POMATORHINE SKUA. 261 



Pomatorhine Skua. Sfercorarius pomarvms (Temm.). 



The Pomatorhine, Pomarine, or Twist-tailed Skua (Plate 115) 

 is another skua with an Arctic circumpolar range and a south- 

 ward pelagic migration in autumn. It visits our shores in 

 autumn, sometimes in spring, and young birds have been 

 observed in summer ; as a winter visitor it occurs at sea near the 

 south coast. In the so-called skua-years many hundreds have 

 been driven shoreward, and not a few picked up inland. The 

 most noticeable of these invasions were in the autumns of 

 1879-1881, and were very marked upon the Yorkshire coast. 

 Though looked upon as irregular in its visits, it appears that this 

 and other species migrate normally at some distance from the 

 land ; adverse conditions explain their appearance on the shore. 



The Pomatorhine is intermediate in size between the Great and 

 Arctic Skua, and, though it occasionally exhibits dimorphism, is 

 usually of the same brown and whitish pattern as the Long- 

 tailed and light phase of the Arctic. The tail of the mature 

 bird differs from that of all others, for not only are the two 

 central feathers rounded at their tips, but they are twisted so 

 that they are at an angle, sometimes almost a right angle, to the 

 outer feathers. The effect is curious, and when in its chases 

 the bird hovers over its dodging victim, the tail is expanded or 

 closed like a fan. When open it looks square, the twist of the 

 shafts of the streamers giving them a paddled-shaped appearance 

 as they project beyond the fanned-out outer feathers. I have only 

 twice seen the mature bird on the wing, but the rounded paddles 

 caught my eye at once. Barrington believed that the tips of 

 the tail were broken off by rough winds, weakened by the twist 

 in the shaft, as he came across many specimens thus mutilated ; 

 he thought that this was more likely than that they had been 

 nipped off by other birds. In young birds the central feathers 

 are but little elongated. The flight is hardly so free and 

 rollicking as that of the Arctic, nor so graceful as Buffon's, but 



