Effects on Incubation Behavior in American Kestrels

Incubation and parental care are essential behaviors for the healthy development of offspring. Stressors such as migration and disease can affect parental care resulting in altered egg survival and hatch rates. Therefore, varying individual fitness and life history events may lead to changes in reproductive fitness across a population. We examined the relationship between incubation behavior and blood parasite prevalence, migratory strategy (migrant or resident), mass, and first egg date in a population of American Kestrels (Falco sparverius) in southwest Idaho to determine influences on incubation behavior. We observed incubation behavior using nest box camera images taken during preset daylight times. Individual migration status was determined using stable hydrogen isotope analysis on claw samples taken during the time of breeding. We predicted that stressors would negatively affect incubation behavior, leading to an adult that is not displaying appropriate parental care. We discovered that American Kestrels in southwest Idaho showed a common pattern in incubation behavior, with males incubating for an average of 26.3% and females for 59.1% of the total incubation period, and the eggs were uncovered for 14.6% of the time. Incubation was heavily dependent on female incubation, with the only factor significantly affecting male incubation being female incubation (p < 0.0001). However, female incubation was significantly affected by date of first egg laid (p = 0.02), relative parasite load (p = 0.03), and male incubation (p < 0.0001). There was no effect of migration strategy or nesting phenology on incubation behavior. The relationship between parasite load and female incubation shows a positive correlation, suggesting the stressors of a parasite infection possibly inhibit hunting and defense behaviors, leading to a greater proportion of time inside the nest box. These results will provide further insight into the relationships between incubation behavior and stress in bird populations of southwest Idaho.