Rooks (Corvus frugilegus) dine on snails in Poland

Evidence of breeding rooks feeding on Roman snails (Helix pomatia) and grove snails (Cepaea nemoralis) is presented. Shell dimensions of food remains and intact Roman snails collected in the study area were measured in order to estimate the size and shape of the snails collected by rooks in relation to the food available in the vicinity of the rookery. Smaller and rounder snail shells were collected by rooks than were available in the area around the colony, indicating that the rooks collected most of the snails elsewhere, in forests, gardens, or ruderal areas located near the colony. A general preference for prey items was ca. 12 cm3 or 19 g shell size. Moreover, rooks collected yellow grove snail shells and shells with stripes. In addition, snails with a more contrasting layout of shell stripes were collected more often than plain snails.