42 BRITISH SEA BIRDS 



a terror to the Gulls and Terns ; merciless robbers 

 of the hard-won spoil of more weakly species ; 

 destroyers even of the eggs and helpless young of 

 other sea birds. All the four species of northern 

 Skuas are visitors to the British Seas, but only two 

 of them are indigenous to our islands. The first 

 of these to be noticed here is the Great Skua, 

 Stercorarius catarrhactes, one of the most local of 

 British birds during the breeding season, as its only 

 known nesting places in our area are on Unst 

 and Foula, two small islands of the Shetland 

 Group. Except during the breeding season, the 

 Great Skua is mostly oceanic in its habitat, 

 wandering long distances from land in quest of 

 prey, attending vessels and fishing fleets, only 

 drawing landwards by stress of weather or un- 

 usual abundance of food. This Skua is practically 

 omnivorous. During its summer sojourn near and 

 on the land it repeatedly raids the colonies of other 

 sea fowl, to prey upon exposed eggs or unguarded 

 young ; it captures the smaller Gulls, notably the 

 Kittiwake : it also picks up any stranded fish or 

 other carrion ; and is constantly on the watch to 

 chase any Gull or Tern that catches a fish, 

 following the poor bird with fatal persistency 

 until, terror stricken, it disgorges its food, which is 

 promptly seized by the voracious Skua. The call 

 note of this Skua is very similar to that of the 

 Lesser Black-backed Gull, but when under the 

 excitement of chasing other birds, or of seeking 



