NEST MAINTENANCE AND STONE THEFT IN THE CHINSTRAP PENGUIN (PYGOSCELIS-ANTARCTICA) .1. SEX-ROLES AND EFFECTS ON FITNESS

Chinstrap penguins, Pygoscelis antarctica, after being relieved from i ncubation, collect stones from the ground or steal them from other nes ts and incorporate them into their own nests. The variation in stone-c ollecting behaviour after incubation reliefs, nest defence intensity a nd nest weights were measured in a sample of 100 nests in a large subc olony sited in the Vapour Col Chinstrap penguin colony on Deception Is land, South Shetland Islands. Males collected more and larger stones, stole more stones and were more aggressive in nest defence towards pot ential thieves than females. Females suffered stone theft to a greater degree than males. Nests changed in weight during a period of 20 days . Initial nest size was negatively correlated with change in nest weig ht. The intensity of stone collection and theft by males was positivel y correlated with the increase in nest weight and with the final nest weight attained, while nest defence intensity by males and females was positively correlated with initial and final nest weight. Flooding af ter a snow storm affected 31% of nests and caused the loss of up to 14 % of eggs/hatchlings. Flooded nests were significantly smaller than no n-flooded nests. Results indicate that nest maintenance behaviour and stone theft in Chinstrap penguins serve to improve nest quality and th us enhance reproductive success.