Habitat Use by Steller Sea Lions (Eumetopias jubatus), Harlequin Ducks (Histrionicus histrionicus), and Black Oystercatchers (Haematopus bachmani) at Cattle Pass, Washington

Abstract

Two studies were conducted at Cattle Pass, Washington between 13-18 August 2014. The first study was conducted to determine the relationship between tidal height and the haul-out abundance of Steller Sea Lions (Eumetopias jubatus) at the Whale Rocks of the San Juan Channel. There was a clear diurnal pattern of abundance during both of the days used for data analysis. The abundance was very low in the morning which may be a result of the nighttime/early morning foraging behavior characteristic of Steller Sea Lions. It was determined that this variation in haul-out abundance of Steller Sea Lions did not occur in response to changes in tidal height. The data also suggest that air temperature may play a role in determining the total abundance of Steller Sea Lions. The second study was done to understand how two unrelated bird species, Harlequin Ducks (Histrionicus histrionicus) and Black Oystercatchers (Haematopus bachmani), compare and contrast in their use of the Cattle Pass rocky intertidal habitat post-breeding season. It was found that Black Oystercatchers spend most of their time loafing in the region while Harlequin Ducks spend most of their time swimming and foraging. These data suggest that Black Oystercatchers use the habitat primarily as a resting area between flock feedings while Harlequin Ducks use it primarily as a feeding ground during molting periods that cause them to be temporarily flightless.