Determinants of Multiple Brooding in Barn Swallows (Hirundo rustica) in Atlantic Canada

Abstract

Multiple brooding is an important component of reproductive success in many birds and the frequency of this behaviour has been linked to intrinsic (e.g., age, experience) and extrinsic factors (e.g., weather, food availability). When extrinsic factors drive multiple brooding, it may be possible to identify conservation actions to support multiple-brooded species at risk. The Barn Swallow (Hirundo rustica Linnaeus, 1758), is a multiple-brooded aerial insectivore, currently listed as Threatened on Canada’s Species at Risk Act. We examined how weather, landcover, the presence of livestock and metal roofs (with associated heat) above nests affected the likelihood of multiple brooding in Barn Swallows nesting in Nova Scotia and New Brunswick, Canada. We found that sites with a lower proportion of open habitats, including pastures, hayfields, and lawns, within the typical foraging range (i.e., 400 m) of nests, were associated with a higher probability of multiple brooding. Also, multiple brooding may be less likely in windy conditions. We found no effect of proportion of other landcover types, weather conditions, livestock or metal roofs above nests. When possible, decreasing the proportion of open habitats around breeding sites could result in higher rates of multiple brooding, and in turn, help slow population declines.