HIGH ANNUAL VARIABILITY IN REPRODUCTIVE SUCCESS OF KITTIWAKES (RISSA-TRIDACTYLA L) AT A COLONY IN WESTERN ALASKA

(1) All aspects of reproductive performance of kittiwakes (Rissa tridactyla L.) fluctuated markedly in 1975-89 at a colony of about 10 000 nesting pairs in the north-eastern Bering Sea, Alaska. (2) In breeding seasons following cold springs, breeding was delayed, fewer nests were built, fewer nests contained eggs, and clutch size, hatching success and the number of chicks fledging per nest were reduced. Complete reproductive failures followed the three coldest springs in the 15-year period. (3) Reproductive success (chicks fledged per nest) was highest following moderately warm springs; however, growth rates of chicks and fledging success were extremely low following the warmest spring on record. (4) Spring air temperatures were highly correlated with break-up of sea ice and these factors probably influenced seasonal warming trends in the sea water and the consequent availability of prey such as sandeels (Ammodytes hexapterus Pallas) near the colony. (5) During this 15-year period, interannual variability in spring air temperature was pronounced in comparison to that during the previous 68-year period; however, simulations using May temperature as a predictor of reproductive success suggested that high annual variability in reproduction has occurred throughout this century. (6) Numbers of adult-plumaged birds on the cliffs in mid-season were markedly lower and more variable in years when few nests were built, suggesting that relatively few experienced adults breed and consistently are present at the colony in years when overall reproductive performance is poor.