Nesting Ecology of the Barn Swallow on Agricultural Lands in Yukon

Since the 1980s, the abundance of the Barn Swallow (Hirundo rustica) in North America, including the far north, has declined. To better understand the species’ biology north of 60° N, near the northern limit of its range, and in a region of expanding agriculture, we studied its nesting ecology on farms in southern Yukon Territory, Canada, in 2019 and 2020. We followed 21 attempted nests in 2019, 20 in 2020, of which 52% and 60%, respectively, were inside buildings with permanently open entrances. Other nests were built on the outside of buildings. In both years we inferred successful double brooding by three pairs, which is rarely reported north of 60°N latitude. We found the swallows’ reproductive output to be similar to that at temperate latitudes: first clutches ranged from three to six eggs (mean 4.8 in 2019; 4.2 in 2020); second clutches may have averaged marginally smaller (n = 6). The mean number of fledglings per nest was 3.3 in 2019 and 3.0 in 2020. Twenty-one percent of nests failed, either by falling off a vertical substrate or because of predation by deer mice (Peromyscus spp.), Black-billed Magpies (Pica hudsonia), or domestic cats. We also compared the air temperatures at nests, usually near building roofs, to ambient temperatures, finding them on average 1.6°C warmer than temperatures outside buildings. We set out 33 platforms and 20 wooden cups designed for Barn Swallow nesting but over the two years of our study the birds did not use any of them.