CONSERVING PRAIRIE PONDS FOR SWALLOWS: TREE SWALLOW (TACHYCINETA BICOLOR) FORAGING AND NESTLING DIET QUALITY IN PRAIRIE AGROECOSYSTEMS
Elgin, Andrew Stephen 1994-
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Wetland ponds in the Prairie Pothole Region (PPR) of North America are foraging habitat for many avian species; however, the PPR is also agriculturally intensive and expansive, containing most of the cropland in Canada. Tree Swallows (Tachycineta bicolor), among other swallows and martins (Family Hirundinidae), forage over ponds and other aquatic habitats to exploit emergent aquatic insects as prey. Swallows may benefit from sources of aquatic insect prey, but they may incur costs, such as pesticide exposure, when foraging in landscapes dominated by cultivated cropland. I investigated the importance of ponds as foraging areas and a factor in insect prey quality for Tree Swallows nesting in prairie agroecosystems. I examined breeding female swallows’ foraging habitat selection as well as nestling swallows’ omega-3 long-chain polyunsaturated fatty acid (LC-PUFA) status and exposure to neonicotinoid insecticides – two indicators of nestling diet quality potentially influenced by prairie ponds. Based on data from GPS-tagging and a resource selection function (RSF) statistical approach, I found that female swallows more strongly selected for ponds relative to terrestrial habitats. There was a statistically significant increase in relative selection for ponds with distance from the nest, consistent with an energetic trade-off between travelling and use of more profitable foraging patches. I used the ratio of eicosapentaenoic acid (EPA, an omega-3 LC-PUFA) to arachidonic acid (ARA, an omega-6 LC-PUFA) as a qualitative dietary tracer and indicator of omega-3 LC-PUFA intake for swallows. Differences between sites in swallow erythrocyte EPA:ARA ratios were consistent with possible differences in aquatic insect biomass, unrelated to the presence of cropping. Widespread exposure to neonicotinoid insecticides was confirmed via analysis of blood plasma from nestling and adult swallows. Swallows on different study sites differed in exposure, but nestling plasma concentrations of imidacloprid were not strongly associated with amount of cropped area near nests. Nestlings hatched near cultivated cropland had greater plasma concentrations of clothianidin, on average, than those on a grassland-dominated site. Finally, an increase in nestling erythrocyte EPA:ARA ratio was associated with an increase in nestling mass, while no association between plasma total neonicotinoid concentrations and mass was detected. These results have implications for the conservation of aerial insectivores and suggest the importance of conserving and restoring prairie ponds in agroecosystems to ensure the maintenance of biodiversity in the PPR.
DegreeMaster of Science (M.Sc.)
SupervisorMorrissey, Christy A; Clark, Robert G
CommitteeJardine, Timothy D; Marchant, Tracy A; Kraus, Johanna M
Copyright DateJune 2020