Hirundo rustica (Barn Swallows) and Tachycineta bicolor (Tree Swallows) select wetlands in agriculturally intensive landscapes, as revealed by GPS tracking

Abstract

Aerial insectivorous birds breeding in North America have experienced decades of population declines for reasons hypothesized to be related to changes in their insect prey. In agricultural landscapes, land management practices affect insect communities, leading to concerns that ongoing trends toward more intensive cultivation could affect the ability of farmland-breeding aerial insectivores to forage and provision their offspring with aerial insect prey. To understand how differences in agricultural intensity may affect the foraging behavior of different aerial insectivore species, we used GPS tags to compare the foraging movements and foraging habitat use of 2 species with different foraging ecologies, Hirundo rustica (Barn Swallow) and Tachycineta bicolor (Tree Swallow), breeding at 17 sites in agricultural landscapes in Saskatchewan, Canada. Although we identified differences in foraging behavior consistent with each species’ reported ecological traits, including T. bicolor foraging farther and over larger areas than H. rustica, overall foraging behavior was similar between species. Resource selection function analyses indicated that both species used wetlands disproportionately often relative to local wetland availability, especially when detected farther from their nests. Hirundo rustica and T. bicolor both also avoided cropped foraging habitat, using it proportionally less than it was locally available. In landscapes with greater wetland cover, both species selected for wetland habitat more strongly, and among T. bicolor, higher wetland density decreased maximum foraging distance and home range area. In contrast, we found no effect of crop cover on foraging habitat selection or foraging movements. These findings suggest that H. rustica and T. bicolor breeding in Saskatchewan agroecosystems share similar foraging strategies, with wetland habitats appearing to be highly important despite comprising only a small proportion of land area. Overall, these results indicate that protecting wetland habitats should be a priority for aerial insectivore conservation in the intensive agricultural landscapes of the Canadian prairies.