Incubation and brooding rhythm of the Cape Petrel Daption capense at Nelson Island, South Shetland Islands, Antarctica

Incubation and brooding performance of the Cape Petrel Daption capense at Nelson Island, South Shetland Islands, Antarctica, in the 1991 -1992 austral summer is reported in detail and compared with data from two other areas. There was an inverse relationship between the mean foraging trip length and mean peak weight of chicks. Variation in shift length throughout incubation resulted from a combination of seasonal effects (food supply) and behavioural adjustment to hatching. The length of the last incubation shift was independent of its number but decreased with date of initiation. The average weight of nestattending birds increased steadily during the incubation period and at the same rate in both sexes. Females attained seasonal peak body-weight before the egg hatched, whereas males just recovered their pre-breeding weight. Males took on a slightly larger share of incubation (52%, range 40–63%) and invested more time in mutual nest attendance. Length of foraging trips varied consistently in pairs and individuals, its repeatability being twice as high in females as in males. The incubation performance of individual females (length of the first and an average foraging trip) was correlated with the size of the egg they had laid and also to subsequent chick growth and fledging success. There was a tendency in successful pairs to spend more time together at the nest and to have shorter foraging trips. I suggest that variation in breeding performance among pairs was mainly a result of individual variation in female quality, with pairs where the female contributed more to incubation being more successful. There is little evidence that egg losses were caused by parental errors.