In the early 1980s, Shetland's Kittiwake population totalled 54 000 pairs in 55 breeding stations of greatly varying size. Since 1985, periodic counts of nests have been made at all stations, mostly from an inflatable boat and in the same manner as a comprehensive survey in 1981. Different stations were surveyed in different years and at varying intervals. Changes in numbers at individual stations varied in size and direction. To estimate the total breeding population, and variation in the overall rate of change between 1981 and 1997, ‘missing’ nest counts at each station were calculated from mean annual rates of change between actual counts; the overall estimated population was expressed as the annual sum of actual and calculated nest counts. Shetland's Kittiwake population declined by 50% during 1981–97. Although the decline was progressive, the rate increased markedly during 1989–93, then decreased between 1993–97. The main causes of the decline are considered to have been successive years of low breeding success, due to low availability of sandeels, increased rates of predation of nests by Great Skuas and increased predation of adults by skuas.
No takes yet. Share an insight, caveat, or question.
Heubeck et al. (1999) studied this question.