Avian Richness Research Articles

Variability in Energy Influences Avian Distribution Patterns Across the USA

Habitat transformations and climate change are among the most important drivers of biodiversity loss. Understanding the factors responsible for the unequal distribution of species richness is a major challenge in ecology. Using data from the North American Breeding Bird Survey to measure species richness and a change metric extracted from the MODerate resolution Imaging Spectroradiometer (MODIS), we examined the influence of energy variability on the geographic distribution of avian richness across the conterminous U.S. and in the different ecoregions, while controlling for energy availability. The analysis compared three groups of birds: all species, Neotropical migrants, and permanent residents. We found that interannual variability in available energy explained more than half of the observed variation in bird richness in some ecoregions. In particular, energy variability is an important factor in explaining the patterns of overall bird richness and of permanent residents, in addition to energy availability. Our results showed a decrease in species richness with increasing energy variability and decreasing energy availability, suggesting that more species are found in more stable and more productive environments. However, not all ecoregions followed this pattern. The exceptions might reflect other biological factors and environmental conditions. With more ecoclimatic variability predicted for the future, this study provides insight into how energy variability influences the geographical patterns of species richness.

Top predators and biodiversity: much debate, few data

Summary In two recent papers, we found support for the hypothesis of an association between the occurrence of top predators and biodiversity. Such results were recently criticized. Cabeza, Arponen & Van Teeffelen (2008) claim that the proper way to test the investigated relationship was to conduct a regional‐level complementarity analysis that pools all predators across all habitat‐types. However, such an approach may not help in assessing the performance of predators as surrogates for wider biodiversity, because: (a) management programmes on top predators almost invariably focus on a single species; (b) conservation planning and management often occur within habitats, not only across them; and (c) the required surveys and analyses may often be logistically unfeasible. Re‐analysis of our data suggests that a different methodology would not change the results. Kéry, Royle & Schmid (2008) used data from a Swiss volunteers’ monitoring scheme to claim that we missed a large number of species in our estimates of avian richness. However, we list 10 reasons why their calculations were inflated, given major differences in surface‐coverage, habitat‐sampling, field effort and in the way that secretive species were treated. Furthermore, our results for birds were replicated in analyses of butterflies and trees, which could not suffer from the same detectability biases. Roth & Weber (2008) analysed the same Swiss database and found that a group of lower‐trophic‐level species (tits) out‐performed raptors as indicators of butterfly richness (but not of bird richness). However, their analyses did not control for ecosystem identity, and data on raptor locations were of dubious quality. Furthermore, because tits are major caterpillar predators, the reported findings could have been expected on other grounds. Synthesis and applications. We disagree with Cabeza and colleagues that local studies are of limited importance. Given the paucity of available information, many more local studies are needed to check the generality of the ecological pattern we found. Until further analyses become available, polarized positions for or against top predators as biodiversity indicators are premature. Meanwhile, like any tools, top predators should be employed in conservation decision‐making with appropriate caution.

Regional variation in the historical components of global avian species richness

ABSTRACTAim Using a global data base of the distribution of extant bird species, we examine the evidence for spatial variation in the evolutionary origins of contemporary avian diversity. In particular, we assess the possible role of the timing of mountain uplift in promoting diversification in different regions.Location Global.Methods We mapped the distribution of avian richness at four taxonomic levels on an equal‐area 1° grid. We examined the relationships between richness at successive taxonomic levels (e.g. species richness vs. genus richness). We mapped the residuals from linear regressions of these relationships to identify areas that are exceptional in the number of lower taxa relative to the number of higher taxa. We use generalized least squares models to test the influence of elevation range and temperature on lower‐taxon richness relative to higher‐taxon richness.Results Peaks of species richness in the Neotropics were congruent with patterns of generic richness, whilst peaks in Australia and the Himalayas were congruent with patterns of both genus and family richness. Hotspots in the Afrotropics did not reflect higher‐taxon patterns. Regional differences in the relationship between richness at successive taxonomic levels revealed variation in patterns of taxon co‐occurrence. Species and genus co‐occurrence was positively associated with elevational range across much of the world. Taxon occurrence in the Neotropics was associated with a positive interaction between elevational range and temperature.Conclusions These results demonstrate that contemporary patterns of richness show different associations with higher‐taxon richness in different regions, which implies that the timing of historical effects on these contemporary patterns varies across regions. We suggest that this is due to dispersal limitation and phylogenetic constraints on physiological tolerance limits promoting diversification. We speculate that diversification rates respond to long‐term changes in the Earth's topography, and that the role of tropical mountain ranges is implicated as a correlate of contemporary diversity, and a source of diversification across avian evolutionary history.

Human Impacts on Regional Avian Diversity and Abundance

Patterns of association between humans and biodiversity typically show positive, negative, or negative quadratic relationships and can be described by 3 hypotheses: biologically rich areas that support high human population densities co-occur with areas of high biodiversity (productivity); biodiversity decreases monotonically with increasing human activities (ecosystem stress); and biodiversity peaks at intermediate levels of human influence (intermediate disturbance). To test these hypotheses, we compared anthropogenic land cover and housing units, as indices of human influence, with bird species richness and abundance across the Midwestern United States. We modeled richness of native birds with 12 candidate models of land cover and housing to evaluate the empirical evidence. To assess which species were responsible for observed variation in richness, we repeated our model-selection analysis with relative abundance of each native species as the response and then asked whether natural-history traits were associated with positive, negative, or mixed responses. Native avian richness was highest where anthropogenic land cover was lowest and housing units were intermediate based on model-averaged predictions among a confidence set of candidate models. Eighty-three of 132 species showed some pattern of association with our measures of human influence. Of these species approximately 40% were negatively associated, approximately 6% were positively associated, and approximately 7% showed evidence of an intermediate relationship with human influence measures. Natural-history traits were not closely related to the direction of the relationship between abundance and human influence. Nevertheless, pooling species that exhibited any relationship with human influence and comparing them with unrelated species indicated they were significantly smaller, nested closer to the ground, had shorter incubation and fledging times, and tended to be altricial. Our results support the ecosystem-stress hypothesis for the majority of individual species and for overall species diversity when focusing on anthropogenic land cover. Nevertheless, the great variability in housing units across the land-cover gradient indicates that an intermediate-disturbance relationship is also supported. Our findings suggest preemptive conservation action should be taken, whereby areas with little anthropogenic land cover are given conservation priority. Nevertheless, conservation action should not be limited to pristine landscapes because our results showed that native avian richness and the relative abundance of many species peaked at intermediate housing densities and levels of anthropogenic land cover.

Woodpeckers as reliable indicators of bird richness, forest health and harvest

Woodpeckers (family Picidae) show promise as indicators of avian diversity in forests because their populations can be reliably monitored, and their foraging and nesting activities can positively influence the abundance and richness of other forest birds. A correlation between woodpecker richness and richness of forest birds is known to exist at the landscape scale, but uncertainty remains whether this correlation occurs at the smaller stand-level spatial scales where forest management activities take place. We used data collected under a diverse range of forest types, harvest treatments, and forest health conditions during a long-term study of bird communities in interior British Columbia, Canada, to examine two basic questions: (1) at the level of individual forest stands, is woodpecker richness correlated with bird richness (measured as richness of all other bird species)? and (2) do woodpecker richness and bird richness have similar habitat correlates? Bird richness was positively correlated with woodpecker richness (β=0.59, SE=0.22, 95% CI=[0.141.03]). Richness of both woodpeckers and all other birds were positively correlated with tree species richness and negatively correlated with density of pines, and the effect for forest harvest type was similar for both measures of avian richness (uncut<partial harvest<clearcut with reserves). The effect of density of lodgepole pines killed by mountain pine beetles differed between the two richness measures, being positive for woodpecker richness and negative for forest bird richness. We conclude that the richness of woodpeckers is indeed correlated with the richness of other birds at the stand-level, and can serve as a reliable indicator of overall bird richness in most forest stands and conditions, except during insect outbreaks when differential responses by woodpeckers and the rest of the avian community may decouple the relationship between bird richness and woodpecker richness.

Assessing the impact of local habitat variables and landscape context on riparian birds in agricultural, urbanized, and native landscapes

Large tracts of natural habitat are being replaced by agriculture and urban sprawl in Mediterranean regions worldwide. We have limited knowledge about the effects of human activities on native species in these landscapes and which, if any, management practices might enhance the conservation of native biodiversity within them. Through a citizen volunteer bird-monitoring project, we compared bird abundance and species richness in northern Californian riparian zones surrounded by vineyards, urban areas, and natural areas. We assessed both local and landscape-level variables that may enhance native bird diversity in each land use type. We also demonstrate a new statistical approach, generalized estimating equations, to analyze highly variable data, such as that collected by volunteers. Avian abundance was highly correlated with both landscape context and local habitat variables, while avian richness was correlated with local habitat variables, specifically shrub richness, and percent of tree cover. In particular, shrub species richness has a strong positive correlation with riparian-preferring bird species. This suggests that active local management of riparian zones in human-dominated landscapes can increase our ability to retain native bird species in these areas.

ASSOCIATIONS OF FOREST BIRD SPECIES RICHNESS WITH HOUSING AND LANDSCAPE PATTERNS ACROSS THE USA

In the United States, housing density has substantially increased in and adjacent to forests. Our goal in this study was to identify how housing density and human populations are associated with avian diversity. We compared these associations to those between landscape pattern and avian diversity, and we examined how these associations vary across the conterminous forested United States. Using data from the North American Breeding Bird Survey, the U.S. Census, and the National Land Cover Database, we focused on forest and woodland bird communities and conducted our analysis at multiple levels of model specificity, first using a coarse-thematic resolution (basic models), then using a larger number of fine-thematic resolution variables (refined models). We found that housing development was associated with forest bird species richness in all forested ecoregions of the conterminous United States. However, there were important differences among ecoregions. In the basic models, housing density accounted for < 5% of variance in avian species richness. In refined models, 85% of models included housing density and/or residential land cover as significant variables. The strongest guild response was demonstrated in the Adirondack-New England ecoregion, where 29% of variation in richness of the permanent resident guild was associated with housing density. Model improvements due to regional stratification were most pronounced for cavity nesters and short-distance migrants, suggesting that these guilds may be especially sensitive to regional processes. The varying patterns of association between avian richness and attributes associated with landscape structure suggested that landscape context was an important mediating factor affecting how biodiversity responds to landscape changes. Our analysis suggested that simple, broadly applicable, land use recommendations cannot be derived from our results. Rather, anticipating future avian response to land use intensification (or reversion to native vegetation) has to be conditioned on the current landscape context and the species group of interest. Our results show that housing density and residential land cover were significant predictors of forest bird species richness, and their prediction strengths are likely to increase as development continues.

An indirect area effect on elevational species richness patterns

The study of elevational diversity patterns, and the attempt to disentangle the factors that create them, has proved a challenging and controversial research venue over the last few decades (Terborgh 1977, 1985, Stevens 1992, Rahbek 1995, 1997, 2005, Korner 2000, Brown 2001, Lomolino 2001, McCain 2005). Studies of elevational gradients fall into two general categories, regional studies that summarize known distributions from complete elevational bands (zones) within a defined geographical or political region, and local-scale transect studies that are based on a single survey scheme (Rahbek 1995, 2005). Elevational band area (the compiled area of each elevational zone) of a mountainous region is generally expected to decline with altitude (MacArthur 1972, Korner 2000, Lomolino 2001), although the smallest area per elevational zone can also be found at mid-elevation, where slope is sometimes steeper (Rahbek 1997). That area of regional elevational bands can influence the number of species found in each band was first clearly demonstrated by Rahbek (1997), and several studies since then have explicitly investigated this regional area effect on elevational diversity gradients (Sanders 2002, Sanders et al. 2003, Bachman et al. 2004). In recent years there has been a renewed interest in the analysis of standardized species richness data sets from transects in order to evaluate simultaneously the potential drivers of elevational diversity gradients (Md. Nor 2001, Sanchez-Cordero 2001, Grytnes 2003, Kattan and Franco 2004, Herzog et al. 2005). A number of factors such as climate-derived productivity, source-sink dynamics and the mid-domain effect, have been evaluated, and the diversity of results confirm the belief that no single factor is responsible for all observed richness patterns (Rahbek 1995, 2005, Brown 2001, Lomolino 2001, McCain 2006, Dunn et al. 2007). Most transect studies attempt to control the influence of area by sampling equal-area plots, although unstandardized plots also frequently occur (Lieberman et al. 1996, Hoffmann et al. 2001, Herzog et al. 2005). However, in addition to the direct influence of the area of the sampled plot, local communities can be perceived as dynamic samples drawn from a regional species pool (Terborgh 1973, Graves and Gotelli 1983, Cornell 1985, Ricklefs 1987). The size of the surrounding region can be thought of as a surrogate variable for the size of the regional species pool (Terborgh and Faaborg 1980, Cornell and Lawton 1992, Caley and Schluter 1997, Cornell 1999). This additional effect of area on elevational transects was, to our knowledge, first discussed by Beehler (1981), who found that a linear decrease in New Guinean forest birds on an elevational transect was paralleled by a decrease in regional area. Several other authors have suggested that regional habitat area influenced observed elevational richness patterns (Holloway 1987, Stotz 1998, Patterson et al. 1998, Brehm et al. 2003), while Heaney (2001) and Sanders et al. (2003) presented results contrasting with the hypothesis. Some recent studies have attempted to analyse this area effect quantitatively. Grytnes (2003) found that elevational band area was only correlated with site richness in two out of seven elevational gradients of plant richness in Norway. In contrast, a considerable influence from measures of surrounding habitat area has recently been demonstrated on a tropical transect measuring avian richness (Herzog et al. 2005). We will use the term indirect area effect to describe the effect of regional area on the pattern of local species richness. In an attempt to quantitatively evaluate the importance of the indirect area effect we have performed a meta-analysis on data from 71 elevational Ecography 30: 440 448, 2007 doi: 10.1111/J.2007.0906-7590.04954.x Copyright # Ecography 2007, ISSN 0906-7590

Impact of agricultural subsidies on biodiversity at the landscape level

Agricultural management is a major factor driving the change of faunal richness in anthropogenic landscapes. Thus, there is an urgent need to develop tools that allow decision-makers to understand better intended and unintended effects of agricultural policy measures on biodiversity. Here we demonstrate the potential of such a tool by combining a socio-economic model with the biodiversity model GEPARD to forecast the response of bird and carabid species richness to two scenarios of agricultural subsidies: (1) subsidies based on production levels and prices and (2) direct income support that is independent of production levels. We focussed on farmland of the Lahn-Dill area, Germany, as an example of European regions with low intensity farming. GEPARD predicts faunal richness and is based on multi-scaled resource-selection functions. Under both scenarios the area of predicted losses in species richness of birds and carabids was larger than the area of predicted gains in species richness. However, the area with predicted losses of avian richness was smaller under the direct income support scenario than under the production-based subsidy scenario, whereas the area with predicted losses of carabid species richness was smaller under the production-based subsidy scenario than under the direct income support. Yet locally, richness gains of up to four species were predicted for carabids under both scenarios. We conclude that the sometimes contrasting and heterogeneous responses of birds and carabids at different localities suggest the need for spatially targeted subsidy schemes. With the help of the GIS-based approach presented in this study, prediction maps on potential changes in local and regional species richness can be easily generated.

EFFECTS OF OLD WORLD BLUESTEM (BOTHRIOCHLOA ISCHAEMUM) ON FOOD AVAILABILITY AND AVIAN COMMUNITY COMPOSITION WITHIN THE MIXED-GRASS PRAIRIE

Various grassland bird species have displayed population declines over the past 30 to 40 years, and interest in explaining possible causes for the declines has prompted numerous studies. Many of these studies have focused on changes in agricultural practices; few have evaluated possible effects of the presence of nonnative grasses in grasslands. The objective of our study was to determine the effects a nonnative grass, Old World bluestem (OWB; Bothriochloa ischaemum), might have on grassland bird species abundance and richness, and on bird food availability (arthropod biomass). Three pastures each of native range, expired Conservation Reserve Program (CRP), and OWB were sampled from May to July 2001 in Comanche County, Kansas. Bird abundance and species richness were assessed by using a point-count method along 3 transects in each pasture. Food availability was estimated by collecting arthropods along 10 transects in each pasture by sweep-netting. Results showed significantly lower bird abundance and species richness in OWB pastures than in native pastures. OWB pastures also had significantly less arthropod biomass than native pastures. Because food availability (arthropod biomass) was directly related to percent forb cover within fields and was mostly absent in OWB pastures, we contend these were the primary factors contributing to lower avian richness and abundance in OWB fields when compared to CRP and native pastures.

Energy, range dynamics and global species richness patterns: reconciling mid‐domain effects and environmental determinants of avian diversity

Spatial patterns of species richness follow climatic and environmental variation, but could reflect random dynamics of species ranges (the mid-domain effect, MDE). Using data on the global distribution of birds, we compared predictions based on energy availability (actual evapotranspiration, AET, the best single correlate of avian richness) with those of range dynamics models. MDE operating within the global terrestrial area provides a poor prediction of richness variation, but if it operates separately within traditional biogeographic realms, it explains more global variation in richness than AET. The best predictions, however, are given by a model of global range dynamics modulated by AET, such that the probability of a range spreading into an area is proportional to its AET. This model also accurately predicts the latitudinal variation in species richness and variation of species richness both within and between realms, thus representing a compelling mechanism for the major trends in global biodiversity.

Priority Contribution. Ecology and conservation of birds in coffee plantations: a critical review

Interest in the ecology and conservation of birds in coffee plantations around the world has greatly increased since the early 1990s, especially in the Neotropical region. Much of the interest was inspired by untested hypotheses proposing that extensive conversion of traditional coffee plantations, grown under a diverse canopy of shade trees, into modern, technified plantations with severely reduced shade canopy, contributed to concurrent declines of long-distance migratory birds. This possible relationship sparked major publicity campaigns during the late 1990s and continuing today, promoting shaded coffee plantations as quality habitat for migratory birds. Based on a review of the published scientific literature concerning avian use of coffee plantations, I summarize avian ecology in coffee agroecosystems, and evaluate the hypothesis that coffee plantations are important for the conservation of migratory or resident birds. While no literature has presented strong evidence that coffee plantations in general negatively affect bird populations of conservation importance, nonetheless published studies have not tested hypotheses that birds have greater survivability, fitness or productivity in coffee plantations compared with other available habitats (natural or artificial), or that any species selects coffee plantations over other available habitats for foraging or for breeding. While coffee plantations may have higher avian richness and abundance than other highly disturbed agricultural habitats and some natural habitats, more research is needed to evaluate whether and how certain coffee agroecosystems contribute to the conservation or decline of avian diversity.

A global model of island biogeography

ABSTRACTAim The goal of our study was to build a global model of island biogeography explaining bird species richness that combines MacArthur and Wilson's area–isolation theory with the species–energy theory.Location Global.Methods We assembled a global data set of 346 marine islands representing all types of climate, topography and degree of isolation on our planet, ranging in size from 10 ha to 800,000 km2. We built a multiple regression model with the number of non‐marine breeding bird species as the dependent variable.Results We found that about 85–90% of the global variance in insular bird species richness can be explained by simple, contemporary abiotic factors. On a global scale, the three major predictors — area, average annual temperature and the distance separating the islands from the nearest continent — all have constraining (i.e. triangular rather than linear) relationships with insular bird species richness. We found that the slope of the species–area curve depends on both average annual temperature and total annual precipitation, but not on isolation. Insular isolation depends not only on the distance of an island from the continent, but also on the presence or absence of other neighbouring islands. Range in elevation — a surrogate for diversity of habitats — showed a positive correlation with bird diversity in warmer regions of the world, while its effect was negative in colder regions. We also propose a global statistical model to quantify the isolation‐reducing effect of neighbouring islands.Main conclusions The variation in avian richness among islands worldwide can be statistically explained by contemporary environmental variables. The equilibrium theory of island biogeography of MacArthur and Wilson and the species–energy theory are both only partly correct. Global variation in richness depends about equally upon area, climate (temperature and precipitation) and isolation. The slope of the species richness–area curve depends upon climate, but not on isolation, in contrast to MacArthur and Wilson's theory.

Relationships between avian richness and landscape structure at multiple scales using multiple landscapes

Little is known about factors that structure biodiversity on landscape scales, yet current land management protocols, such as forest certification programs, place an increasing emphasis on managing for sustainable biodiversity at landscape scales. We used a replicated landscape study to evaluate relationships between forest structure and avian diversity at both stand and landscape-levels. We used data on bird communities collected under comparable sampling protocols on four managed forests located across the Southeastern US to develop logistic regression models describing relationships between habitat factors and the distribution of overall richness and richness of selected guilds. Landscape models generated for eight of nine guilds showed a strong relationship between richness and both availability and configuration of landscape features. Diversity of topographic features and heterogeneity of forest structure were primary determinants of avian species richness. Forest heterogeneity, in both age and forest type, were strongly and positively associated with overall avian richness and richness for most guilds. Road density was associated positively but weakly with avian richness. Landscape variables dominated all models generated, but no consistent patterns in metrics or scale were evident. Model fit was strong for neotropical migrants and relatively weak for short-distance migrants and resident species. Our models provide a tool that will allow managers to evaluate and demonstrate quantitatively how management practices affect avian diversity on landscapes.

Post-construction Effects of an Urban Development on Migrating, Resident, and Wintering Birds

Many urban areas contain forest remnants and city parks that may be used by birds as stopover and wintering sites. We conducted a case study on how construction of a new apartment complex in Gainesville, FL, affected avian communities both in a forest site and in a portion of a marsh in an adjacent city park. In fall and winter, 1995–1999, we conducted point count surveys of migrant, resident, and wintering birds and compared 1 year of pre-construction survey data to 2 years of post-construction survey data. We conducted analyses to explore changes in: 1) abundance and richness by residency status (resident and migrant guilds), and 2) individual species abundance. Combining pre- and post-construction surveys, we sighted 71 bird species in the developed site and adjacent marsh during the fall and 46 species during the winter. Resident and migrant guild abundance and species richness were not different before versus after construction on the forest site or in the marsh for both seasons. Several individual species did decline in post-construction years, most notably the ovenbird (Seiurus aurocapillus) during the fall migration period that went from 32 to 3 sightings, pre- to post-construction. Results suggest that within the timeframe of this study, the remnant forest patch and adjacent marsh continued to attract migrating and resident species, even after development. On-site preservation of tree canopy and natural buffer areas, in combination with existing vegetative features in the surrounding landscape matrix, may explain why development had a minimal impact on avian richness and abundance.

Managed forest landscape structure and avian species richness in the southeastern US

Forest structural features at the stand scale (e.g., snags, stem density, species composition) and habitat attributes at larger spatial scales (e.g., landscape pattern, road density) can influence biological diversity and have been proposed as indicators in sustainable forestry programs. This study investigated relationships between such factors and total richness of breeding birds based on data from four studies within highly forested landscapes in the southeastern United States (Arkansas, South Carolina, and West Virginia) that were managed for commercial forest products. Habitat attributes were developed from forest inventory data and other information at the stand level and in circular buffers with radii of 250, 500 m, and 1 km around each sample point. Species accumulation curves for all study sites indicated greater richness in the youngest stands, with greater landscape age heterogeneity, and with proximity of sample points to roads. However, bird richness was not related to distance to nearest water or stream density at any scale. Pine forests had the most species at two of three sites where pine forests occurred. Stand biomass and basal area were generally not predictive of avian richness. Watersheds within the Arkansas site under more intensive management showed greater bird diversity. Overall, forest management appeared to have a positive effect on total bird richness.

Persistence of lowland rainforest birds in a recently logged area in central Java

Summary In 2001 and 2002, we assessed avian richness in Linggoasri (central Java) where almost all lowland rainforest had been cleared 3 years previously. Bird surveys were carried out in a selectively-logged forest, two regenerating forests and one pine Pinus merkusii plantation. A comparison with a bird list complied at least 3 years prior to logging in Linggoasri showed that 10 lowland bird species may have been extirpated from this area following logging. However, further surveys will be needed to validate these extirpations. A comparison with a list of lowland forest birds of Java shows that only 37% of these occurred in Linggoasri. From the lowland avifauna of Java, sole frugivores and insectivores were less likely to be present in Linggoasri. Smaller, generalist-feeding lowland species, endemic to Java, were more likely to be present in this area. Persisting lowland bird species, however, did not appear to be seriously affected physiologically by habitat degradation, showing no significant loss of body condition or reduction in survival and reproduction. There is an urgent need to preserve the few remaining lowland forest patches of Java and, given the alarming rate of deforestation throughout Southeast Asia, it is critical to conserve adequately large primary lowland forests (e.g. >5,000 ha) if we are to preserve existing lowland avifauna.

Regional land-use impacts affecting avian richness patterns in Southern Africa-insights from historical avian atlas data

Biodiversity conservation is a challenge within developing regions of the world. Landscape heterogeneity is largely directed by interconnected economic and social systems, which are largely driven by political, communal, and private control of the land estate. There is increasing evidence that areas of high species richness may coincide with dense human settlement. Influences of landscape pattern, human impact, and divergent past political land management on functional groups of bird species richness were examined in KwaZulu–Natal, South Africa. The functional groups included species of breeding, non-breeding, generalist, and specialist birds. A database of land-use/land-cover (LULCC) and human impact indicators was used to develop relationships and infer historic changes in bird richness derived from two censusing periods (1975–1979 and 1988–1992). The objective was to examine richness and compare relationships based on analyses using land management regions, avifaunal zones and socio-economic regions. Paired and two-sample t-tests documented differences in richness among land management regions and between regions over time. Landscape metrics, LULCC proportion, and other human impact variables were examined using Monte Carlo permuted multiple regressions to develop relationships for bird richness groups. Significant increases in bird group richness were shown between survey periods, as well as differences between land management regions. The statistical models explained 22–79% of variation in bird richness among avifaunal zones by functional group, and 32–99% of variation in bird richness among the socio-economic regions. The majority of the relationships were explained by LULCC proportion rather than landscape metrics denoting spatial arrangement. The analysis concludes that there have been significant increases in bird richness apparently related to land-use development during the study period. The apparent increase in richness may be due to maintenance of original vegetation-specific species in untransformed fragments in highly transformed areas combined with species that exploit transformed habitats well in the transformed areas. It is concluded that research on the interface between biogeography and human development should be seen as a perquisite for conservation assessments in developing regions of the world.

Landscape characteristics, spatial extent, and breeding bird diversity in Ohio, USA

Abstract. Avian communities are often used by ecologists as indicators of environmental decline over large spatial areas, because of the ease with which birds can be monitored by nonprofessionals and the availability of continent‐wide breeding bird data. The influence of scale on the relationship between bird diversity and the characteristics of the landscape, which can serve as proxies for decline, is receiving greater attention but is still not well understood. We combined data from the Breeding Bird Survey with landscape characteristics derived from the National Land Classification Data for Ohio, USA, to determine the effects of landscape extent on relationships between birds and landscape characteristics. These relationships were determined through previous work to be correlated with avian richness and diversity. We created areas of varying sizes using buffers around each of 58 routes, and calculated diversity for several groups of birds: all birds, five habitat guilds, and three migration guilds. The landscape extent over which landscape characteristics were considered affected the relationship between these characteristics and bird richness and diversity overall, as well as richness and diversity for several of the habitat and migratory guilds. Diversity of woodland birds, Neotropical migrants, and richness of short‐distance migrants were best explained by the landscape characteristics examined here, possibly due to a less homogeneous collection of species in the other guild groups. These results suggest that more attention is required in selecting the appropriate scale when using landscape characteristics to predict or manage avian communities, as some characteristics may be more useful for management activities over small areas versus efforts over larger areas.

Long-term consequences of habitat fragmentation—highland birds in Oaxaca, Mexico

Studies of habitat fragmentation have been restricted primarily to anthropogenically-altered habitats, with most research conducted 60–90 years post-fragmentation. It is unclear whether patterns in older systems concur with results from these dynamic landscapes, and hence the long-term viability of populations inhabiting habitat fragments remains largely unexplored. I focused on resident birds in fragments of humid pine-oak forest in Oaxaca, southern Mexico, isolated over 5000 years ago by climate-change. Seventeen fragments, ranging from 2 ha to over 150,000 ha were sampled in 1997 and 1998 yielding 141 species, of which 60 residents were used for analysis. Avian assemblages exhibited a highly nested structure and, with several notable exceptions, assemblages of birds in low-richness fragments were predictable subsets of those in more diverse fragments. Patch-scale factors—area, shape, elevation, habitat diversity and fractal dimension of edge—all exerted strong univariate influence on avian richness but were so closely inter-related that none had a significant independent effect. Thus, larger fragments were more complex in shape, included higher peaks, supported more diverse forests, and contained higher diversities of resident species. In contrast, the landscape-scale index used—distance from nearest large fragment (>50,000 ha)—had little effect on richness. This was reinforced by species-level analyses—one species was significantly influenced by isolation, compared with 31 species that displayed significant minimum-area distributions, restricted to patches larger than a particular threshold value. In terms of autecology, vagility, relative abundance and elevational breadth were closely related to distribution—those species with greater mobility, higher abundances and broader elevational tolerances were consistently more widespread. I suggest that more abundant species were less prone to extinction initially, more vagile species were better dispersers and species with broader elevational tolerances more likely to be successful colonists. As with previous research from older landscapes, patch-scale factors were consistently found to be influential, with high quality fragments supporting diverse communities regardless of landscape context. This suggests that the influence of landscape-scale factors noted in younger, anthropogenically fragmented systems may be transitory, overwhelmed by patch-scale factors with time. Which patch attributes are most influential could not be resolved, however, indicating that even thousands of years after fragmentation, they affect diversity patterns in concert. Rather than differentiating effects of area from habitat heterogeneity and other patch-level factors, I advocate resource-based approaches to understand and manage diversity in habitat fragments.