Northwest Fisheries Science Center

Rhinoceros auklet diet and productivity

Some marine bird populations in the Salish Sea (Puget Sound and the Straits of Juan de Fuca and Gerogia) are declining, but the mechanisms responsible are unclear. Rhinoceros auklets (Cerorhinca monocerata) are dependent upon this region for reproduction and are obligate piscivores. They are thus sensitive to fluctuations in forage fish populations and an ideal candidate for assessing the health of the Salish Sea ecosystem. To assess whether rhinoceros auklets are diet limited, we are comparing reproductive success and chick diet of rhinoceros auklets breeding in Washington’s inland marine waters (Protection Island) to auklets breeding on the outer Washington coast (Tatoosh Island, Destruction Island). We are comparing rhinoceros auklet reproductive performance and diet composition and quality among island colonies located in two systems (California Current and Salish Sea) differing in physical forcing mechanisms and between the 1970s and recent years. Diet diversity is lowest in the Salish Sea, intermediate on the outer coast in the California Current, and greatest at the confluence of these systems. The low interannual Salish Sea diet diversity might be considered fragile but this pattern has been stable over the past 30 years and with high reproductive success. Bill load mass and energy are similar among islands and years and appear unrelated to oceanographic conditions. Auklets maximize bill load weight and energy, which they accomplish by feeding their chicks more fish and fish species per bill load in the Salish Sea and fewer, heavier fish within the California Current. The strategies appear equivalent in terms of reproductive consequences. Burrow occupancy on Tatoosh Island was low in 2005, which was likely the result of unfavorable ocean conditions. Birds on this island experienced low fledging success in 2007, which may have been the result of high diet incidence of Pacific saury, a prey item considered to be of low quality. Burrow occupancy on Destruction Island in the California Current has been lower in recent years, a pattern consistent with recent European rabbit activity in high quality auklet habitat.


Scott F. Pearson - Wildlife Research Division, Washington Department of Fish and Wildlife Peter Hodum - Biology Department, CMB 1088, University of Puget Sound


Pearson, S. F., P. J. Hodum, T. P. Good, M. Schrimpf, and S. M. Knapp. 2013. A model approach for estimating colony size, trends, and habitat associations of burrow-nesting seabirds. The Condor 115(2): 356-365.

Pearson, S. F., P. J. Hodum, M. Schrimpf, J. K. Parrish, T. P. Good, and J. Dolliver. (in prep). Variation in seabird diet and reproduction across oceanographic regimes, time periods, and environmental conditions. Marine Ecology Progress Series.