Total Bird Richness Research Articles

Breeding birds of ‘Nomentum’ nature reserve (central Italy): a forest remnant landscape surrounded by an agro-urbanized matrix

We carried out a standardized breeding bird atlas of “Nomentum” nature reserve (central Italy), located in a fragmented hilly forest near a large urbanized area (Rome). In order to obtain data about local composition, occurrence, distribution and richness, we correlated data with environmental heterogeneity and vegetation structure variables. We recorded 58 species in 48 500x500 m-wide atlas units, with Parus major, Corvus cornix, Turdus merula, Sylvia atricapilla, Sylvia melanocephala, as the most occurring in frequency (> 80%). Although synanthropic species represent only slightly more than 20% in number and urban environments are relatively reduced in size, these species show a higher mean occurrence when compared to mosaic species, despite the fact that these last are higher in species number and mosaic habitats are widely diffused. Local urbanization may disrupt communities, facilitating opportunistic species linked to these environments (i.e. synantropic) and inducing a decline in mosaic species. Moreover, the homogenization induced by anthropization could, at least partially, explain the lack of correlation between habitat diversity and species richness, at local scale. Finally, tree density and diameter do not affect total bird richness at this spatial grain/scale. In this regard, further analyses could test for possible correlations between habitat variables and single ecological guilds.

Satellite image texture captures vegetation heterogeneity and explains patterns of bird richness

Addressing global declines in biodiversity requires accurate assessments of key environmental attributes determining patterns of species diversity. Spatial heterogeneity of vegetation strongly affects species diversity patterns, and measures of vegetation structure derived from lidar and satellite image texture analysis correlate well with species richness. Our goal here was to gain a better understanding of why image texture explains bird richness, by linking field-based measures of vegetation structure directly with both image texture and bird richness. In addition, we asked how image texture compares with lidar-based canopy height variability, and how sensor resolution affects the explanatory power of image texture. We generated texture metrics from 30 m (Landsat 8) and 10 m (Sentinel-2) resolution Enhanced Vegetation Index (EVI) imagery from 2017 to 2019. We compared textures with vegetation metrics and bird richness data from 27 National Ecological Observatory Network (NEON) terrestrial field sites across the continental US. Both 30 and 10 m resolution texture metrics were strongly correlated with lidar-based canopy height variability (|r| = 0.64 and 0.80, respectively). Texture was moderately correlated with field-based metrics, including variability of vegetation height and tree stem diameter, and foliage height diversity (range |r| = 0.31–0.52). Generally, 10 m resolution texture had stronger correlations with lidar and field-based metrics than 30 m resolution texture. In univariate linear models of total bird richness, 10 m resolution texture metrics also had higher explanatory power (up to R2adj = 0.45), than 30 m texture metrics (up to R2adj = 0.31). Among all metrics evaluated, the 10 m homogeneity texture was the best univariate predictor of total bird richness. In multivariate bird richness models that combined texture with lidar-based canopy height variability and field-based metrics, both 30 m and 10 m resolution texture metrics were selected in top-ranked models and independently contributed explanatory power (up to R2adj = 46%). Lidar-based canopy height variability was also selected in a top-ranked model of total bird richness, but independently contributed only 15% of the variance explained. Our results show satellite image texture characterized multiple features of structural and compositional vegetation heterogeneity, complemented more commonly used metrics in models of bird richness and for some guilds outperformed both lidar-based canopy height variability and field-based vegetation measurements. Ours is the first study to directly link image texture both to specific components of vegetation heterogeneity and to bird richness across multiple ecoregions and spatial resolutions, thereby shedding light on habitat features underlying the strong correlation between image texture and biodiversity.

Habitat heterogeneity captured by 30-m resolution satellite image texture predicts bird richness across the United States.

Species loss is occurring globally at unprecedented rates, and effective conservation planning requires an understanding of landscape characteristics that determine biodiversity patterns. Habitat heterogeneity is an important determinant of species diversity, but is difficult to measure across large areas using field-based methods that are costly and logistically challenging. Satellite image texture analysis offers a cost-effective alternative for quantifying habitat heterogeneity across broad spatial scales. We tested the ability of texture measures derived from 30-m resolution Enhanced Vegetation Index (EVI) data to capture habitat heterogeneity and predict bird species richness across the conterminous United States. We used Landsat 8 satellite imagery from 2013-2017 to derive a suite of texture measures characterizing vegetation heterogeneity. Individual texture measures explained up to 21% of the variance in bird richness patterns in North American Breeding Bird Survey (BBS) data during the same time period. Texture measures were positively related to total breeding bird richness, but this relationship varied among forest, grassland, and shrubland habitat specialists. Multiple texture measures combined with mean EVI explained up to 41% of the variance in total bird richness, and models including EVI-based texture measures explained up to 10% more variance than those that included only EVI. Models that also incorporated topographic and land cover metrics further improved predictive performance, explaining up to 51% of the variance in total bird richness. A texture measure contributed predictive power and characterized landscape features that EVI and forest cover alone could not, even though the latter two were overall more important variables. Our results highlight the potential of texture measures for mapping habitat heterogeneity and species richness patterns across broad spatial extents, especially when used in conjunction with vegetation indices or land cover data. By generating 30-m resolution texture maps and modeling bird richness at a near-continental scale, we expand on previous applications of image texture measures for modeling biodiversity that were either limited in spatial extent or based on coarse-resolution imagery. Incorporating texture measures into broad-scale biodiversity models may advance our understanding of mechanisms underlying species richness patterns and improve predictions of species responses to rapid global change.

Landscape heterogeneity rather than crop diversity mediates bird diversity in agricultural landscapes.

Crop diversification has been proposed as farm management tool that could mitigate the externalities of conventional farming while reducing productivity-biodiversity trade-offs. Yet evidence for the acclaimed biodiversity benefits of landscape-level crop diversity is ambiguous. Effects may strongly depend on spatial scale and the level of landscape heterogeneity (e.g. overall habitat diversity). At the same time, contrasting within-taxon responses obscure benefits to specific functional groups (i.e. species with shared characteristics or requirements) if studied at the community level. The objectives of this study were to 1) disentangle the relative effects of crop diversity and landscape heterogeneity on avian species richness across five spatial scales ranging from 250 to 3000 m radii around focal winter wheat fields; and 2) assess whether functional groups (feeding guild, conservation status, habitat preference, nesting behaviour) determine the strength and direction of responses to crop diversity and landscape heterogeneity. In central Germany, 14 landscapes were selected along independent gradients of crop diversity (annual arable crops) and landscape heterogeneity. Bird species richness in each landscape was estimated using four point counts throughout the breeding season. We found no effects of landscape-level crop diversity on bird richness and functional groups. Instead, landscape heterogeneity was strongly associated with increased total bird richness across all spatial scales. In particular, insect-feeding and non-farmland birds were favoured in heterogeneous landscapes, as were species not classified as endangered or vulnerable on the regional Red List. Crop-nesting farmland birds, however, were less species-rich in these landscapes. Accordingly, crop diversification may be less suitable for conserving avian diversity and associated ecosystem services (e.g. biological pest control), although confounding interactions with management intensity need yet to be confirmed. In contrast, enhancement of landscape heterogeneity by increasing perennial habitat diversity, reducing field sizes and the amount of cropland has the potential to benefit overall bird richness. Specialist farmland birds, however, may require more targeted management approaches.

Do unpaved, low-traffic roads affect bird communities?

Unpaved, low traffic roads are often assumed to have minimal effects on biodiversity. To explore this assertion, we sampled the bird communities in fifteen randomly selected sites in Pafos Forest, Cyprus and used multiple regression to quantify the effects of such roads on the total species richness. Moreover, we classified birds according to their migratory status and their global population trends, and tested each category separately. Besides the total length of unpaved roads, we also tested: a. the site's habitat diversity, b. the coefficient of variation in habitat (patch) size, c. the distance to the nearest agricultural field, and d. the human population size of the nearest village. We measured our variables at six different distances from the bird point-count locations. We found a strong negative relationship between the total bird richness and the total length of unpaved roads. The human population size of the nearest village also had a negative effect. Habitat diversity was positively related to species richness. When the categories were tested, we found that the passage migrants were influenced more by the road network while resident breeders were influenced by habitat diversity. Species with increasing and stable populations were only marginally affected by the variables tested, but the effect of road networks on species with decreasing populations was large. We conclude that unpaved and sporadically used roads can have detrimental effects on the bird communities, especially on vulnerable species. We propose that actions are taken to limit the extent of road networks within protected areas, especially in sites designated for their rich avifauna, such as Pafos Forest, where several of the affected species are species of European and global importance.

Bird Richness and Abundance in Response to Urban Form in a Latin American City: Valdivia, Chile as a Case Study.

There is mounting evidence that urban areas influence biodiversity. Generalizations however require that multiple urban areas on multiple continents be examined. Here we evaluated the role of urban areas on avian diversity for a South American city, allowing us to examine the effects of urban features common worldwide, using the city of Valdivia, Chile as case study. We assessed the number of birds and their relative abundance in 152 grid cells of equal size (250 m2) distributed across the city. We estimated nine independent variables: land cover diversity (DC), building density (BD), impervious surface (IS),municipal green space (MG),non-municipal green space (NG), domestic garden space (DG), distance to the periphery (DP), social welfare index (SW), and vegetation diversity (RV). Impervious surface represent 41.8% of the study area, while municipal green, non-municipal green and domestic garden represent 11.6%, 23.6% and 16% of the non- man made surface. Exotic vegetation species represent 74.6% of the total species identified across the city. We found 32 bird species, all native with the exception of House Sparrow and Rock Pigeon. The most common species were House Sparrow and Chilean Swallow. Total bird richness responds negatively to IS and MG, while native bird richness responds positively to NG and negatively to BD, IS DG and, RV. Total abundance increase in areas with higher values of DC and BD, and decrease in areas of higher values of IS, SW and VR. Native bird abundance responds positively to NG and negatively to BD, IS MG, DG and RV. Our results suggest that not all the general patterns described in previous studies, conducted mainly in the USA, Europe, and Australia, can be applied to Latin American cities, having important implications for urban planning. Conservation efforts should focus on non-municipal areas, which harbor higher bird diversity, while municipal green areas need to be improved to include elements that can enhance habitat quality for birds and other species. These findings are relevant for urban planning in where both types of green space need to be considered, especially non-municipal green areas, which includes wetlands, today critically threatened by urban development.

Human impact on avian diversity in rural Mediterranean areas

Human activities influence the biodiversity of Mediterranean ecosystems and are involved in the transformation of natural habitats into farmland. We surveyed birds using the point count method on 288 plots at a 50-m radius in three altitudinal landscapes with different rural character in spring and autumn. The results showed that bird species richness in the study area was high (74 species). High total species richness was found in the upland rural landscape characterized by mixed land use and high landscape diversity. The applied richness of total, resident and Sylviidae species illustrated a definite preference for villages with a low human population during the breeding season. Positive and significant correlations were found between rural settlements and Fringillidae, Sylviidae and total bird richness at both periods in the three landscapes. Finally, a clear dependence on the land use/land cover type was shown for the five recorded priority species.

What species-specific traits make a bird a better surrogate of native species richness? A test with insular avifauna

Identification of species-specific traits that make a species a better surrogate of biodiversity is a need in order to implement successful conservation programmes in the face of limited data and resources. This study analyzes the relationship between the abundance of different surrogate species and species richness for terrestrial native avifauna of autochthonous steppe and semiarid environments in Fuerteventura Island (Spain) at different spatial grains, and explores which species-specific ecological traits (body mass, ecological density, habitat breadth, coverage of urban and agricultural environments) and conservation features (endemicity, conservation status) make a species more efficient as a surrogate. Results indicate that abundance of those surrogate species which are typically targeted by local conservation managers (according to their rarity and increase public awareness) proves to be a poor predictor of three different measures of species richness of the native terrestrial avifauna of Fuerteventura at all spatial resolutions. Nonetheless, some species were found to perform better than others according to partial least squares regression analyses applied to relate species-specific ecological traits and conservation features with correlation coefficients between abundance of each bird species and total bird richness. The best surrogates for global bird species richness are those smaller birds of medium–high abundances, broad habitat preferences, less threatened status, and with a high degree of endemicity. No scale-dependency was observed in the surrogacy power of species. Conservation planners in island scenarios should use a selection of bird species with these characteristics to identify conservation target areas in order to maximize the efficiency of surrogacy approaches.

Do miners (Manorina spp.) affect bird assemblages in continuous savanna woodlands in north‐eastern Australia?

AbstractOverabundant native species can have a significant cascading effect on other components of wildlife, and those that deplete other species, often promoted by anthropogenic change to vegetation cover and habitat, are called reverse keystone species. Birds in the genus Manorina are widely reported as being such species, and in highly disturbed or fragmented environments, and some intact environments, noisy miners Manorina melanocephala can have a strong negative effect on small passerine species via hyper‐aggressive mobbing. The tropical savannas of northern Australia consist of largely unmodified woodlands, and two species of Manorina occur naturally in this region: the noisy miner and the yellow‐throated miner Manorina flavigula. Therefore, what effect do these species have on bird assemblage in predominantly continuous habitats, relative to other typical determinants of avifauna assemblage such as vegetation structure? We used data collected from bird surveys at 511 sites across northern Queensland (179 noisy miner M. melanocephala sites, 332 yellow‐throated miner M. flavigula sites) between 1998 and 2010. We examined the variation in bird composition at each site due to increasing abundance of Manorina spp. using uni‐ and multivariate techniques. We found total bird richness was significantly lower in sites where noisy and yellow‐throated miner abundances were highest, and passerine species seemed most affected. For species, 45 species varied significantly in abundance with increasing miner numbers, and the overall effect of yellow‐throated miners on other birds seemed more pronounced. However, vegetation structure was generally an equal or more important predictor of avifauna richness and abundance. We conclude that despite the superficially intact nature of northern Australian woodlands, pastoral intensification or poor land management might create disturbances that facilitate increases in the abundance of Manorina, causing localized overabundance and a compounding negative effect on other native bird species.

BIRDS IN AGRICULTURAL MOSAICS: THE INFLUENCE OF LANDSCAPE PATTERN AND COUNTRYSIDE HETEROGENEITY

Agricultural environments are critical to the conservation of biota throughout the world. Efforts to identify key influences on the conservation status of fauna in such environments have taken complementary approaches. Many studies have focused on the role of remnant or seminatural vegetation and emphasized the influence on biota of spatial patterns in the landscape. Others have recognized that many species use diverse "countryside" elements within farmland, and emphasize the benefits of landscape heterogeneity for conservation. Here, we investigated the effect of independent measures of both the spatial pattern (extent and configuration) and heterogeneity of elements (i.e., land uses/vegetation types) on bird occurrence in farm-scale agricultural mosaics in southeastern Australia. Birds were sampled in all types of elements in 27 mosaics (each 1 x 1 km) selected to incorporate variation in cover of native vegetation and the number of different element types in the mosaic. We used an information-theoretic approach to identify the mosaic properties that most strongly influenced bird species richness. Subgroups of birds based on habitat requirements responded most strongly to the extent of preferred elements in mosaics. Woodland birds were richer in mosaics with higher cover of native vegetation while open-tolerant species responded to the extent of scattered trees. In contrast, for total species richness, mosaic heterogeneity (richness of element types) and landscape context (cover of native vegetation in surrounding area) had the greatest influence. These results showed that up to 76% of landscape-level variation in richness of bird groups is attributable to mosaic properties directly amenable to management by landowners. Key implications include (1) conservation goals for farm landscapes must be carefully defined because the richness of different faunal components is influenced by different mosaic properties; (2) the extent of native vegetation is a critical influence in agricultural environments because it drives the farm-scale richness of woodland birds and has a broader context effect on total bird richness in mosaics; (3) land-use practices that enhance the heterogeneity of farmland mosaics are beneficial for native birds; and (4) the cumulative effect of even small elements in farm mosaics contribute to the structural properties of entire landscapes.

Land use and habitat gradients determine bird community diversity and abundance in suburban, rural and reserve landscapes of Minnesota, USA

Bird species’ community responses to land use in the suburbanizing Twin Cities, Minnesota, USA, were contrasted among reserves, rural lands, and suburbs. For each land use type, bird composition, diversity, and abundance were recorded for 2 years in ≈99 plots in three sampling units (each ≈4500 ha). A habitat gradient defined by canopy structure (grasslands to savannas to forests) was influenced by land use, so ≈300 plots were used to characterize simultaneous variation in bird communities along land use and habitat gradients. At broad scales (aggregate of 33 plots covering ≈4500 ha) suburbs supported the lowest bird richness and diversity and rural landscapes the most, with reserves slightly below rural. Although reserves were like rural lands in diversity of bird communities, they supported more species of conservation concern, particularly of grasslands and savannas. Differences among land use types varied with habitat structure. Suburbs, rural lands, and reserves had similar forest bird communities, but differed in grassland and savanna bird communities. The extensive rural forests are important for the region’s forest birds. Suburban grasslands and savannas had low shrub abundance, low native bird richness and high non-native bird richness and abundance. However, total bird richness and diversity were as high in suburban as in rural and reserve plots because high native richness in suburban forests and high non-native species richness in suburban grasslands and savannas compensated for lower native richness in suburban grasslands and savannas. Bird conservation here and in the Midwest USA should protect rural forests, expand grasslands and savannas in reserves, and improve habitat quality overall.

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.

Status and habitat associations of birds on Lembata Island, Wallacea, Indonesia, with reference to a simple technique for avifaunal survey on small islands

The islands of Wallacea were surveyed most intensely by field ornithologists in the nineteenth century, and again in the 1990s. However, the status and habitat use of bird species on many islands remains unknown. This study examined birds in several natural and disturbed habitats on Lembata (also known as Lomblen) Island, Indonesia. A total of 78 bird species were recorded including six endemic to the Lesser Sundas, an additional three Wallacean endemics and a total of 27 resident forest species. Including published records, 91 bird species have been recorded for Lembata. Extrapolation from the cumulative number of new species in the 45 samples gave an expected Total Bird Richness of 103.4 species. The frequency of occurrence of Lesser Sundas endemic bird species, all Wallacean endemics and Lesser Sundas endemic subspecies, forest-dependent species and frugivores was greatest in closed canopy forest (at higher elevations). Conversely, generalist “Australo-Papuan” species, granivores and nectarivores occurred more frequently in lowlands (including human-modified habitats). Protected area proposals were made in 1982, but there has been no management of natural areas for biological conservation on Lembata. Conservation activities aiming to stem forest loss and fragmentation in an Important Bird Area in southern Lembata, which includes significant populations of the Flores Green Pigeon Treron floris (Globally Vulnerable), may be an important step. Merits of the “Species list” survey method are discussed.