Joe Corra defends MSc thesis on aerial insectivorous birds, climate, and water quality in urbanizing landscapes

STRIVE Lab MSc candidate Joe Corra presented his research the relationships among water quality, climate, and aerial insectivorous birds, and how urbanization shapes those relationships. Aerial insectivorous birds – swallows, swifts, nightjars, and flycatchers – have experienced alarming declines in North America in recent decades. Declines have occurred across this diverse guild, suggesting that the availability and quality of insect prey is a common factor. Emergent aquatic insects constitute an important prey resource for many aerial insectivorous birds, and thereby connect riparian aerial insectivores to aquatic ecosystems. For his research, Joe used the Tree Swallow (Tachycineta bicolor) to investigate the associations between aerial insectivorous birds and urbanization, climate, and water quality. Building on the research launched by the STRIVE lab in 2014, he evaluated Tree Swallow reproductive success, body condition, and trophic dynamics at seven river-riparian sites representing urban and natural/protected land use in greater Columbus, Ohio over four consecutive breeding seasons (2014-2017).

Findings: Urban sites were associated with earlier clutch initiation in the spring – urban Tree Swallows laid their eggs one week earlier than their non-urban counterparts. In addition, urban-breeding swallows had greater fledging success, with urban nests producing 1.4 more fledglings, on average, than sites in natural/protected landscapes. Body burdens of mercury were higher among nestlings at urban sites but exhibited strong interannual variability. A gradient of stream urbanization was related to greater dietary reliance by Tree Swallows on aquatic insects and aquatically-derived energy; further, urban swallows fed at higher trophic levels than did swallows at natural/protected sites.

Investigation of potential drivers suggested that multiple features of the urban environment, including higher mean temperatures, increased availability of high-quality aquatic insect prey, and fewer days of extreme cold may contribute to fledging success and influence the timing of Tree Swallow breeding in urban areas. Further, stream urbanization was related to increased reliance on aquatic resources and higher trophic position, highlighting the role of aquatic-terrestrial connectivity in urban areas. However, the potential risk from elevated aquatic contaminants in urban areas represents a potentially adverse impact for urban-breeding aerial insectivores. Overall, this research underscores the importance of water quality for terrestrial wildlife, and the results draw attention to the potential role for cities in the conservation of aerial insectivorous birds.

Adult Tree Swallow.

Joe banding a Tree Swallow.

Relationship between Urban Stream Index and Tree Swallow Trophic Position (nestlings: p < 0.0001; adults: p = 0.001).

This research was funded by the Ohio Division of Wildlife through the Ohio Biodiversity Conservation Partnership, The Columbus Zoo & Aquarium, and the National Science Foundation.

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