Master of Science
Hobson, Keith A.
Branfireun, Brian A.
Bank Swallows (Riparia riparia), a threatened species in Ontario, breed primarily in banks at lakeshores and in artificial aggregate pits. Inland pits may be ecological traps for this species, but the relative tradeoffs between these two nesting habitats are unknown. Availability of aquatic emergent insects at lakeshores may have associated nutritional benefits (e.g. Omega-3 fatty acids) and contaminants (e.g. mercury) that can directly influence juvenile growth. This study compares these breeding habitats to evaluate dietary differences as revealed by fatty acids, stable isotopes (δ13C, δ15N, δ2H), fecal DNA barcoding, and mercury. Lakeshore-nesting birds had a more aquatic emergent diet than inland birds, foraging on chironomids. Lakeshore juveniles were in better body condition than inland juveniles possibly due to a diet higher in Omega-3 fatty acids. This information is important for management decisions related to the use of inland aggregate pits by this species and conservation of suitable lakeshore nesting habitat.
Summary for Lay Audience
Bank Swallows (Riparia riparia) are a threatened songbird species in Ontario that has experienced large population declines since 1970. These birds breed primarily in banks at lakeshores or in artificial aggregate pits by burrowing into the loose soil to create their nest burrows. Inland pits may be traps for this species, meaning that birds are lured into nesting in pits which may then provide unfavourable conditions. However, the relative tradeoffs between lakeshore and pit nesting habitat are unknown. I expected that availability of aquatic emergent insects, such as midges, to be highest at lakeshore colonies with associated nutritional benefits but also more contaminants. In addition, adults molt their flight feathers on the non-breeding grounds in South America and it is currently unknown if Hg exposure is higher than on the breeding grounds. Mercury is toxic with lethal and sublethal effects, but it can be used as an indicator of diet, where aquatic foodwebs may be more elevated in mercury. I also assessed dietary differences through the combined use of markers in bird feathers known as stable isotopes, which are natural markers of diets and their origins. Fatty acids are the building blocks of fat and important nutritionally to young swallows. I can trace fatty acids to their origins using blood assays. Diet can be further described using DNA barcoding, which identifies prey items in bird feces. Ultimately, potential differences in dietary quality among nesting sites may directly influence the growth of young birds. Just as certain fatty acids are beneficial nutrients to human development, they are essential and expected to improve the growth of young birds born at lakeshores. This study compares lakeshore and inland pit breeding habitats to evaluate dietary differences by using various indicators and analyses that are complementary. Lakeshore birds had high-quality diets by feeding on midges. Furthermore, young birds at the lakeshores benefited from dietary fatty acids and were in better body condition than inland birds. Providing this information to the community may be useful in management decisions related to the use of aggregate pits by Bank Swallows and conservation of suitable lakeshore nesting habitat.
Génier, Corrine S. V., "Diet Composition and Mercury Exposure in Bank Swallows (Riparia riparia) Breeding at Lakeshore and Aggregate Pits" (2019). Electronic Thesis and Dissertation Repository. 6777.
Available for download on Saturday, August 01, 2020