Although ,specific to Raven Corvus corax there are three pieces of work relating to shell recovery from regurgitated pellets.
Bolam G. 1913. Wildlife in Wales. London. Frank Palmer.
Ewins et al 1986. The Distribution, Breeding and Diet of Ravens Corvus corax in Shetland. Bird Study. 33. 110-16.
Berrow S. 1992. The Diet of Coastal Breeding Ravens in County Cork. Irish Birds. 4. 555-8.
Sorry, I don't have pdf's of these. Hope this is of use though.