Effects of Tidal Current Phase on the Distribution and Abundance of Rhinoceros Auklets (Cerorhinca monocerata) in Cattle Pass, Washington

Abstract

The distribution and abundance of Rhinoceros Auklets is related to the tide cycle. I examined the effects of tidal currents phase on the distribution and abundance of the Rhinoceros Auklets though land-based surveys of the waters within Cattle Pass, Washington. Auklets aggregated in large groups inside Cattle Pass during flooding tides. During the slack high tide numbers dropped to intermediate levels, and then declined during ebbing tides and remained very low until the next flooding tide. During flooding tides the birds aggregated in the north end of the pass where prey availability was highest. Low abundance during the ebbing tide was attributed to high prey concentrations in the south end of the pass outside of the survey area. Auklets strongly preferred the center of the pass, where the main current flowed, over the calmer water closer to shore. This study shows the importance of the tide cycle in influencing the daily movements of Rhinoceros Auklets.