Contribution of research to management and recovery of the Roseate Tern: Review of a twelve-year project

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 40 degrees and 42 degrees N. This population was listed as end angered in the USA in 1987 because it was dangerously concentrated into a f ew 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 managemen t of the breeding colonies. This paper summarizes the results of the resear ch program and discusses the extent to which it has contributed to effectiv e management. The regional population now numbers about 4,000 breeding pair s and has been increasing slowly since 1987, except between 1991 and 1992 w hen it declined by about 17%. Noteworthy features of the demographic data c ollected since 1987 are: skewed adult sex-ratio (about 127 F to 100 M), hig h average productivity (1.0-1.2 fledglings per pair), low annual adult surv ival (0.83), and probably low survival from fledging to first breeding (abo ut 0.2). This species is a specialized forager and may be limited within th is region by the distribution of suitable feeding sites. When this regional population was listed as endangered in 1987, managers postulated that pred ation 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, fur nesting, and t hat high postfledging mortality and skewed sex-ratios are probably more imp ortant as limiting factors on population size. Research activities have con tributed both directly and indirectly to management of the regional populat ion, but it has taken longer than expected to obtain needed information on demographic parameters, causes of mortality, and other limiting factors.