226 SEA-BIRDS 



probably strongest at that age (Williamson, 1 949) ; but it gradually 

 weakens, until, at the end of the fledging-period, the adults have lost 

 all interest in defending their young in any manner at all. Williamson 

 found that the arctic skua was fledged in 27-33 days, the period varying 

 probably with the abundance or otherwise of the fish-food pirated from 

 the kittiwakes. 



The adults do not accompany the young skuas at sea (Perry, 1948), 

 which gradually learn to feed for themselves, hawking over the sea 

 after kittiwakes, gulls and terns; they will chase small birds indus- 

 triously, if seldom successfully at first. The flocks of young skuas at 

 British breeding grounds thin out by mid-August as one by one 

 individuals take to the open sea. The adults have gone ahead, likewise 

 singly or in very small parties. For the most part skuas are solitary 

 at sea; but where gulls and terns concentrate to feed on shoals of 

 fish, a number of skuas will gather with intent to plunder the fishers. 



The immature birds do not hurry north in the spring. We have 

 seen numbers off the south coast of Portugal at midsummer. They 

 may not reach the breeding ground until they are in their third 

 summer. They will then take part in those social activities seen in 

 individual non-breeding sea-birds of other species, previously described, 

 including communal bathing in fresh water (a favourite habit of skuas), 

 and incomplete courtship displays; and so they familiarise themselves 

 with the future nesting region. 



The departure of the adults may be hastened in August by the 

 early autumnal moult which takes place at sea. In spring there is 

 another moult, into the richer coloured summer body plumage in 

 which the adults arrive at the breeding grounds. The wing-coverts, 

 quills and tail are apparently moulted only once a year, gradually 

 during the winter, so that the skua is never much incapacitated in 

 his piratical profession by this annual process. 



