Desert bird associations with broad‐scale boundary length: applications in avian conservation

Abstract

Summary Current understanding regarding the effects of boundaries on bird communities has originated largely from studies of forest–non‐forest boundaries in mesic systems. To assess whether broad‐scale boundary length can affect bird community structure in deserts, and to identify patterns and predictors of species’ associations useful in avian conservation, we studied relations between birds and boundary‐length variables in Chihuahuan Desert landscapes. Operationally, a boundary was the border between two adjoining land covers, and broad‐scale boundary length was the total length of such borders in a large area. Within 2‐km radius areas, we measured six boundary‐length variables. We analysed bird–boundary relations for 26 species, tested for assemblage‐level patterns in species’ associations with boundary‐length variables, and assessed whether body size, dispersal ability and cowbird‐host status were correlates of these associations. The abundances or occurrences of a significant majority of species were associated with boundary‐length variables, and similar numbers of species were related positively and negatively to boundary‐length variables. Disproportionately small numbers of species were correlated with total boundary length, land‐cover boundary length and shrubland–grassland boundary length (variables responsible for large proportions of boundary length). Disproportionately large numbers of species were correlated with roadside boundary length and riparian vegetation–grassland boundary length (variables responsible for small proportions of boundary length). Roadside boundary length was associated (positively and negatively) with the most species. Species’ associations with boundary‐length variables were not correlated with body size, dispersal ability or cowbird‐host status. Synthesis and applications. For the species we studied, conservationists can use the regressions we report as working models to anticipate influences of boundary‐length changes on bird abundance and occurrence, and to assess avifaunal composition for areas under consideration for protection. Boundary‐length variables associated with a disproportionate or large number of species can be used as foci for landscape management. Assessing the underlying causes of bird–boundary relations may improve the prediction accuracy of associated models. We therefore advocate local‐ and broad‐scale manipulative experiments involving the boundary types with which species were correlated, as indicated by the regressions.