206 THE SKUAS 



britanniciis, to the extent that the light form of Arctic-skua differs 

 from the dark, they would generally be classed as distinct species. 

 Whether the variation in the Arctic and Pomatorhine-skuas is to be 

 regarded as the result of the interbreeding of two allied forms 

 inhabiting the same geographical area, or whether it results from 

 some other cause, are questions that it would scarcely be profitable 

 to discuss till we are in possession of more detailed information. 



The great-skua arrives at its breeding-place about the beginning 

 of April, 1 therefore earlier than the Arctic, which does not appear 

 till towards the end of the same month. The breeding-grounds 

 of the two species may be near together, as on Herma Ness, in the 

 island of Unst (Shetlands). Both like open ground, rough waste, or 

 moorland. The great-skua prefers high ground, and, in the British 

 Isles, the same may be said of the Arctic, which breeds, however, 

 further inland than the larger species, hummock-covered open moor- 

 land being its favourite haunt. In Norway, according to Collett, it 

 is found usually on hummocky vegetation-covered flats near water, 

 and only exceptionally far inland. 2 



Little has been recorded of their displays or gestures, and this 

 little we owe to Mr. E. Selous. Of the larger species he writes : 

 " Often when one of the great-skuas is circling round, and the other 

 standing at its post, this one will stretch itself up and raise its wings 

 above the back every time its partner passes. This raising of the 

 wings enters into one of the most salient of the many nuptial antics 

 of this bird, which I will now describe. In its completest form it 

 commences aerially. Two birds have been circle-soaring one above 

 the other, and are now at a considerable height above one of their 

 chosen standing-places, when the lower one floats with the wings 

 extended, but raised very considerably half way, perhaps, towards 

 meeting over the back an action which in their flight is uncommon. 

 As it does this it utters a note like a-er, a-er, a-er (a as in ' as '), upon 



1 Definite dates for its arrival at Foula are March 27 to April 3, 1891 ; first week April 1893, 

 recorded by Mr. Eagle Clarke in the Annals of Scottish Natural History, 1892-4. 

 1 Naumann, Vogel Mitteleuropas, xi. 327. 



