8 



THE ZOOLOGIST. 



do not apply to the sheila on the mud, which scarcely vary more 

 than from an eighth to a sixth of an inch in length. These 

 mud shells afford a possible explanation. Close inspection shows 

 that they rest upright on the mud, that large numbers of them 

 are empty, and that many others are in an unhealthy condition. 

 The gentle flow of the tide is insufficient to disturb their balance, 

 and the general appearance of all is the same. If we watch 

 quietly we may see a shell here and there move slightly, rest 

 for a while, and move slightly again. It is the same with the 

 shells on the wet sand and the rocks. In this, as I venture to 

 think, we have an explanation of the Dunlin's feverish display of 

 energy and apparent delicacy of taste. It overruns the ground 

 watching for the slightest movements made by the molluscs from 

 time to time. In this way it guards itself against shells which 

 are empty and shells whose occupants are dead or dying. Some 

 other waders do the same thing in a different way, but the 

 only way open to the Dunlin is to run ceaselessly hither and 

 thither. 



In similar fashion the Dunlin treats areas of mud crowded 

 with the open burrows of worms and thin-skinned Crustacea, 

 providing a sufficient number of the occupants are near to the 

 surface. It is, however, more circumspect in its movements, it 

 runs more slowly, and at the last moment, when on the point of 

 making a capture, it rushes forward or to one side and plunges its 

 bill quickly into the mud in an attempt to seize one of the lurking 

 animals on which it feeds. 



Search by touch alone is to some extent a misnomer. A 

 certain amount of visual information is necessary to begin with, 

 and it is a valuable adjunct during the process of tapping. The 

 Dunlin proceeds slowly a step or two at a time in no particular 

 direction, and drives its bill rapidly up and down in and out of 

 the ground, testing it very completely in front and on both sides. 

 From time to time it runs or flies to a fresh place and begins 

 again, but there is no evidence to show that the new place 

 is chosen for any special reason. In the course of the up and 

 down movement the bill shows a noticeable tremor.* At times 

 this tremor is more marked, and is seen to be vertical. To close 

 inspection it reveals itself as a lesser up and down movement 



* Macgillivray, ' History of British Birds,' iv. pp. 207-213. 



