Joseph Corra's Graduate Exit Seminar
Joseph will present Relationships Among Aerial Insectivorous Birds, Urbanization, Water Quality, and Climate on Thursday, December 6, 2018 at 1:00 P.M. in the Wetlands Heffner Building Room 128.
Aerial insectivorous birds – a guild comprising swallows, nightjars, swifts, and flycatchers – have experienced alarming population declines in eastern North America in recent decades. Declines across diverse species in the guild suggest that changes in flying insect prey are likely a common factor. Aerial insectivores breeding in urban areas face multiple environmental changes, as urbanization is associated with shifts in local climate, habitat structure, water quality, and both terrestrial and aquatic insect prey. Here, I investigated relationships between aerial insectivorous birds and urbanization, climate, and water quality using the Tree Swallow (Tachycineta bicolor) as a model organism. I 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). Urban nests were associated with higher fledging success and earlier laying dates. Multiple characteristics of urban sites appeared to drive patterns between swallow responses and urbanization, including differences in mean and extreme air temperatures and measures of water quality (e.g., water temperature, contaminant and nutrient concentrations). For example, higher mean air temperature was associated with earlier clutch initiation, while the frequency of extremely cold days was related to diminished fledging success. Stream urbanization was also related to greater reliance on aquatic insects, greater reliance on aquatically derived energy, and higher trophic position, and the results suggested that local-scale characteristics drove trophic responses. Overall, despite the loss of environmental quality generally attributed to cities, Tree Swallows exhibited greater reproductive success in urban settings where aquatic insects were larger, climate conditions favored egg and nestling survival, and the breeding season was longer. However, other characteristics of urban areas represent potential risks for urban-breeding aerial insectivores. Exploring the complex effects of urbanization on aerial insectivores represents an important research agenda as we continue to address declining aerial insectivore populations.