sites of the eastern US. We used the lidar metrics as predictors of bird species richness and analyzed the shape of the response curves against each predictor. Metrics based on LAD measurements had better explanatory power (43% of variance explained) than those based on the variation of canopy heights (32% of variance explained). Dividing the forest plots into smaller grids allowed us to study the within-plot horizontal variation of the vertical heterogeneity, as well as to analyze how the vegetation density is horizontally distributed at each height layer. Bird species richness increased with horizontal heterogeneity, while vertical heterogeneity had negative effects, contrary to previous research. The increasing capabilities of lidar will allow researchers to characterize forest structure with higher detail. Our findings highlight the need for structure–animal diversity studies to incorporate metrics that are able to capture different aspects of forest 3D heterogeneity.

Long-term species richness-abundance dynamics in relation to species departures and arrivals in wintering urban bird assemblages

Abstract Temporal dynamics of local assemblages depend on the species richness and the total abundance of individuals as well as local departure and arrival rates of species. We used urban bird survey data collected from the same 31 study plots and methods during three winters (1991–1992; 1999–2000 and 2009–2010) to analyze the temporal relationship between bird species richness and total number of individuals (abundance). We also evaluated local departures and arrivals of species in each assemblage. In total, 13,812 individuals of 35 species were detected. The temporal variation in bird species richness followed the variation in the total number of individuals. The numbers of local departure and arrival events were similar. Also, the mean number of individuals of the recently arrived species (8.6) was almost the same as the mean number of individuals of the departed species (8.2). Risk of species departure was inversely related to number of individuals. Local species richness increased by one species when the total abundance of individuals increased by around 125 individuals and vice versa. Our results highlight the important role of local population departures and arrivals in determining the local species richness-abundance dynamics in human-dominated landscapes. Local species richness patterns depend on the total number of individuals as well as both the departure-arrival dynamics of individual species as well as the dynamics of all the species together. Our results support the more individuals hypothesis, which suggests that individual-rich assemblages have more species.

Using Macroinvertebrates and Birds to Assess the Environmental Status of Wetlands across Different Climatic Zones in Southwestern Ethiopia

We investigated the variation in macroinvertebrate and bird fauna of 12 different freshwater wetlands located in three different climatic zones of southwestern Ethiopia. Data on macroinvertebrates, birds, physico-chemical water quality variables, human disturbance and vegetation cover were collected from 62 sampling sites during the dry and wet season of 2015. Generalized linear mixed models (GLMMs) were used to identify the most important variables explaining the variation in macroinvertebrates and birds. Twenty four percent of the variation in macroinvertebrate richness was explained by a combination of vegetation cover and dissolved oxygen, whereas 34% of the variation in macroinvertebrate abundance was explained by a combination of dissolved oxygen saturation, electric conductivity, total phosphorus and vegetation cover. A combination of water depth, dissolved oxygen, human disturbance and macroinvertebrate abundance explained about 34% and 31% of variation in bird species richness and abundance, respectively. Richness and abundance of macroinvertebrate and wetland dependent birds were significantly (P < 0.05) different between wetlands. When investigating the ecological status of wetlands, local environmental conditions of wetland should be taken into account for the development of wetland conservation strategies.

Seasonal Variation in Bird Species Richness and Abundance in Riparian Galleries in Southern Portugal

Riparian ecosystems are critical in maintaining biodiversity on a regional scale, which is particularly important for open agroforestry systems. We evaluated bird species richness and abundance in three different distances from the stream (0, 125 and 250 m) in Cork and Holm Oak forest systems (Montado) in southern Portugal. We used 5-minute point-counts to survey birds in two daily periods (morning and afternoon) of three different seasons (breeding season, summer-autumn migration and winter), to describe seasonal and daily variations in the use of riparian galleries and adjacent areas by birds. To assess whether birds move actively from the surrounding matrix into the riparian gallery, we installed mist-nets in mid-summer, autumn migration and winter periods, in two sites adjacent to streams, and recorded flight direction of all passerines trapped in the mist-nets. Both species richness and bird abundance were significantly higher in the riparian gallery than in the adjacent matrix. Species richness was significantly higher during the summer-autumn migration period, and bird abundance significantly lower during the breeding season. Apart from the Short-toed Treecreeper Certhia brachydactyla, Nuthatch Sitta europaea and Chaffinch Fringilla coelebs, all other species (e.g. Blackbird Turdus merula and Sardinian Warbler Sylvia melanocephala) were generally more abundant closer to the stream than at 250 m away. A significantly higher percentage of birds moved from the surrounding matrix into the riparian gallery in mid-summer, but not during the autumn migration and winter, which suggests that microclimatic conditions are important to explain observed seasonal differences. This study shows the importance of considering seasonal variation for the management of passerine bird populations in riparian galleries of Mediterranean areas. A well conserved riparian gallery appears to be a keystone structure exerting a strong influence on the number of bird species associated with surrounding agro-forestry systems such as the Montado.

A global, remote sensing‐based characterization of terrestrial habitat heterogeneity for biodiversity and ecosystem modelling

AbstractAimHabitat heterogeneity has long been recognized as a key landscape characteristic determining biodiversity patterns. However, a lack of standardized, large‐scale, high‐resolution and temporally updatable heterogeneity information based on direct observations has limited our understanding of this connection and its effective use for biodiversity conservation. To address this, we develop here remote sensing‐based metrics to characterize global habitat heterogeneity at 1‐km resolution and assess their value for biodiversity modelling.LocationGlobal.MethodsWe develop 14 heterogeneity metrics (available at http://www.earthenv.org) based on the textural features of the enhanced vegetation index (EVI) imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS), and closely examine a complementary core set of six of these metrics. We evaluate their ability to provide fine‐grain habitat heterogeneity by comparing the heterogeneity information captured by them with that measured by 30‐m Landsat‐based land‐cover data. Using spatial autoregressive models, we then compare their utility with that of more conventional metrics (derived from topography or categorical land‐cover data) for modelling the species richness of bird communities across the conterminous United States based on Breeding Bird Survey data.ResultsThe newly derived metrics capture different aspects of habitat heterogeneity and provide fine‐grain information for locations deemed homogeneous by traditional land‐cover classifications at both continental and global extents. Most of them strongly exceed conventional heterogeneity variables in capturing the spatial variation in bird species richness, with Homogeneity emerging as the strongest predictor.Main conclusionsThis study develops and validates the performance of readily usable metrics of textural measures capturing fine‐grain habitat heterogeneity. The presented metrics outperform conventional measures in capturing detailed spatial variation in habitats and in predicting key biodiversity patterns. They provide a rigorous and comparable basis for understanding heterogeneity–diversity relationships, and offer a powerful tool for monitoring and understanding the responses of biodiversity and ecosystems to the changing environment.

Andean bird responses to human disturbances along an elevational gradient

Understanding patterns of species diversity along environmental gradients is essential to the study of biodiversity. Numerous studies have found variation in species richness and composition of bird communities along elevational gradients, and several others described bird diversity changes following anthropogenic disturbances. Surprisingly, few studies have attempted to disentangle their separate effects on bird assemblages. Here, we explored variation in bird species richness and composition at different levels and types of disturbance along a 4000-m elevational range in the tropical Andes. Bird counts and disturbance measurements were conducted at 85 points distributed along the gradient within Cotapata National Park, Bolivia. Disturbances accounted for in our study correspond to the often overlooked ‘moderate’ levels of disturbance that occur in the Tropical Andes. Diversity patterns were described and compared with GLM models (for species richness) and CCA models (for species composition). We found that bird communities were structured by elevation and disturbance. Species richness decreased with both elevation and habitat openness. Anthropogenic disturbances also modified community composition within the same elevational ranges. We conclude that, whereas elevation remained the most important variable explaining bird species composition, disturbance explained species richness patterns to a higher extent.

Effects of monoculture and polyculture practices in oil palm smallholdings on tropical farmland birds

Industrial oil palm expansion has led to dramatic landscape changes that have negatively affected forest biodiversity in the tropics. In contrast to large-scale plantations, oil palm smallholdings may support greater levels of biodiversity through the implementation of multi-cropping system or polyculture. We examined bird species richness, together with community structure, conservation status, and feeding guild of existing smallholdings in Peninsular Malaysia. Based on point transect sampling, we sampled birds in 100 smallholdings that practiced either monoculture or polyculture farming. Our results revealed that bird species richness was significantly greater in monoculture smallholdings than in polyculture smallholdings, but the opposite was true for bird abundance. Non-forest birds constituted the major species of bird communities in oil palm smallholdings. However, we found that the abundances of insectivores and frugivores were greater in polyculture smallholdings than in monoculture smallholdings. In the monoculture models, predictor variables explained 11.31–19.98% of the variation in bird species richness. When polyculture was being practiced, bird species richness increased significantly with the height of ground vegetation cover, distance to major roads, and distance to rice fields. In the polyculture models, predictor variables accounted for 11.71–24.85% of the variation in bird species richness. We also found that bird species richness increased significantly with height of ground vegetation, but it decreased with ground vegetation cover and distance to rivers. The evidence from this study suggests that monoculture and polyculture farming were able to maintain farmland biodiversity in smallholdings, at least for birds, but differed in richness, population, and feeding guild.

Patterns of bird functional diversity on land‐bridge island fragments

The loss of species diversity due to habitat fragmentation has been extensively studied. In contrast, the impacts of habitat fragmentation on functional diversity remains relatively poorly understood. We conducted bird functional diversity studies on a set of 41 recently isolated land-bridge islands in the Thousand Island Lake, China. We analysed differences in bird species richness and a recently developed suite of complementary functional diversity indices (FRic, volume of functional space occupied; FEve, evenness of abundance distribution in the functional trait space; FDiv, divergence in the distribution of abundance in the trait volume) across different gradients (island area and isolation). We found no correlations between FRic and FEve or FEve and FDiv, but negative correlations between FRic and FDiv. As predicted, island area accounted for most of the variation in bird species richness, whereas isolation explained most of the variation in species evenness (decreasing species evenness with increasing isolation). Functional diversity appears to be more strongly influenced by habitat filtering as opposed to limiting similarity. More specifically, across all islands, both FRic and FEve were significantly lower than expected for randomly assembled communities, but FDiv showed no clear patterns. FRic increased with island area, FEve decreased with island area and FDiv showed no clear patterns. Our finding that FEve decreases with island area at TIL may indicate low functional stability on such islands, and as such large islands and habitat patches may deserve extra attention and/or protection. These results help to demonstrate the importance of considering the effects of fragmentation on functional diversity in habitat management and reserve design plans.

Changes in bird species richness through different levels of urbanization: Implications for biodiversity conservation and garden design in Central Brazil

Urban processes lead to species loss. Palmas is a young city under construction; thus, it provides a rare opportunity to analyze changes in bird richness in a developing city. Eighty city blocks, which were classified into five different categories according to different levels of urbanization, were sampled. Bird counting took place during a dry season and a rainy season in four parallel transects in each block. In these blocks, we estimated 20 variables related to woody vegetation, land cover and type of urban use. The estimated bird species richness for the study area was very high (151 species); nevertheless, species reduction occurred as a function of the urbanization processes. Although representing only 11% of the city surface, the not-urbanized blocks showed the highest species richness, which corresponded to 96.3% of the richness estimated in the city. The average species richness for most trophic groups, families, open-field or forest species and resident or migratory species decreased significantly in urbanized blocks. According to a Hierarchical Partitioning analysis the environmental variables that made the greatest positive contribution to the variation in bird species richness in urbanized blocks were the percentage of block area planned for residential use, the density of native trees and the percentage area covered by unpaved roads, whereas the commercial block density, the density of exotic trees and the percentage of block area built had the greatest negative contribution. Based on our results, policies aimed to maintain Cerrado native species in urbanized blocks would contribute to reduce bird species loss.

Elevational gradients in bird diversity in the Eastern Himalaya: an evaluation of distribution patterns and their underlying mechanisms.

BackgroundUnderstanding diversity patterns and the mechanisms underlying those patterns along elevational gradients is critically important for conservation efforts in montane ecosystems, especially those that are biodiversity hotspots. Despite recent advances, consensus on the underlying causes, or even the relative influence of a suite of factors on elevational diversity patterns has remained elusive.Methods and Principal FindingsWe examined patterns of species richness, density and range size distribution of birds, and the suite of biotic and abiotic factors (primary productivity, habitat variables, climatic factors and geometric constraints) that governs diversity along a 4500-m elevational gradient in the Eastern Himalayan region, a biodiversity hotspot within the world's tallest mountains. We used point count methods for sampling birds and quadrats for estimating vegetation at 22 sites along the elevational gradient. We found that species richness increased to approximately 2000 m, then declined. We found no evidence that geometric constraints influenced this pattern, whereas actual evapotranspiration (a surrogate for primary productivity) and various habitat variables (plant species richness, shrub density and basal area of trees) accounted for most of the variation in bird species richness. We also observed that ranges of most bird species were narrow along the elevation gradient. We find little evidence to support Rapoport's rule for the birds of Sikkim region of the Himalaya.Conclusions and SignificanceThis study in the Eastern Himalaya indicates that species richness of birds is highest at intermediate elevations along one of the most extensive elevational gradients ever examined. Additionally, primary productivity and factors associated with habitat accounted for most of the variation in avian species richness. The diversity peak at intermediate elevations and the narrow elevational ranges of most species suggest important conservation implications: not only should mid-elevation areas be conserved, but the entire gradient requires equal conservation attention.

Bird richness and composition along an agricultural gradient in New Guinea: The influence of land use, habitat heterogeneity and proximity to intact forest

Abstract We examined variation in bird species richness, abundance and guild composition along an agricultural gradient in New Guinea, and looked for any additive influence of habitat heterogeneity on these variables. The study was based on a grid of survey plots, six plots wide and 24 plots long with the long axis running from a settlement 2.4 km through active and abandoned agricultural plots towards a large area of forest. Each circular survey plot (25 m radius) was assigned to a broad habitat type, ten habitat measures taken, and birds counted for 1 h in each plot. Principal component analysis (PCA) habitat axis 1 described an axis of decreasing forest alteration (larger trees, greater tree densities, fuller canopy) that was positively correlated with distance from the settlement. Bird richness and abundance were highest at intermediate disturbance levels (plots with mid‐range axis 1 scores). Proportions of insectivores and frugivores increased with decreasing forest alteration, while proportions of nectarivores decreased. We calculated three measures of habitat heterogeneity by comparing each plot's PCA score to those of eight neighbouring plots (50–110 m away). These measures reflected how different the plot was to its neighbours, how variable the habitat was around the plot, and the degree to which the plot bordered less disturbed forest. We related these measures to plot bird variable scores independently, and to residuals following regressions of bird scores against PCA scores. Heterogeneity measures had no significant influence on abundance or richness measures, but there were greater proportions of frugivores in plots showing a given degree of habitat alteration if they bordered more pristine habitat. While we readily identified differences in bird communities along the agricultural gradient, the influences of habitat heterogeneity were not striking for birds at this fine scale.

Can oil palm plantations be made more hospitable for forest butterflies and birds?

Summary 1Rising global demand for palm oil is likely to exacerbate deforestation rates in oil palm-producing countries. This will lead to a net reduction in biodiversity unless measures can be taken to improve the value of oil palm plantations. 2Here, I investigate whether the biodiversity of oil palm plantations can be increased by determining how forest-dwelling butterflies and birds in these plantations are affected by vegetation characteristics at the local level (e.g. epiphyte prevalence) and by natural forest cover at the landscape level (e.g. old-growth forests surrounding oil palm estates). 3Across transects, vegetation variables explained 0–1·2% of the variation in butterfly species richness and 0–7% of that in bird species richness. The most important predictors of species richness across transects were percentage ground cover of weeds for butterflies; and epiphyte prevalence and presence of leguminous crops for birds. Across estates, natural forest cover explained 1·2–12·9% of the variation in butterfly species richness and 0·6–53·3% of variation in bird species richness. The most important predictors of species richness across estates were percentage cover of old-growth forests surrounding an estate for butterflies; and percentage cover of young secondary forests surrounding an estate for birds. 4Synthesis and applications. In order to maximize biodiversity in oil palm plantations, oil palm companies and local governments should work together to preserve as much of the remaining natural forests as possible by, for example, creating forested buffer zones around oil palm estates or protecting remnant forest patches in the landscape.

IS THE EFFECT OF FOREST STRUCTURE ON BIRD DIVERSITY MODIFIED BY FOREST PRODUCTIVITY

Currently, the most common strategy when managing forests for biodiversity at the landscape scale is to maintain structural complexity within stands and provide a variety of seral stages across landscapes. Advances in ecological theory reveal that biodiversity at continental scales is strongly influenced by available energy (i.e., climate factors relating to heat and light and primary productivity). This paper explores how available energy and forest structural complexity may interact to drive biodiversity at a regional scale. We hypothesized that bird species richness exhibits a hump-shaped relationship with energy at the regional scale of the northwestern United States. As a result, we hypothesized that the relationship between energy and richness within a landscape is positive in energy-limited landscapes and flat or decreasing in energy-rich landscapes. Additionally, we hypothesized that structural complexity explains less of the variation in species richness in energy-limited environments and more in energy-rich environments and that the slope of the relationship between structural complexity and richness is greatest in energy-rich environments. We sampled bird communities and vegetation across seral stages and biophysical settings at each of five landscapes arrayed across a productivity gradient from the Pacific Coast to the Rocky Mountains within the five northwestern states of the contiguous United States. We analyzed the response of richness to structural complexity and energy covariates at each landscape. We found that (1) richness had a hump-shaped relationship with available energy across the northwestern United States, (2) the landscape-scale relationships between energy and richness were positive or hump shaped in energy-limited locations and were flat or negative in energy-rich locations, (3) forest structural complexity explained more of the variation in bird species richness in energy-rich landscapes, and (4) the slope of the relationship between forest structural complexity and richness was steepest in energy-limited locations. In energy-rich locations, forest managers will likely increase landscape-scale bird diversity by providing a range of forest structural complexity across all seral stages. In low-energy environments, bird diversity will likely be maximized by managing local high-energy hotspots judiciously and adjusting harvest intensities in other locations to compensate for slower regeneration rates.

Evaluating the species energy relationship with the newest measures of ecosystem energy: NDVI versus MODIS primary production

Ecosystem energy has been shown to be a strong correlate with biological diversity at continental scales. Early efforts to characterize this association used the normalized difference vegetation index (NDVI) to represent ecosystem energy. While this spectral vegetation index covaries with measures of ecosystem energy such as net primary production, the covariation is known to degrade in areas of very low vegetation or in areas of dense forest. Two of the new vegetation products from the MODIS sensor, derived by integrating spectral reflectance, climate data, and land cover, are thought to better approximate primary productivity than NDVI. In this study, we determine if the new MODIS derived measures of primary production, gross primary productivity (GPP) and net primary productivity (NPP) better explain variation in bird richness than historically used NDVI. Moreover, we evaluate if the two productivity measures covary more strongly with bird diversity in those vegetation conditions where limitations of NDVI are well recognized. Biodiversity was represented as native landbird species richness derived from the North American Breeding Bird Survey. Analyses included correlation analyses among predictor variables, and univariate regression analyses between each predictor variable and bird species richness. Analyses were done at two levels: for all BBS routes across natural landscapes in North America; and for routes in 10 vegetation classes stratified by vegetated cover along a gradient from bare ground to herbaceous cover to tree cover. We found that NDVI, GPP and NPP were highly correlated and explained similar variation in bird species richness when analyzed for all samples across North America. However, when samples were stratified by vegetated cover, strength of correlation between NDVI and both productivity measures was low for samples with bare ground and for dense forest. The NDVI also explained substantially less variation in bird species richness than the primary production in areas with more bare ground and in areas of dense forest. We conclude that MODIS productivity measures have higher utility in studies of the relationship of species richness and productivity and that MODIS GPP and NPP improve on NDVI, especially for studies with large variation in vegetated cover and density.

The relative importance of environment, human activity and space in explaining species richness of South African bird orders

AbstractAim To assess the relative importance of environmental (climate, habitat heterogeneity and topography), human (population density, economic prosperity and land transformation) and spatial (autocorrelation) influences, and the interactions between these predictor groups, on species richness patterns of various avifaunal orders.Location South Africa.Methods Generalized linear models were used to determine the amount of variation in species richness, for each order, attributable to each of the different predictor groups. To assess the relationships between species richness and the various predictor groups, a deviance statistic (a measure of goodness of fit for each model) and the percentage deviation explained for the best fitting model were calculated.Results Of the 12 avifaunal orders examined, spatially structured environmental deviance accounted for most of the variation in species richness in 11 orders (averaging 28%), and 50% or more in seven orders. However, orders comprising mostly water birds (Charadriiformes, Anseriformes, Ciconiformes) had a relatively large component of purely spatial deviance compared with spatially structured environmental deviance, and much of this spatial deviance was due to higher‐order spatial effects such as patchiness, as opposed to linear gradients in species richness. Although human activity, in general, offered little explanatory power to species richness patterns, it was an important correlate of spatial variation in species of Charadriiformes and Anseriformes. The species richness of these water birds was positively related to the presence of artificial water bodies.Main conclusions Not all bird orders showed similar trends when assessing, simultaneously, the relative importance of environmental, human and spatial influences in affecting bird species richness patterns. Although spatially structured environmental deviance described most of the variation in bird species richness, the explanatory power of purely spatial deviance, mostly due to nonlinear geographical effects such as patchiness, became more apparent in orders representing water birds. This was especially true for Charadriiformes, where the strong anthropogenic relationship has negative implications for the successful conservation of this group.

Avian species richness and reproduction in short-rotation coppice habitats in central and western New York

Capsule Species richness and density increase rapidly with coppice age, and are similar to estimates from early successional habitats. Aim To investigate avian species richness, density and breeding success in short-rotation woody crops (SRWC) planted as potential source of renewable bioenergy. Methods We carried out regular bird censuses and systematic nest searches in dense plantations of fast-growing willow and poplar clones coppiced at three- to five-year intervals in New York, USA. Results Thirty-nine species regularly used SRWC plantations; of these at least 21 were confirmed breeding on study plots. A total of 63% of the variation in bird species richness was explained by the number of years since coppicing and plot area together. Both the richness and overall density of avian species in SRWC plots was similar to estimates obtained from the Breeding Bird Census for more typical shrublands and successional habitats (e.g. abandoned fields, second-growth forest, regenerating clearcuts). Nesting success for the most common species was within the range of values from published studies in alternative nesting habitats, although often at the lower end of the range. Brood parasitism by Brown-headed Cowbirds Molothrus ater, often an important factor in nesting success, was extremely low on the study plots. Conclusion If planted on a fairly large scale with staggered coppicing schedules, SRWC plantations would help to maintain breeding populations of birds that range from open-habitat species to woodland species. There is no evidence that conversion of substantial land area to SRWC would result in an ‘ecological trap’ for species common in the farmland–small woodland landscapes of the northeastern USA.

Determinants of bird species richness: role of climate and vegetation structure at a regional scale

SummaryWe examined the respective roles of climate and vegetation structure on geographical variation in bird species richness. The Province of Buenos Aires (central‐eastern Argentina) was divided into 146 squares of 50 km on a side. For each square we evaluated the number of bird species, the value of thirteen climatic variables, and the value of a vegetation strata index. The climatic matrix was analyzed by Principal Component Analysis (PCA), and the first factors resulting from PCA were considered as multifactorial climatic gradients. Simple and Partial Correlation Analysis among bird species richness, vegetation strata, and the first two factors derived from PCA (65% of total variation) indicated that bird richness distribution was determined by the availability of vegetation strata, associated with different vegetation types that, at the same time, were influenced by the climatic conditions summarized in the first climatic factor (a gradient of precipitation, relative humidity, annual termical amplitude, and frost occurrence). This relationships reflect the complexity of factors that can act directly as well as indirectly on the geographical patterns in species richness. Also, we evaluated the importance of study scale comparing our results with previous studies at macrogeographic and local scales, found out that the vegetation structure was the principal determinant of bird species richness at this three geographical scales.

The spatial extent and relative influence of landscape-level factors on wintering bird populations

The influences of the landscape matrix (complex of habitats surrounding a study plot) and within-patch vegetation were studied in bird communities wintering in the piedmont of Georgia, USA. Variation at the landscape and within-patch levels was controlled to reduce the likelihood of confounding and spurious relationships. The landscape matrix within 500 m of each study plot was quantified from aerial photographs. Statistical models using landscape matrix and within-patch vegetation variables explained 73–84% of variation in bird abundance and diversity among sites with landscape matrix variables accounting for 30–90% of the variation. Variation in bird species richness and diversity was explained solely by landscape variables. Models for individual species such as Carolina Wrens (Thyrothorus ludovicianus) and Rufous-sided Towhees (Pipilo erythrophthalmus) had r2 > 0.80, with the landscape matrix variables accounting for the majority of this variation. However, other species like Northern Cardinals (Cardinalis cardinalis) and White-throated Sparrows (Zonotrichia albicollis) were most strongly influenced by within-plot vegetation. The landscape influence extended beyond habitats immediately adjacent to the study plots as indicated by significant variables describing variation in more distant habitat patches. These analyses illustrate a technique for comparing the strength of within-patch versus landscape influences and measuring the spatial extent of the landscape influence in fine-grained landscapes. Report No. 3955, Environmental Sciences Division, Oak Ridge National Laboratory.