Global climate change has affected flora and fauna phenology. Avian wintering areas have shifted north, migration distances have decreased, and for some species, a greater number of birds are staying year-round at breeding areas. These changes may contribute to earlier arrival time at breeding areas and advancing nesting phenology in birds. Increasing numbers of birds are nesting earlier which may be expected because warmer winters permit earlier nesting, and, for most species, it is beneficial to nest sooner because there is a strong seasonal decline in productivity. Birds that over-winter on or near breeding areas may have the advantage of early access to mates and nests compared to non-residents, and assortative mating (non-random pairing) of over-winter residents and non-residents could contribute to the advancement in nest initiation dates. Rapid population changes due to assortative mating could suggest an alternative way migratory birds respond and adapt to climate change. This research on how avian populations are responding to climate change has important implications for predicting species distribution, abundance, or persistence, and it is especially important in the case of the American kestrel (Falco sparverius), a species considered to be in decline.
My research project will address 3 questions: 1) are over-winter resident kestrels more likely to mate with other winter residents, and are non-residents more likely to mate with non-residents? 2) do over-winter resident kestrels nest earlier in the breeding season compared to non-residents? and 3) are over-winter resident kestrels genetically dissimilar from non-residents?. I will trap and mark over-winter resident American kestrels in southwest Idaho during two winter seasons (2011/12 and 2012/13), and subsequently trap mated pairs at nest boxes the following spring seasons. I will compare nest initiation dates of winter resident mated pairs and non-resident pairs, and I will use blood samples to look for genetic differences between winter resident and non-resident mated pairs and their offspring using 6 microsatellite loci.
Thesis Title: Population Response to Climate Change: Wintering Strategy has Carryover Effects on the Timing of Nest Initiation and Mate Choice in a Partial Migrant, the American Kestrel (Falco sparverius)
Abstract: The ability of a population to respond to climate change will depend on phenotypic plasticity, adaptation, or both. Bird populations have responded to warming temperatures by shifting their distributions, adjusting migration distance and timing, and breeding earlier. American kestrels (Falco sparverius) in southwestern Idaho have advanced their nesting by approximately 30 days in the last 30 years; however, the mechanisms allowing for this shift are not clearly understood. I investigated if assortative mating of wintering kestrels and non-wintering kestrels is contributing to this shift by monitoring kestrels in the winter and breeding seasons from 2010-2013. I addressed if 1) wintering kestrels nest earlier than non-wintering kestrels, 2) wintering kestrels mate with wintering kestrels and non-wintering kestrels mate with non-wintering kestrels, and 3) wintering kestrels are genetically differentiated from non-wintering kestrels. The results indicate that wintering kestrels nest earlier than non-wintering kestrels but this effect depends on year. Wintering strategy of females significantly predicted the wintering strategy of its mate which provides evidence for assortative mating. Analysis of 6 polymorphic microsatellite loci, however, gave no evidence of genetic differentiation or genetic structure between early and late breeding kestrels. This could be because there is still mixing between the groups despite differences in phenology, or assortative mating is too recent to have resulted in genetic differentiation. Overall, this study does not support assortative mating as a mechanism for the observed shifts in nesting phenology in kestrels of southwestern Idaho.
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