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 (δ 2H, δ 13C, δ 15N) 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.

Smaller brained cliff swallows are more likely to die during harsh weather

The cognitive-buffer hypothesis proposes that more harsh and unpredictable environments favour animals with larger brains and resulting greater cognitive skills. Comparisons across taxa have supported the hypothesis, but it has rarely been tested within a species. We measured brain size, as inferred from head dimensions, for 1141 cliff swallow specimens collected in western Nebraska, 1982–2018. Cliff swallows starving to death during unusual late-spring cold snaps had significantly smaller brains than those dying from other causes, suggesting that brain size in this species can affect foraging success and that greater cognitive ability may confer advantages when conditions exceed normal environmental extremes. Brain size declined significantly with the size of the breeding colony from which a specimen came. Larger brains may be favoured in smaller colonies that represent more unpredictable and more challenging social environments where there is less public information on food sources and less collective vigilance against predators, even in relatively normal conditions. Our results provide intraspecific support for the cognitive-buffer hypothesis and emphasize the potential evolutionary impact of rare climatic events.

Feather mites of the genus Trouessartia Canestrini (Acariformes: Trouessartiidae) from swallows (Passeriformes: Hirundinidae) in Canada

Seven species of the feather mite genus Trouessartia Canestrini, 1899 (Astigmata: Trouessartiidae) have been recorded on swallows and martins (Passeriformes: Hirundinidae) in Manitoba (Canada). Of them, five are described as new species: Trouessartia ampulicaudata sp. n. and T. petrochelidon sp. n. from the American cliff swallow Petrochelidon pyrrhonota (Vieillot), T. bochkovi sp. n. from the tree swallow Tachycineta bicolor (Vieillot), and T. cryptocaudata sp. n. and T. progne sp. n. from the purple martin Progne subis (Linnaeus). A new species group stelgidopteryx, incorporating Trouessartia species living on hirundinids of the genera Progne, Tachycineta and Stelgidopteryx, is established. Renewed diagnoses of four Trouessartia species groups (appendiculata, crucifera, minutipes, and stelgidopteryx) restricted to hirundinids and a key to species recorded so far and potentially expected on swallows of North America are proposed. Host associations of Trouessartia species with swallows in North America are briefly discussed.