Changes in population size and genetic diversity of a raptor species occurring in the boreal forest of Saskatchewan

The American Kestrel (Falco sparverius) is one of North America's most common raptors. However, recent data reveals a decrease in the number of individuals at both migration and nesting sites, sparking concern that the North American subspecies (F. s. sparverius) may be in decline. In this study we used long-term monitoring data to examine whether a decrease observed in a study population of breeding F. s. sparverius in the boreal forests of Saskatchewan over the past two decades coincided with a loss in genetic diversity. While count data collected showed a significant decline in occupancy of nest boxes, genetic summary statistics and Bayesian modeling methods revealed evidence for a population expansion occurring in the decades directly before the start of the nest box program. The initial contradictory nature of the count and genetic data was resolved when the results examined together revealed that the detected changes in population size coincided with changes in land-use around the study site, suggesting that the shifts in numbers of F. s. sparverius may represent the subspecies' ability to respond rapidly to changes in suitable habitat. This study highlights the importance of integrating both genetic and population data into studies that examine changes in population size, especially for a migratory species where the connections between breeding sites and landscape changes may be fluid and rapid.