Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Dr. Christopher G. Guglielmo

2nd Supervisor

Dr. Brian A. Branfireun

Joint Supervisor

Abstract

Mercury (Hg) is a global contaminant that persists in the environment. The organic form, methylmercury (MeHg) has been shown to adversely affect bird immune function, foraging behavior, navigation, and flight ability. Many songbirds migrate seasonally, a process that consists of multiple endurance flights and refueling at stopovers. Current knowledge of the effects of MeHg on songbird migration and survival is mostly speculative. In this thesis, I present three studies of MeHg in migratory songbirds. In Chapter 2, I assessed the breeding ground MeHg exposure (inferred from feather Hg) of 15 songbird species captured during fall migration at bird banding stations across Canada, and found exclusive insectivores had the highest feather Hg relative to partial insectivores and non-insectivores. A strong geographical trend showed that birds captured from Eastern Canada had the highest Hg exposure; nearly 2 times and 2.5 times greater than Central and Western Canada, respectively. Analysis of feather hydrogen stable isotopes suggested that birds from the northwest of Canada may experience lower Hg exposure. In Chapter 3,a captive dosing study to investigate the refueling/flight scenario with a small migratory insectivore, the Yellow-rumped Warbler (Setophaga coronata) showed that migratory birds that refuel at a highly contaminated stopover site can rapidly bioaccumulate MeHg in blood, muscles and organs within 2-weeks, and MeHg-treated birds had a reduced flight ability in a wind tunnel test. In Chapter 4, in five migratory passerine species, I compared Hg concentrations in tail feathers that were grown at or near breeding grounds prior to autumn migration and retained until the following spring. I predicted a shift in the distribution of species-specific feather Hg values towards lower means in the spring if Hg reduced survival over the migration and winter periods. The results suggest that MeHg exposure in the breeding areas could have a carry-over effect to reduce migration success and survival of insectivorous songbirds that undergo extensive and demanding migratory journeys. Together, these studies advance our knowledge of the impact of mercury on songbird migration and survival.

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