‘Selection of Helix nemoralis by the Song-Thrush. 525 
LIV.—The Selection of Helix nemoralis by the Song-Thrush 
(Turdus musicus). By Mavup D. Havitanp, Hon. Mem. 
B.0.U., and Frances Pirt. 
Section I. By Maun D. Havinanp. 
Aw article on “‘ Shell-banding as a Means of Protection,” by 
A. E. Trueman, appeared in the Ann. & Mag. Nat. Hist., 
October 1916, and is of considerable interest, for it deals 
with the striking habit of the song-thrush (Turdus musicus) 
to break small shells habitually upon certain stones or 
“anvils,” and this habit is rare among birds. At first 
sight, the author’s conclusions seem to give proof of natural 
selection in operation; but when the matter is examined 
more closely, it is not so clear, and some of Mr. Trueman’s 
methods invite criticism. 
It would have been well if he had given a detailed account 
of the wide area in which his ‘‘ anvil” and “ control” collec- 
tions were made. The area is described only as a belt of 
country on the Magnesian Limestone, some 3 miles long, 
between certain named localities. Helia nemoralis varies 
almost from one ditch to another, as, indeed, is exemplified 
in Mr. Trueman’s paper, and, unless the control collections 
were made immediately round their respective anvils, they 
may be very misleading. In a collection made at Quy Fen, 
Cambridgeshire—a piece of marshy pasture-land interspersed 
with clumps of willow and bramble-bushes,—it was found, 
although exact figures were not kept, that lightly banded 
snails were more abundant on the open spaces among the 
short herbage, while the heavily banded specimens predomi- 
nated in the bushes. If a collection had been made, for 
instance, only in the open, it would not have been really 
representative of the snails in the locality in general. 
Another weak spot in Mr. Trueman’s control collection is 
that it was formed of dead shells. How can one be sure 
that the shells were in the same situations and positions as 
when they were alive? It is much to be doubted whether 
protective devices are of much avail to any creatures that 
are preyed upon by ground-feeding birds. Striped coloration 
is inconspicuous only when viewed from a distance ; the. 
pied striping on the snout of the badger or on the neck of 
the black-throated diver are cases in point. But when a 
bird sees a snail among herbage at a distance of only a few 
inches the bands of black and yellow will be clearly defined. 
