THE POMATORHINE-SKUA 219 



the ravenous skuas. Possibly, as suggested by Mr. Stevenson, the 

 enormous shoals of herrings and sprats which frequented the North 

 Sea in the autumn of 1879 induced the gulls and skuas to linger on 

 their way south, on account of the abundant supply of food, until the 

 gales of October drove them helplessly on to the coasts of Yorkshire 

 and East Anglia. 



To distinguish an adult pomatorhine-skua in perfect plumage on 

 migration is a comparatively simple task. It is a much smaller and 

 lighter-looking bird than the great-skua, and at the same time is 

 larger than either Richardson's or Buffon's skua. Its flight is not 

 so heavy as that of the great-skua, but is somewhat Tern-like 

 and angular, and it is less active than the two smaller species. Of 

 course, the short tail of the great-skua is another useful character in 

 distinguishing it from adult birds of other species. The adult 

 pomatorhine, Buffon's, and Richardson's skuas all have the middle 

 pair of tail feathers elongated, but in the first-named species 

 they have also the extraordinary peculiarity of being twisted into 

 a plane almost at right angles to the shorter tail feathers. They 

 are also bluntly rounded at the ends instead of coming to a point, 

 as in Buffon's skua. This gives a curiously thick and clumsy 

 appearance to the tail of the bird when seen on the wing, and 

 enables one to identify it with certainty in many cases at considerable 

 distances. 



But it must not be supposed that all birds have this peculiarity 

 fully developed. E. T. Booth, who kept this species in confinement 

 for some years, and studied its changes of plumage, was of opinion 

 that the perfectly adult plumage was not assumed till the fifth year, 

 and that birds of the second or third year rarely occurred off our 

 coasts. It is not surprising that many of the birds which visit us are 

 birds of the year or immature, and in such cases the middle tail 

 feathers are only slightly elongated. During the invasion of 1879 

 Alfred Roberts noticed that they chased the smaller Buffon's skuas 

 and snipped off their long tail feathers in the scramble for food, 



VOL. III. 2 F 



