Behavioral Mechanisms and Habitat Use by Birds in a Fragmented Agricultural Landscape

Abstract

Effective conservation and habitat restoration strategies in human‐dominated landscapes must be based on an understanding of the ways that habitat loss and fragmentation affect native species. We studied avian foraging behavior and patterns of occurrence in the highly fragmented agricultural landscape of the Kellerberrin district of Western Australia to better understand the factors underlying species declines and losses. We conducted three surveys of 30 wandoo woodland patches that ranged in size from 1.3 to 101.3 ha. Some patches were part of larger remnants of native vegetation, ranging in size from 3.5 to 1204.8 ha and including other habitat types. We examined the extent to which patterns of species richness, the occurrence and composition of foraging guilds, and the occurrence of individual species varied with features of woodland patches, remnants, and the surrounding landscape. Using multiple regression analyses, the best model for species richness included terms for the log of remnant area, the patch diversity of each remnant, and woodland patch condition. We delineated eight foraging guilds based on similarities in the substrate/method dimension and also using multidimensional scaling analyses. The best model for the number of foraging guilds present in a patch included a single variable representing shrub density. Analyses of nestedness based on guilds and on individual species were both significant; and for the latter, 11 of 13 species made a significant contribution to the overall pattern. We derived separate models for the occurrence of each of eight species and one guild using multiple logistic regression. Significant models included, either separately or in combination, the following variables: the log of remnant area, patch area, the total area of woodland in a remnant, and the distance to other woodland patches. For four species that had sufficient records to examine shifts in foraging behavior, we observed significant differences in both foraging methods and substrates with changes in remnant size and/or the presence of other species or guilds. Our analyses indicated that remnant area was the best single variable for measures of community structure, in part because it was strongly correlated with other variables, such as total woodland area, patch area, remnant patch diversity, number of corridor connections, and measures of isolation. For foraging guilds and for individual species, variables other than remnant area assumed greater importance. The strong patterns of nestedness for foraging guilds by remnant area may reflect the diminished availability of certain prey items in small, degraded remnants. This notion is reinforced by the relatively high species and guild richness recorded in small patches that were either fenced from grazing or embedded in large remnants. The nested pattern of species within some foraging guilds, however, indicates the importance of additional aspects of their ecology. A focus on richness alone may mask the unique responses of bird species to fragmentation and may d...

High trees increase sunflower seed predation by birds in an agricultural landscape of Israel

“…Many bird species use trees for observing, perching, foraging and roosting (Bull et al, 1992;Sonerud, 1992;Holl, 1998;Miller and Cale, 2000) and the presence of trees adjacent to crop fields may make the crops more accessible for the birds. Hence, we hypothesize that (1) habitat structures such as high trees in the surrounding of sunflower fields will increase seed predation by birds, since these structures upgrade the landscape for birds and make perching possible and foraging therefore easier; (2) seed predation increases with decreasing distance to the closest high tree (from now on termed high tree), due to reduced foraging and perching possibilities for birds; (3) the presence of high trees within a specific range influences seed predation by birds, because birds may only be able to use these trees for foraging and perching within a specific radius dependent on their visual capabilities; (4) seed predation increases with the percentage of tree cover but not with the percentage of natural habitat in the surrounding landscape, because high trees are not part of the natural habitat in our study area.…”

Habitat use and foraging behavior of male Black-and-white Warblers (Mniotilta varia) in forest fragments and in a contiguous boreal forest

“…Different tree species typically harbor different invertebrate prey, or differ in the abundance or accessibility of shared prey types (Robinson & Holmes 1982;Holmes & Schultz 1988;Adams & Morrison 1993;Whelan 2001). Other studies have reported that bird species may or may not respond to shifts in plant species composition by using different foraging tactics in different habitat settings (Franzreb 1983;Block 1990;Petit et al 1990;Miller & Cale 2000). We found that the use of aspen versus willow was the only behavior of Black-and-white Warblers that differed significantly between the two habitats, and basically mirrored tree availability (Table 2).…”

“…Nour et al 1997;Flemming et al 1999;Miller & Cale 2000) have actually compared the behavior of birds in fragments versus contiguous forest, either in terms of habitat selection or foraging, to understand the possible reasons behind the apparent failure of fragments to offer suitable habitat or compensatory responses of birds inhabiting fragments.…”

Increasing the value of bird-habitat studies in tropical forests: choice of approach and habitat measures

“…Understanding bird-habitat relationships is often a requirement of conservation studies (Bibby et al 1998), allowing us to gauge species' responses to habitat alteration (MacNally and Bennett 1997), and to predict the occurrence of species at unsurveyed sites (Miller andCale 2000, SuarezSeoane et al 2002). Bird-habitat studies at the local scale generally require detailed measurements of the physical (Pearson 1975), structural (MacArthur et al 1962), and vegetation composition or floristics (Rotenberry 1985) of sites.…”