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Aerial Insectivorous Birds Linked to Water Quality and Climate in Urbanizing Landscapes

Corra, Joseph William

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2019, Master of Science, Ohio State University, Environment and Natural Resources.
Aerial insectivorous birds – a guild comprising swallows, nightjars, swifts, and flycatchers -- have experienced alarming population declines in eastern North America in recent decades. Although declines in individual bird species may be linked to other causes, including loss or fragmentation of suitable breeding habitat and habitat degradation in tropical wintering grounds, similar declines across multiple, taxonomically diverse species in the guild indicate that changes in flying insect prey is likely a common factor. Aerial insectivores breeding in urban areas -- comprising 69.4 million acres (3.6% of total) in the contiguous United States and continuing to expand -- are affected by multiple environmental changes, including alterations to local climate, habitat structure, and water quality, as well as potential shifts in both terrestrial and emergent aquatic insect prey. Emergent aquatic insects have recently been shown to provide energetic advantages to aerial insectivorous birds relative to terrestrial insects, yet they are highly sensitive to changes in water quality. Here, I used the Tree Swallow (Tachycineta bicolor) to investigate potential associations between aerial insectivorous birds and urbanization, local climate, and water quality. Specifically, 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). Study sites with impervious surface in the watershed >25% were classified as urban. Urban nests were associated with higher fledging success (linear mixed-effects model [LMM]: p = 0.009) and earlier clutch initiation (LMM: p = 0.060). Nestling mass was not related to land use (LMM: p = 0.930) but exhibited high interannual variability (LMM: p = 0.006), as did body condition in adult males (LMM: p = 0.010), and mercury (Hg) in both adults (LMM: p = 0.080), and nestlings (LMM: p < 0.001). The interaction of year x land use also had a significant influence on nestling Hg (LMM: p < 0.001). I also used an Urban Stream Index (USI) to explore potential relationships between continuous measures of stream urbanization (e.g., nutrient concentrations, riparian canopy cover, water temperature) and swallow reproductive success and body condition and found that the USI was related to greater fledging success (R2 = 0.16, p < 0.001). 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, nutrient concentrations, turbidity). For example, higher mean air temperature was associated with earlier clutch initiation (R2 = 0.06, p = 0.039), while the frequency of extremely cold days was related to diminished fledging success (R2 = 0.14, p = 0.003). Relative to trophic position, I investigated the relationships between urbanization and Tree Swallow reliance on aquatically derived energy (i.e., originating from aquatic primary production) and trophic position. Bayesian mixing models using 13C and 15N isotopes showed that nutritional reliance on both aquatic primary production and aquatic insects had significant interannual variability. Reliance on aquatic insects by nestling swallows exhibited a significant interaction of year × land use (LMM: p < 0.001), suggesting a possible relationship between elevated total N in the water column and aquatic insect consumption. Trophic position of adult swallows was 8.3% higher at urban than at natural/protected sites (LMM: p = 0.020), whereas nestlings exhibited high interannual variability in trophic position (LMM: p < 0.001), but were not related to land use (LMM: p = 0.720). My results for reliance on aquatic insects, aquatically derived energy, and trophic position all revealed a strong random effect of site, suggesting that local-scale water chemistry and land-use/land-cover characteristics may play a prominent role in shaping flying insect assemblages and driving aquatic-terrestrial energetic pathways. Supporting this finding, I also observed strong relationships between the USI and swallow trophic dynamics: USI was related to greater reliance on aquatic insects among both adult and nestling swallows (adults: R2 = 0.10, p = 0.036; nestlings: R2 = 0.23, p < 0.001), greater reliance on aquatically derived energy (adults: R2 = 0.14, p = 0.019; nestlings: R2 = 0.20, p < 0.001), and higher trophic position (adults: R2 = 0.23, p = 0.001; nestlings: R2 = 0.22, p < 0.001). 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, local climate conditions favored egg and nestling survival, and the breeding season was longer. However, the chronic effect of elevated Hg body burdens in urban areas represents a potentially adverse impact for urban-breeding aerial insectivores. For trophic measures, gradients of urbanization appeared to mediate nutritional reliance on aquatic resources and trophic position more strongly than did a coarser, categorical classification of urbanization. Aerial insectivore energetics may have important implications for long-term population trends as related to fitness, migration survival, exposure to contaminants, and reproductive success. However, owing to differences in foraging strategy, nesting strategy, and dietary preferences, the responses of other aerial insectivorous species to urbanization may vary. Determining the composite effects of urbanization on aerial insectivores represents an important research agenda as we continue to address declining aerial insectivore populations.
Mažeika Sullivan (Advisor)
Stephen Matthews (Committee Member)
Rachel Gabor (Committee Member)
257 p.

Recommended Citations

Citations

  • Corra, J. W. (2019). Aerial Insectivorous Birds Linked to Water Quality and Climate in Urbanizing Landscapes [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546608385733753

    APA Style (7th edition)

  • Corra, Joseph. Aerial Insectivorous Birds Linked to Water Quality and Climate in Urbanizing Landscapes. 2019. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1546608385733753.

    MLA Style (8th edition)

  • Corra, Joseph. "Aerial Insectivorous Birds Linked to Water Quality and Climate in Urbanizing Landscapes." Master's thesis, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546608385733753

    Chicago Manual of Style (17th edition)