Relationships Among Migratory Behavior, Nesting Phenology, Reproductive Pace and Productivity of American Kestrels (Falco sparverius)

Spring migratory behavior can have carry-over effects on nesting phenology, potentially affecting reproductive pace and productivity. However, the relationships among these factors remain unclear. American Kestrels, the smallest falcons in North America, vary in their migratory behavior across the continent, creating excellent opportunities for comparative studies. At our study site in Southern Idaho, some kestrels migrate, while others remain resident in the region throughout the year. We examined the relationships between migratory status, nest initiation date, length of incubation and nestling periods, and rate of successful fledging in two American Kestrel populations in the Treasure Valley and Camas Prairie Centennial Marsh, Idaho. Migratory status was determined using stable hydrogen isotope analyses on claw samples taken from both parents. We collected information on phenology, pace, and productivity using trail cameras within each nest box and in-person visits. We predicted that migrant kestrels would initiate nesting later in the breeding season, have a faster pace (as seen by shorter incubation and nestling periods), and have lower productivity (i.e. fledge less offspring) compared to resident kestrels. The results of our study will provide further insight into the relationships between migratory strategy, nesting phenology, reproductive pace, and productivity in partially migratory bird populations.