Breeding success and chick growth of red-throated divers Gavia stellata in Shetland 1979-88

Okill, JD.; Wanless, S.

During a ten year study there was considerable year to year variation in the number of Red-throated Diver pairs found breeding successfully each July. The proportion of pairs with broods of two chicks also varied annually, tending to be higher in years when many successful pairs were found and lower when fewer pairs were located. Over a nine year period the frequency with which lochs of less than 0.3 ha were occupied by successful pairs was more than twice that of larger lochs. Generalized growth curves of weight, bull and tarsus length in relation to wing length were determined for more than 600 chicks. Predicted annual weights for chicks with a wing length of 180 mm were significantly lower for b-chicks than either single chicks or a-chick, but were not correlated with an index of breeding success.