Broken Littorina littorea shells: predation by birds?

Littorina littorea shells found broken on a cycle-track next to where they lived, are thought to be broken by shell-dropping birds. Shells broken experimentally by dropping them from 6 m height on a concrete floor showed very similar damage: a hole in the last whorl, whereas the aperture rim remained intact. Examples from the literature indicate this shell damage to be characteristic for shell-dropping by birds. We suspect carrion crows as the culprit, but field observations have to prove this.