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Black bear (Ursus americanus) population dynamics on Long Island in Willapa Bay, Washington, were monitored between 1973 and 1982. The population apparently grew from a small nucleus of bears present after major logging efforts stopped in 1968 to a peak of 33-36 bears over 1 year of age in 1975-76. Twenty-two bears remained on the island in the spring of 1982. Successional changes in plant communities in clear-cut areas altered their food value to bears through this period. By 1976 female progeny were generally no longer accepted into the breeding population and population productivity began to decline. Each of 5 radio-collared adult females raised young to 9 months of age in 1974 or 1975, whereas only 3 of 11 were successful in 1981 or 1982. Observations of marked bears and ages of trapped bears also documented the decline in production. By 1980 some resident bears began to include parts of the mainland in their home areas. Changes in size, productivity, and behaviors of this population illustrate the mechanisms employed by black bears in response to ephemeral habitats.