Publication Date


Date of Final Oral Examination (Defense)


Type of Culminating Activity


Degree Title

Masters of Science in Raptor Biology



Major Advisor

Julie Heath, Ph.D.


James F. Smith, Ph.D.


Stephen Novak, Ph.D.


The ability of a population to respond to climate change will depend on phenotypic plasticity, adaptation, or both. Bird populations have already responded to warming temperatures by shifting their distributions, adjusting migration distance and timing, and breeding earlier. A population of American kestrels (Falco sparverius) in southwestern Idaho has advanced its nesting by approximately 30 days, on average, in the last 30 years and this has been correlated with changes in winter climate. The mechanisms allowing for this shift, however, are not clearly understood. I investigated if assortative mating of wintering kestrels and non-wintering kestrels is accompanying to this shift by monitoring kestrels in the winter and breeding seasons from 2010-2013. I asked if 1) wintering kestrels nest earlier than non-wintering kestrels, 2) wintering kestrels tend to mate with wintering kestrels and non-wintering kestrels mate with non-wintering kestrels, and 3) early breeding kestrels are genetically differentiated from late breeding kestrels. Results indicate that wintering kestrels nest earlier than non-wintering kestrels but this effect varies across years. 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 the assortative mating pattern has arisen too recently to have resulted in genetic differentiation. Overall, this study documents that there are carryover effects of wintering strategy on the timing of nest initiation and mate pairing in American kestrels. It provides evidence for assortative mating of kestrels by wintering strategy, but this assortative mating has not lead to genetic divergence in kestrels of southwestern Idaho at this time.


Karen Steenhof, M.S., was also on this graduate committee.