60 THE ZOOLOGIST. 



from a foot to twelve yards. One furrow that I measured was 

 exactly twelve yards long, and had occupied its maker for at 

 least three hours, and possibly twice this time. Now, allowing 

 the width of the disturbed sand to be six inches (really this is the 

 distance between the summits of the ridges thrown up on each 

 side of the furrow), and the number of crustaceans twenty 

 to the square inch, we find the total weight to be about a 

 pound and a half. The greater part of this would go down 

 the throat of the bird, for I do not think that many of the 

 crustaceans are allowed to escape once they are driven from 

 their burrows. 



As the pools diminish in size these curious markings are left 

 on the bare sand, sometimes in great numbers where the Gulls 

 have been congregated. I do not know if anyone has ever 

 noticed these very conspicuous furrows, but I should expect them 

 to present rather a stiff problem for an enquiring mind who did 

 not think of the agency of birds. I ought to add here that I 

 have often observed this very extraordinary dancing habit of 

 Gulls on other estuaries, but I think it safest to say that I have 

 no note of the actual species, nor of the food sought. Possibly 

 the Black-headed Gull may prove to be the only species addicted 

 to the habit, for I have seen it so employed while in the imme- 

 diate company of other Gulls that stood by and looked rather 

 hard-up for a meal. On the estuaries of the Conway and of the 

 Clwyd I have sat and watched the Gulls dancing in the mud on 

 very many occasions. 



In the summer of 1912 a tiny sandy bay on the north coast 

 of Yorkshire was swarming with Sandhoppers (Talitrus locusta)* 

 and each evening a flock of a hundred Black-headed Gulls, 

 accompanied by either two or three immature Kittiwakes, 

 patrolled the sands, snapping up these agile crustaceans. Each 

 bird marched steadfastly forwards, and picked at any hopper 

 that happened to be in the air within a couple of inches of its beak 

 at the moment the bird had disposed of the last one captured. The 

 resulting gait was indescribably ludicrous to watch, for it re- 

 sembled a violent form of palsy as the accompaniment of a 



* Possibly this is the species that crammed the stomach of a Cuckoo 

 (C.canorus) shot by Dr. Stejneger on the coast of Kamtschatka. He called 

 them " the Gammaridce which abound on sandy beaches." 



