Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Hobson, Keith A.

2nd Supervisor

Guglielmo, Christopher G.

Joint Supervisor

Abstract

Aerial insectivorous songbirds have been declining for decades in North America. Among many interacting factors, prey quality is important for the growth and health of nestlings. Aquatic-emergent insects provide more beneficial omega-3 fatty acids than terrestrial insects, but aerial insectivores may be able to convert shorter and less unsaturated fatty acid precursors to longer and more unsaturated chains (LC-PUFAs). Using fatty acid profiling and stable isotope techniques, I assessed the diet quality and fatty acid conversion efficiency of aerial insectivores, and using captive warblers I evaluated the incorporation of dietary LC-PUFAs into blood and the metabolism of carbohydrates versus lipids. I found that purple martin (Progne subis) and tree swallow (Tachycineta bicolor) nestlings had more aquatic-emergent diets (lower feather δ2H) than barn swallows (Hirundo rustica). As adults provision nestlings with aquatic-emergent insects, lakeshore purple martins and tree swallows had higher levels of omega-3 LC-PUFA EPA in blood plasma than inland populations. Yet, barn swallow nestlings provisioned with more terrestrial insects had among the highest levels of the omega-3 LC-PUFA DHA. Using compound-specific stable isotope analysis, I confirmed that barn swallow nestlings were able to efficiently convert fatty acid precursors into LC-PUFAs, as were purple martin nestlings. Fatty acid conversion may allow nestlings to supplement diets low in LC-PUFAs. Even with a high-quality diet, LC-PUFAs may not be equally incorporated into tissues nor metabolized. Using the yellow-rumped warbler (Setophaga coronata) as a model species, I found that plasma reflected LC-PUFAs faster than red blood cells, and that omega-3 DHA was incorporated faster than omega-6 ARA. I also confirmed that δ13C in exhaled breath can be used to distinguish between C4 and C3 dietary sources of metabolized carbohydrates and lipids. Admittedly, further understanding of fractionation of exhaled breath is needed, but studies may use this technique to trace fatty acid metabolism during nestling growth. My thesis has shown how diet quality, fatty acid conversion and incorporation can influence nutrient acquisition, indicating that birds with low conversion efficiency and poor-quality diets may be vulnerable. Wetland habitats and aquatic-emergent insects rich in LC-PUFAs may be crucial for such species.

Summary for Lay Audience

Aerial insectivores, those which feed on flying insects, have been declining for decades. Among many factors, the quality of insect prey is important to support the growth and health of young birds. Insects that emerge as adults from water supply more beneficial omega-3 fatty acids than insects that are land-based. However, aerial insectivores may also make their own fatty acids from more common fatty acids. I assessed the diet quality and the ability of aerial insectivores to convert fatty acids. I also assessed how fatty acids from the diet appear in the blood, and the use of sugars versus fats. I found that purple martins (Progne subis) and tree swallows (Tachycineta bicolor) had more aquatic diets than barn swallows (Hirundo rustica). Purple martin and tree swallow young fed aquatic insects along the lakeshore had more omega-3 fatty acids than birds inland. Yet, barn swallows fed land-based insects had among the most omega-3 fatty acids that were likely self-made. I later confirmed that barn swallows and purple martins were able to make their own fatty acids. This ability can allow young birds to cope with lacking fatty acids in their diet. Not all nutrients are equally incorporated nor used. In yellow-rumped warblers (Setophaga coronata), I found that omega-3 fatty acids from the diet appear in blood faster than other fatty acids. I also found that exhaled breath can be used to identify the source of sugars and fats. My thesis has shown that some birds may be at more risk of lacking fatty acids than others. For this reason, wetlands and their insects are important for these birds.

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