Endogenous biomarkers reveal diet partitioning among three sympatric species of swallows

Since the early 1990s, aerial insectivorous birds have shown serious population declines in North America, but it is not clear if factors common to all species within this guild account for these declines. Among sympatric swallows, population trends differ, and this may be due to differences in ecology operating throughout the annual cycle. Although these species all feed on aerial insects, prey taxa can differ tremendously in their aeroecology and use by swallows. We examined the potential for dietary differences among three species of swallows, Barn Swallow (Hirundo rustica), Cliff Swallow (Petrochelidon pyrrhonota), and Tree Swallow (Tachycineta bicolor), breeding sympatrically in southern Ontario, Canada. Potential interspecific differences in nestling diet were examined using two endogenous biomarkers, DNA barcoding of nestling feces and stable isotope analysis (delta H-2, delta C-13, delta N-15) of nestling feathers. We found evidence for differences in dietary sources of provisioned young where Barn Swallows provisioned more terrestrial-based prey, Cliff Swallows provisioned an intermediate diet, and Tree Swallows the most aquatic-emergent insect diet. We suggest this information may help to identify potential factors contributing to differential declines of aerial insectivores operating on the breeding grounds, including diet quality.

Automated summary

Research has found that among three species of swallows breeding sympatrically in southern Ontario, Canada, Barn Swallows provisioned more terrestrial-based prey, Cliff Swallows provisioned an intermediate diet, and Tree Swallows provided the most aquatic-emergent insect diet, indicating potential factors contributing to differential declines of aerial insectivores on the breeding grounds.