Contribution of Research to Management and Recovery of the Roseate Tern: Review of a Twelve-Year Project

Abstract

-The Northwest Atlantic population of the Roseate Tern (Sterna dougallii) is largely confined to a small breeding area along the northeast coast of the USA between 400 and 420N. This population was listed as endangered in the USA in 1987 because it was dangerously concentrated into a few breeding sites (85% on two islands in the 1980s). The nesting population in the area from Long Island, New York to Cape Cod, Massachusetts has been studied intensively since 1987, in conjunction with a program of management of the breeding colonies. This paper summarizes the results of the research program and discusses the extent to which it has contributed to effective management. The regional population now numbers about 4,000 breeding pairs and has been increasing slowly since 1987, except between 1991 and 1992 when it declined by about 17%. Noteworthy features of the demographic data collected since 1987 are: skewed adult sex-ratio (about 127 F to 100 M), high average productivity (1.0-1.2 fledglings per pair), low annual adult survival (0.83), and probably low survival from fledging to first breeding (about 0.2). This species is a specialized forager and may be limited within this region by the distribution of suitable feeding sites. When this regional population was listed as endangered in 1987, managers postulated that predation and displacement by gulls were important factors limiting numbers and productivity. Research since 1987 has suggested that the primary effect of gulls is to limit the number of secure sites available for nesting, and that high postfledging mortality and skewed sex-ratios are probably more important as limiting factors on population size. Research activities have contributed both directly and indirectly to management of the regional population, but it has taken longer than expected to obtain needed information on demographic parameters, causes of mortality, and other limiting factors. Received 5 February 1999, accepted 18 April 1999.