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UBC Theses and Dissertations

Migration ecology of the yellow-breasted chat and gray catbird and physiology of the yellow-breasted chat Mancuso, Kristen A.


Migratory songbirds are declining in North America, and a better understanding of their full annual cycle (breeding, migration, overwintering) is important to identify potential threats and to better implement conservation initiatives. How populations are connected through different phases of the annual cycle, termed migratory connectivity, is another important conservation metric. Additionally, the identification of potential threats that may affect population persistence is important to direct conservation efforts. One less-commonly studied threat is mercury, which is a toxic heavy metal that can negatively affect neurology, reproduction, and endocrinology. Moreover, mercury may also disrupt the hypothalamic-pituitary-adrenal axis and subsequent stress response. Here, I examine the movement ecology of two migratory songbirds – the Gray Catbird (Dumetella carolinensis) and the Yellow-breasted Chat (Icteria virens). I describe migration routes, overwintering locations, and migratory connectivity. Further, I examine if mercury toxicity and its associated effects on the stress response is a potential threat to Yellow-breasted Chat populations throughout their breeding range. To answer questions about migration ecology, I use GPS tags, geolocators, genetics, stable hydrogen isotopes, and bird banding encounter data. To answer questions about conservation physiology, I measured mercury and corticosterone levels in chat feathers. I found that breeding Gray Catbirds in British Columbia and Montana migrate eastward and then southward to overwintering locations in northeastern Mexico and Texas. Individuals from both populations overlapped during the overwintering period; a case of weak migratory connectivity. I found that Yellow-breasted Chats in British Columbia migrate south to overwintering locations in western Mexico. However, other breeding populations also appear to overwinter in western Mexico, suggesting weak migratory connectivity. From my physiology analyses, I found that mercury levels in feathers were relatively low, 0.30 ± 0.02 µg/g, and mostly considered background levels across the chat breeding range. There was no correlation between mercury and corticosterone levels, suggesting that mercury was not affecting the activity of the hypothalamus-pituitary-adrenal axis. The results of my research elucidate key details of the full annual cycle for Gray Catbirds and Yellow-breasted Chats and indicate little threat of mercury toxicity and subsequent endocrinology malfunction to Yellow-breasted Chats.

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