171 



THRUSH STONES AND HELIX 

 NEMORALIS L. 



E. ADRIAN WOODRUFFE-PEACOCK, F.L.S., F.G.S. 



Thrush stones have interested me from my childhood onward, 

 and I have collected tens of thousands of broken shells from 

 them at various times. Sometimes thousands of shells may be 

 found at a single anvil, on peat, fresh-water or estuarine 

 alluvium, for stones or bricks are rare on such soils. They 

 have always to be carried to the spots where the birds find them 

 by man. When they are most pressed for animal food in 

 severe winters or dry springs, the thrushes are not backward 

 in finding fair substitutes for hard stones for anvils. The becks 

 of the incline towards the great fenland, and of our smaller 

 valleys, freeze, thaw^ partly, break up into floes, jam, and freeze 

 again, presenting irregularities of surface, which the birds are 

 quick enough to turn to good use. A stone standing slightly 

 above the road or footpath level, the lowest bars of gates, the 

 sharp points of low-set barbed-wire, or even ' the stubs ' in a 

 laid fence are not forgotten when other means fail them. 



The whole subject is interesting, but does not give any 

 approximate scientific results, until a fairly simple and ready 

 field-method of recording the relationship of the banding to 

 the interspacing on the shells is brought into use. When an 

 elastic formula is found, the nexus between the shells of a given 

 spot, their environment, and the thrushes is partly disclosed, 

 and becomes explicable. Any method of recording to be of 

 true use must be sufficiently simple to be applied, not only to 

 specimens in collections, but at once in the field to the living 

 molluscs. If it is too complicated, the relationship between the 

 supply of shells on a given spot and those that are badly pro- 

 tected for want of banding, or by limited banding, and so are 

 easily discovered by the birds, cannot be worked out. 



When a long series of H. nemoralis is brought together from 

 one place and is examined critically, it will be discovered that 

 there is a common relationship and law of banding and inter- 

 spacing prevalent among these local specimens. It has also a 

 distinct relationship to their former environment. For in- 

 stance, the form 12045 of the old notation, may be met with 

 for 200 yards on one side of a stream and then be absent for 

 miles, till it is picked up again, and is discovered to have a 



1909 May 



