Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Master of Science




Hobson, Keith A.


Barn Swallows (Hirundo rustica), Cliff Swallows (Petrochelidon pyrrhonota) and Tree Swallows (Tachycineta bicolor) breed sympatrically in southern Ontario but it is unclear how these species differ ecologically, and their coexistence implies niche segregation. I investigated potential interspecific differences in nestling diet and post-fledging movements. Using DNA barcoding of nestling feces and stable isotope analysis (δ13C, δ15N, δ2H) of nestling feathers, I found evidence of differences in dietary sources of provisioned young. Barn Swallows showed evidence of provisioning more terrestrial-based prey, Cliff Swallows provisioned an intermediate diet, and Tree Swallows the most aquatic-based diet. To determine post-fledging movements, fledglings were tracked using automated telemetry.Cliff Swallow fledglings differed from the other two species in their post-fledging residency time at the natal site. This information may help to identify potential factors contributing to differential declines operating on the breeding grounds.

Summary for Lay Audience

Rehabilitating populations of threatened species often requires an understanding of the interactions of those species with others in the community. When closely related or similar species occupy the same habitat, it is expected they use resources in slightly different ways which reduces competition. Aerial insectivores are migratory birds which catch and eat flying insects. These birds’ populations have been declining throughout North America. Evidence suggests that the time from hatching until migration is a vulnerable period and might affect aerial insectivore population trends. My study investigated three species of aerial insectivores which can be found breeding in the same area in southern Ontario. Typically, Barn Swallows, Cliff Swallows, and Tree swallows can be found nesting in agricultural areas. Since these three species share their habitat and diet, I predicted there would be key differences among them which facilitated coexistence. I looked specifically at the diet of nestlings, as well as movements of young once they left the nest. This has been documented to be an important stage, and so any differences might give insights into differential population declines. Nestling diet was determined by extracting insect DNA from the nestlings’ feces and comparing the results to a DNA database. Stable-isotopes were also used to determine diet. Stable isotopes of an element have varying atomic mass, molecules containing heavier stable isotopes will move slower than their lighter counterpart. These isotopes vary across the environment in predictable ways and are integrated into animal tissues from their diet. I determined that the three species are feeding different prey to their young. I tracked movements of the young by outfitting them with a radio-transmitter which could be detected by automated receiving towers that are located across southern Ontario. I found that Cliff Swallows that hatch later in the season significantly decrease the time spent in their natal area compared to Barn and Tree swallows.