Ideal free eagles: Bald eagle distribution patterns and use of kleptoparasitism on salmon rivers

During the autumn, migrating bald eagles (Haliaeetus leucocephalus) aggregate on coastal rivers to scavenge post-spawning salmon carcasses. In this thesis, I measured the abundance of eagles and salmon carcasses on a set of four adjacent rivers along the east coast of Vancouver Island, British Columbia. Salmon carcasses first appeared in late September, increased in abundance until mid-November, and thereafter declined. The total number of eagles tracked the temporal and spatial abundance of salmon carcasses, and generally distributed across the rivers according to the predictions of Ideal Free Distribution. I determined that the incidence of kleptoparasitism matched the distribution of eagles, and found that kleptoparasitism attempts between eagles were affected by the age of the attacker and the behavioural tactic used. Overall, my results indicate that salmon abundance affects the regional distribution patterns and use of kleptoparasitism among aggregations of foraging eagles.