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Thrush Predation on the Snail Cepaea hortensis
C. B. Goodhart
Journal of Animal Ecology
Vol. 27, No. 1 (May, 1958), pp. 47-57
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2173
Page Count: 11
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1. Shells of Cepaea hortensis eaten by song thrushes were collected from the same area every month for three years. 2. The birds fed on snails only during two restricted periods of the year, in January, February and March, and in June and July, with hardly any taken in between C. hortensis is probably not very palatable as food to thrushes and serves as an ecological reserve, being taken only when other food is short during cold weather in the winter, and in mid-summer after the spring flush of caterpillars and before there is much fruit available. 3. During the winter feeding period quite a high proportion of dead empty shells were taken by thrushes to their anvils. 4. There was evidence of a systematic seasonal change in the anvil sites. 5. Significantly more pink than yellow shells were taken by thrushes in the summer than in the winter feeding periods, but no differential predation of the various shell banding patterns could be observed. Various possible reasons for this differential predation are discussed, and it is concluded that visual selection by birds, rather than genetic differences in activity in the snails, provides the best explanation. This could be responsible for maintaining some `predation polymorphism' in the species, but the situation is a complex one and there are certainly other factors involved as well.
Journal of Animal Ecology © 1958 British Ecological Society