Pacific Southwest

Title: Chapter 33: Offshore Population Estimates of Marbled Murrelets in California

Author: Ralph, C. John; Miller, Sherri L.

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. p. 353-360

Station ID: GTR-PSW-152

Description: We devised a method of estimating population size of Marbled Murrelets (Brachyramphus marmoratus) found in CaliforniaÂ’s offshore waters. The method involves determining the distribution of birds from the shore outward to 6,000 m offshore. Applying this distribution to data from boat surveys, we derived population estimates and estimates of sampling error. We estimate a total California population of approximately 6,500 birds (+ 450). Lower previous estimates of the Marbled Murrelet population in California were derived from surveys conducted for different purposes. Possible sources of error in our estimates are birds occurring farther offshore than our surveys, incubating birds missed while on nests, birds foraging underwater when the boat passed, double counting flushed birds, and observer error in estimating distance to birds. We feel that these sources of error compensated each other or were minimal.

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Citation

Ralph, C. John; Miller, Sherri L.   1995.  Chapter 33: Offshore Population Estimates of Marbled Murrelets in California.   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. p. 353-360.