Natural and human-made nesting habitat use by Bank Swallow (Riparia riparia) in Canada

Bank Swallow (Riparia riparia) is a Threatened migratory bird in Canada that nests colonially in burrows excavated in both human-made and natural banks. Until the mid-20th century, nest record cards reported 60% of Bank Swallows in Canada nested in human-made habitats. Here we provide an update on the proportion of Bank Swallow nesting colonies in natural and human-made habitats in Canada’s provinces and territories based on data from a variety of sources including breeding bird atlases and eBird. Bank Swallow nesting colonies reported from 2001 to 2017 throughout Canada indicate a reversal in the dominant type of habitat used for nesting, with a 56% probability that nesting occurrences are now found in natural habitats. We discuss possible mechanisms responsible for the apparent reversal and recommend that natural nesting habitat be formally protected and restored where it has been altered, especially where co-benefits include climate change resiliency. With the support of landowners and industry, active colonies in human-made habitats will likely make an important contribution to a resilient Bank Swallow population, the majority of which presently appears to nest in natural habitats across the country.