THE GREAT AND ARCTIC-SKUAS 213 



first by the gull that catches and then by the great-skua that robs. 

 If it be granted that they are swallowed head first, it is quite con- 

 ceivable that the head is sufficiently loosened by the softening process 

 of the crop or of the proventriculus to become detached from the body 

 under the strain of the second regurgitation. What lends support to 

 this view is that, in the case of gannets, I have noted that the fish 

 disgorged by the parents, if these happen to be alarmed before they 

 have had time to feed their young, have the heads partially digested. 

 Had the fish been subjected to a second process of digestion in the 

 stomach of a skua, and to a second wrench upward through the gullet, 

 it seems reasonable to suppose that they would have left then* heads 

 behind them. I may add that I have seen a young gannet disgorge a 

 fish head-first, a fact which shows that it took it from the parent's 

 throat tail-first, and that the parent swallowed it head-first 



The fish found lying whole may simply not have been digested 

 long enough to lose their heads, and may have been taken from Terns, 

 which carry their capture in the beak. 



This does not, however, explain either why so many fish are found 

 lying about unswallowed, or why the same fact has not been observed 

 in the case of the Arctic-skua. BufFon's skua heaps up dead lemmings 

 beside its nest, seemingly as a store to be drawn upon (p. 227). In 

 circumpolar breeding-grounds, where supplies are less assured than 

 farther south (pp. 225-6), such a provision may be necessary. The 

 same necessity may formerly have operated in the case of the great- 

 skua, its present habit of leaving fish about being of the nature of a 

 survival. 



The chief victims of the piratical exploits of the Arctic-skua are 

 the smaller Gulls and the Arctic-tern, especially the latter, no doubt 

 on account of its habit of carrying its catch in the bill, an appetising 

 morsel for all to see. Guillemots, puffins, and the larger Gulls are 

 also pursued. Saxby states that fish are taken even from the great 

 blackbacked-gull, but this must be exceptional When an Arctic- 

 skua has singled out a victim to be robbed, it chases it with light- 



