The Bitterroot Valley Winter Eagle Project (Poster)

Abstract

Golden and Bald Eagles commonly scavenge on carrion while overwintering in Montana. This behavior may expose them to conflict with other scavengers, including other eagles. The availability of carrion is generally ephemeral, suggesting overwintering eagles must possess behavioral adaptations to successfully find food and potentially compete with other scavengers. We documented the occurrence and behavior of marked eagles at camera traps set on roadkill deer on private lands in the Bitterroot Valley of western Montana. Our re-sightings included over 25 eagles individually identifiable by wing tag, colored and numbered leg band, or satellite transmitter. We also had re-sightings of at least 10 eagles with metal USGS leg bands, allowing us to look at visitation length and behavior without individual identification. With few exceptions, most eagles visited a carcass just one day and over half of these eagles fed on the carcass once that day. The length of time a Bald Eagle feeds at the carcass increases with the number of other Bald Eagles present and reduces when Golden Eagles are present. Golden Eagles have more consistent feeding lengths regardless of the other eagles present. We also compared eagle re-sightings to movement data from eagles with transmitters to investigate whether or not persistent food availability influences the movements or behavior of Bald or Golden Eagles. Our results suggest that even with a consistent food resource, eagles generally feed then move on. This behavior may result from an adaptation to ephemeral winter food resources.