BIRDS TAKING RUBBER ARTICLES. 29
Lister and J. Seabrooke, the former second-hand, the rubber was
found in the pellets, but on the other hand P. Thompson and
Miss A. Hibbert-Ware call attention to the fact that the rubber
articles referred to by them were not found in the pellets, and
they had no evidence to suggest that they ever had been. It
is suitable to interpolate at this point that in the case of the
Rook the habit was recorded from three widely separated
localities, and that at one of these it had persisted for twenty
years ; it is almost certain that the same individuals and their
descendants were implicated. On prima facie evidence it would
appear that colour does not influence the habit, judging by the
various colours of the objects taken, but to come to a definite
conclusion it would be necessary to know what colours had been
available in each locality. Even if we allow that other instances
have been recorded beyond those mentioned, the taking of rubber
by birds must be considered as being very unusual. I have
searched a number of works dealing with the food of birds,
including The Food of some British Wild Birds, by R. Newstead,
and The Food of some British Wild Birds, by W. E. Collinge, but
cannot find any reference to rubber having been found in the
food-contents. I am further informed by the latter in a letter
dated November 18th, 1937, that during his numerous post-
mortems he had never found any rubber material of any kind nor
had he noticed among doubtful matter (of which the percentage
was extremely small) anything which resembled rubber. In
considering why these objects are taken we have great difficulty
in accepting the suggestion that the birds mistake them for
edible matter, but Mr. Rooke's idea that they might be picked
up with natural food seems quite feasible. Our view is that the
objects are swallowed as an aid to digestion or to act as an emetic
in the rejection of the indigestible matter eaten.
REFERENCES.
1890. The Birds of Essex. Miller Christy, p. 135.
1909. Pellets Cast up by Rooks. Miss G. Lister, Miller Christy,
Jonathan Seabrooke. Essex Naturalist, v., xvi., pp. 119-21.
1922 Bird Pellets and their Evidence as to the Food of Birds. P.
Thompson, op, cit., v., xx., p. 125.
1930 Rooks Collecting Rubber Objects. Miss A. Hibbert-Ware.
British Birds, v., xxiv., p. 27.
1937. Birds Taking Rubber Rings. British Birds, G. C. S. Ingram and
H. M. Salmon, v., xxx., p. 374 ; K. B. Rooke, v., xxxi., p. 64.