As raptor populations recover following the banning of organochlorine pesticide use, there may be consequences for prey populations. While Bald Eagles (Haliaeetus leucocephalus) actively prey on Glaucous-winged Gulls and their offspring (Larus glaucescens), their presence at colonies and roost sites may also influence reproductive success of gulls by impacting activity budgets. Here we investigate changes in Bald Eagle abundance in relation to gull breeding phenology over 6 years at Seabird Rocks (Vancouver Island, Canada) and compare activity budgets of gulls in relation to Bald Eagle abundance. Bald Eagle abundance varied seasonally, peaking during late incubation and hatching of gull eggs. As Bald Eagle presence increased, gulls showed a strong increase in time allocated to vigilance (54%) and frequency of flushing (up to 6 times/hr). These results indicate that Bald Eagle attendance patterns at gull colonies coincide with hatching of gull chicks and can influence time-activity budgets of gulls. Predator-induced changes in gull behavior during the breeding season may influence reproductive success by impacting time and energy budgets and facilitating egg and chick predation. These findings could be important for understanding failure at gull colonies in Barkley Sound and evaluating impacts of increasing Bald Eagle populations in the region.
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.
Vol. 29 • No. 4