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Population ecology of a migratory songbird: a full annual cycle perspective

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Title: Population ecology of a migratory songbird: a full annual cycle perspective
Author: Woodworth, Bradley Kalkman
Department: Department of Integrative Biology
Program: Integrative Biology
Advisor: Norris, D. Ryan
Abstract: Knowledge of the processes that limit and regulate animal populations throughout the annual cycle is key to understanding past population change, predicting future population trends, and implementing and achieving conservation goals. For migratory species, quantifying seasonal effects of density-dependence and density-independent factors on population dynamics has been limited by the challenge of following individuals and populations across breeding and non-breeding seasons which frequently span hundreds to thousands of kilometres. In this thesis, I combine year-round individual tracking with a 27-year population study of a migratory songbird (Savannah sparrow, Passerculus sandwichensis) on Kent Island in Canada’s Bay of Fundy, to address the question of when and where migratory species are limited and regulated during the annual cycle. In the first chapter, I examined causes and reproductive consequences of differential timing and distance of migration from three years of light-level geolocator data. This revealed the wintering grounds of the population was centered in The Carolinas, USA, with males overwintering, on average, ~275 km north of females. For males, overwintering at northern latitudes facilitated earlier arrival at the breeding grounds in spring which improved their reproductive success. In the second chapter, I evaluated effects of density and weather at the breeding and geolocator-derived wintering grounds on population growth rate (λ). I found clear support for opposing forces of winter temperature and breeding density driving variation in λ. Above-average temperatures at the wintering grounds lead to higher λ, primarily through positive effects on survival, but λ was regulated over the long-term by density-dependence of per capita female reproductive success and survival of adult males and juveniles during the breeding season. In the third chapter, I evaluated the spatiotemporal scale and reproductive traits mediating density-dependent female reproductive success at the individual-level. Female reproductive success was most strongly influenced by local neighbour density through increased nest predation and reduced double-brooding. Collectively, these results contribute to our broader understanding of where and when migratory species are limited and regulated during the annual cycle and provide insight into the individual-level and demographic mechanisms mediating responses of λ to density and density-independent factors throughout the year.
Date: 2017-05
Rights: Attribution-NonCommercial-ShareAlike 2.5 Canada
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Attribution-NonCommercial-ShareAlike 2.5 Canada Except where otherwise noted, this item's license is described as Attribution-NonCommercial-ShareAlike 2.5 Canada