Does fluctuating selection maintain variation in nest defense behavior in Arctic peregrine falcons (Falco peregrinus tundrius)?

  • Author / Creator
    Gulotta, Nickolas
  • Within populations, individuals often exhibit repeatable among-individual differences in behavior, and in some cases, these are linked to different fitness outcomes. Several mechanisms have been proposed to contribute to the maintenance of repeatable among-individual variation in behavior. Here we study nest defense behavior in Arctic peregrine falcons (Falco peregrinus tundrius) over two successive breeding seasons (2018 and 2019) to evaluate the importance of three mechanisms that could underlie the maintenance of among-individual variation in this trait; state-dependence, assortative mating and fluctuating selection. Nest defense was measured as the response made by peregrines towards human observers during standard nest visits; high nest defense was characterized by close approaches to the observer, and low nest defense was characterized by maintaining greater distance from the observer. Nest defense scores ranged from 0m (i.e., contact with observer) to 600m. We found that nest defense was repeatable both within- (r = 0.37 and across-years (r = 0.19). Consistent with parental investment theory, both sexes exhibited state-dependent increases in their nest defense behavior with increasing nesting stage. Patterns of assortative mating and reproductive success varied greatly between the two study years. In the first year of the study (2018), peregrines mated assortatively; females with high levels of nest defense tended to pair with males that also had high levels of nest defense. However, the pattern reversed in 2019, and peregrines mated disassortatively. Additionally, we found that the fitness outcomes of nest defense differed between years. In 2018, peregrines with higher nest defense scores had a lower probability of fledging a nestling, and the opposite was true for 2019. Taken together, our results are consistent with fluctuating selection acting to maintain variation in nest defense behavior in peregrine falcons. We suggest that the fluctuating selection may result from an underlying trade-off between nest defense and other forms of parental investment, such as provisioning, with the overall benefit of nest defense (or provisioning) depending on year-specific environmental conditions. Although this study was only conducted over two years, they did differ markedly. The first year of the study (2018) had considerably fewer heavy rain events (N = 1), that can cause nestling mortality in this population, compared to 2019 (N = 11 heavy rain events). Consequently, there was lower overall reproductive success in 2019 compared to 2018. Future work is needed to assess the mechanism underlying fluctuating selection on nest defense in peregrine falcons.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.