530 Selection of Helix nemoralis by the Song-Thrush. 
inherited is the 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 considerable 
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—formulz 00000, 12345, and 
(12345). The results, which are summarized in Table IV., 
seem to show that the snails were selected quite at random, 
so that any preponderance of unbahded 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 ” found 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 chiefly by the proportions present in the 
locality. 
TaBxe IV, 
Helix nemoralis offered to and eaten by Thrush. 
Formula. Offered. Eaten. Per cent. 
00000 «0% «05% sa clenee 56 26 46-4 
P2G4D: s,s wate wie -q are 49 21 42°8 
(12885). ees 39 23 56-4 
TaBLe V, 
“ Anvil” Collection from Bridgenorth, Shropshire. 
Formula. Number. Per cent. 
OOO00 3. ats reels eaaetammmisiets «see 5 bere 
PQS4S $i, he Wisk LSA eeee ne 24 13 28'8 
12845) ui: bbe Se ae 1 22 
L2G(AD) tes hao wD alolays ySEIE Newel hey 4 88 
TEC E Ss) ea ee ee tra Sve 1 2-2 
(12) (BES ek ec ieee ee. 1 2-2 
(123)(45)! SIS, Ne. he ace ae eos 7 155 
KAZS AD) hs ACF ALE (ie hor one eae 10 22°2 
