Intraspecific intrusion at bald eagle nests

Abstract

Competition for nesting territory has been shown to act as a density-dependent feedback mechanism influencing population growth rate. However, little is known about the nature of territorial interactions between established breeders and floaters. We examined territorial intrusion rates and associated behaviours at active Bald Eagle Haliaeetus leucocephalus nests in the lower Chesapeake Bay in 2012 and 2013. The average intrusion rate experienced at study nests during the reproductive period was 0.28 ± 0.32 intrusions/h. Variance in intrusion rate was high and there was no apparent predictive pattern to these events. Juvenile intrusions occurred closer to the nest than adult intrusions, and breeders showed higher response rates toward adults, with 78% of adult intruders eliciting a response compared to 47% of juveniles. Breeding adults responded to intruders significantly more often and more aggressively when in the presence of their mate. Further research is necessary to broadly describe the relationship between intrusion frequency and the frequency of nest failure.