Stieition of IL-lix ncmorali>5 by the Sonrj-Thrugh. 



IjIV. — The defection of Helix noinoralis hi/ the Sow/ -Thrush 

 (Tardus luusicus). By Maud D. II.vviland, lion. Mem. 

 B.O.U,, and Fraxcks Pitt. 



Section I. liy Maiu I). Haviland. 



Ax artirlc on " ShoU-baiiding as a Means of Protection," by 

 A. E. Truenian, appeared in the Ann. & Maj^. Nat. Hist., 

 October 191 H, and is of considerable interest, for it deals 

 with thestrikinpj haliit of the song-thrush (Titrfius musicux) 

 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. Truenian '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. Helix 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 aljundant on the open spaces among tlie 

 short herbage, while the heavily banded specimens predomi- 

 nated in the buslies. If a collection liad 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 incons|)icuon8 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 hands of black and yellow will be clearly defined. 



