A STUDY OF A CRUSTACEAN. 61 



preternaturally grave and decorous walk. Thus the whole flock 

 marched on, each head bobbing with clock-like regularity, and 

 in apparent ahnlessness ; but probably most of the snatches 

 were successful, although of course we were too far distant to 

 detect the actual insects. When it was too dark to read we could 

 still see the Gulls working as freely as ever, and could not but 

 admire the perfection of eye and beak that made this business 

 possible. 



On our Westmorland estuary we found the young birds of 

 the year, fresh no doubt from the great Eavenglass gullery, as 

 assiduous as their elders in the remunerative dance. At night, 

 when it was too dark to see them, we could plainly hear the 

 measured splashing from the tireless birds ; and in what way 

 are we to understand how they were enabled to see the crusta- 

 ceans through a couple of inches of disturbed water ? Bad 

 enough in the daytime, it is either worse at night or — the Gull 

 has a sense of sight of a quality unknown to us, and with 

 powers that merit a position as a sixth sense. There are many 

 published records of the Black-headed Gull catching insects in 

 flight, and it has been observed that regular aerial feeding 

 excursions are made after dark.* 



The fauna of the more or less permanent tide-pools was too 

 complicated for exact observations, but the shallower pools could 

 be surveyed with great convenience, and I was able to convince 

 myself that, exclusive of microscopical organisms, they were 

 inhabited only by Corophium. Gulls, therefore, which were seen 

 at these places could be feeding only on this crustacean, and on 

 nothing else. 



I would like again to draw attention to the fact that birds of 

 the year were using this curious " dancing " method of obtaining 

 food in July. Is it instinctive ? If not, and if they were merely 

 following the example of their elders, why did not the Kittiwakes 

 off Grange copy their companions ? Do other birds, in other 

 localities, feed on Coropliium or similar sand or mud inhabitants 

 in a similar manner? Do the Gulls tread out other inverte- 



* Perhaps here I can repeat a note (c/. ' Naturalist,' 1908, p. 456) of my 

 own on a Buffon's Skua, the stomach of which contained the remains of 

 Craneflies and a species of Syrphid, the last recognized by the characteristic 

 "false-vein" of the wings. 



