530 Selection of Helix nemoralis !>}/ tlie Song -Thrush. 



inherited is tlie impulse to beat living prey on some hard 

 object, although in one instance I saw the thrush hammer 

 a snail on a sofa-cushion. The habit can be perfected by 

 time and practice, and as it grew older the bird became 

 increasingly expert, for the work requires consideiable 

 effort, especially when dealing with strong mature shells. 



As regards the selection of a particular type of shell, my 

 experiments gave negative results. I never offered more 

 than three snails at one time — formulae 00000, 12345, and 

 (12345). The results, which are su;nmarized in Table IV., 

 seem to show that the snails were selected quite at random, 

 so that any preponderance of unhanded types at '' anvils^' is 

 not due to selection by thrushes. I offered specimens of 

 both castanea and rubella to the bird, and the results show 

 that, although a greater number of castanea were left 

 unbroken than of other hues, this was due to the stouter 

 shell. As it became more practised, the bird learnt to . 

 break them as readily as the more thin-shelled varieties. 



Table V. shows the contents of three '^anvils " fouml near 

 Bridgenorth in Shropshire on a roadside bank in a wooded 

 district, and Table VI. shows a control collection made in 

 the vicinity. 



From the evidence afforded by this captive thrush, and by 

 the " anvils " in this district, I conclude that the proportions 

 of varieties of Helix nemoralis found at the breaking-stones 

 is influenced chietly by the proportions present in the 

 locality. 



Table IV. 



Helix nemoralis offered to and eaten by Thrush, 



Formula. Offered. Eaten. Per cent. 



00000 56 26 46-4 



12345 49 21 428 



(12345) 39 23 56-4 



Table V. 

 "Anvil" Collection from Bridyenorth, Shropshire. 



J'ormula. Number. Per cent. 



OOOOO 5 17-7 



12345.. 13 28-8 



12(345) 1 2-2 



12.X45) 4 8-8 



1(23)(45) 1 2-2 



(12)(.34.5) 1 2-2 



(123)(45) 7 15-5 



(12345) 10 22-2 



i 



