Brandt's cormorants can flush off of their nests when boaters approach too closely or park visitors enter closed areas at Alcatraz Island. When the attending parent leaves the nest, predatory western gulls often come in and eat eggs or nestlings. Because Brandt’s cormorants and most of the waterbirds on Alcatraz are nest in colonies and often share communal behaviors for the benefit of the entire group, whole groups of birds tend to flush from nests when a single bird reacts to a disturbance.