Pacific Southwest

Title: Chapter 32: Distribution and Population Estimates of Marbled Murrelets at Sea in Oregon During the Summers of 1992 and 1993

Author: Strong, Craig S.; Keitt, Bradford S.; McIver, William R.; Palmer, Clifford J.; Gaffney, Ian

Date: 1995

Source: In: Ralph, C. John; Hunt, George L., Jr.; Raphael, Martin G.; Piatt, John F., Technical Editors. 1995. Ecology and conservation of the Marbled Murrelet. Gen. Tech. Rep. PSW-GTR-152. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; p. 339-352

Station ID: GTR-PSW-152

Description: We used standardized transect techniques to count Marbled Murrelets and other seabird species at sea from a boat and from a low-flying light aircraft along the length of the Oregon coast. The focus of effort was on vessel surveys of the central Oregon coast. In both years, Marbled Murrelets were most abundant in central Oregon, between Cascade Head and Cape Arago. They were concentrated much closer to shore in 1992 than in 1993. Different distribution patterns in the two years was likely a consequence of El Niño oceanographic conditions which severely impacted OregonÂ’s seabirds in 1993. New population estimates for the state ranged from 2,500 (shore-based) to 22,250 birds (boat). Estimates generated from vessel surveys were considered far more reliable than estimates from air or from shore counts due to more thorough coverage, proximity to birds, more observers, and longer scanning time. Vessel estimates using both strip and line transect analyses for two years with very different distribution characteristics each produced state population totals between 15,000 and 20,000 birds, after accounting for some assumptions. There is a strong possibility that a large proportion of these birds may not be nesting successfully due to limitations of nesting habitat and other factors.

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Citation

Strong, Craig S.; Keitt, Bradford S.; McIver, William R.; Palmer, Clifford J.; Gaffney, Ian  1995.  Chapter 32: Distribution and Population Estimates of Marbled Murrelets at Sea in Oregon During the Summers of 1992 and 1993.   In: Ralph, C. John; Hunt, George L., Jr.; Raphael, Martin G.; Piatt, John F., Technical Editors. 1995. Ecology and conservation of the Marbled Murrelet. Gen. Tech. Rep. PSW-GTR-152. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; p. 339-352.