The relationship between skuas and adelie penguins at the Cape Bird colonies: penguin egg and chick mortality from skua predation and territorial, feeding and breeding behaviour of skuas about the penguin colony

A five year study on the relationship between skuas (Catharaeta maccormicki) and adelie penguins (Pygoscelis adeliae) was investigated at Cape Bird with two studies:
a) A study of penguin egg and chick mortality with reference to that attributable to skua predation and b) a study of territorial, feeding and breeding behaviour of skuas about the penguin colony with emphasis on discovering differences between pairs defending territories containing nesting penguins and pairs without penguins. The penguin colonies were mapped and divided into blocks which were numbered. Counts of nesting birds, eggs and chicks were made at weekly intervals until the creche stage.

In one year, counts were made of colonies under three conditions;
(a) colonies in which individual birds were not marked (the total number of eggs and chicks is known for each week and the average egg laying and chick hatching dates can be determined),
(b) colonies in which the nests were numbered (in these the hatching dates, age of chicks and their approximate weights when lost is known) and
(c) three colonies or parts of colonies were screened from skua predation by a wire mesh and treated as for (b).

The colonies in categories (b) and (c) were examined from outside the colony perimeter and those in (a) were disturbed when counts were made. The differences between groups (a) and (b) may demonstrate the effect of disturbance by man and those between groups (b) and (c) the effect of skua predation and conversely the mortality attributable solely to penguin mismanagement. Skua nests were mapped and birds were ringed for identification. The defence of the territory, the feeding cycle during the season and the number and duration of foraging flights over the penguin colony (and the number of attacks and successes) was recorded. The food taken by breeding skuas was investigated by regular observations on two groups of breeding skuas at the colony. Details noted included whether the eggs or chicks taken were dead or alive when taken, how they were taken and the effort required (providing a reference for assessment of each skua as a predator or scavenger). The dates during which skua were feeding at sea were found by direct observation and inference. All penguin chicks taken by skuas in Blocks F and H were weighed and their foot length were measured (later used growth of plumage feathers on the body). These two blocks were representative of areas with light and heavy skua predation respectively. In conjunction with this work, chicks within the colonies of these two areas were similarly measured. To compliment this study, examination of the behaviour of the penguin in relation to the skua and the difference in behaviour of skuas nesting at the rookeries and away from the rookeries was also investigated.