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    Author(s): Steven B. Beissinger
    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. 385-394
    Publication Series: General Technical Report (GTR)
    Station: Pacific Southwest Research Station
    PDF: View PDF  (155 KB)

    Description

    A demographic model of the Marbled Murrelet is developed to explore likely population trends and factors influencing them. The model was structured to use field data on juvenile ratios, collected near the end of the breeding season and corrected for date of census, to estimate fecundity. Survivorship was estimated for the murrelet based on comparative analyses of allometric relationships from 10 species of alcids. Juvenile ratios were generally low, and were higher for counts made from shore or in kelp beds (typically 10 percent) than conducted offshore (<5 percent). Annual survivorship was strongly related to body size in alcids. Survival for the Marbled Murrelet was predicted to be 0.845 and range to 0.90. Lambda, the expected annual growth rate of the population, was estimated for likely combinations of fecundity and survival, and indicated that under all combinations murrelet populations are expected to be declining. Based on the best data, rates of decline are predicted to be 4-6 percent per year, but the rate of decline could conceivably be twice as large. Studies in Alaska and British Columbia suggest population declines at 3-5 percent per year, supporting model predictions. Results are discussed in relation to the factors affecting murrelet population growth, and the use of juvenile ratios for monitoring murrelet populations.

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    Citation

    Beissinger, Steven B. 1995. Chapter 37: Population Trends of the Marbled Murrelet Projected From Demographic Analyses. 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. 385-394

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