Changing balance between survival and recruitment explains population trends in Red Knots Calidris canutus islandica wintering in Britain, 1969-1995

Abstract

recruitment explains population trends in Red Knots Calidris canutus islan-dica wintering in B ritain, 1969-1995. Ardea 89(2) : 301-317. The demography of Red Knots Calidris canutus islandica wintering in Britain from 1969 to 1995 was examined using published data on winter numbers, unpub li shed ringing data, and information on the percentages first year birds in late autumn and winter (defined here as 'recruitment'). The maximum time between ringing and reporting was 24 years for a Red Knot ringed as an adult. The mortality rate of juveniles during their first winter was four times that of adults, but did not differ later. For three periods, recruitment minus mort ality corresponded qualitatively with changes in population size. In 1969-77, when the numbers wintering in B ritain were declining by 8.7 % annually, the me an percentage juveniles in the wintering population was estimated at 12.1 % and the mean adult mortality rate was estimated at 23.6 % per year (balance-11.5%). In 1977-85, when numbers were increasing by 4.6 % per annum, the average juvenile percentage was