Ravens as small mammal bone accumulators: First taphonomic study on mammal remains in raven pellets

Abstract

The raven Corvus corax is one of the most common and widely distributed bird species in the northern hemisphere. Both predator and scavenger, its diet often comprises small mammals, whose bones and teeth are ejected through pellets after digestion. These pellets are frequently accumulated around the nest or roost sites, which can be used for years, even centuries. Until now, numerous studies have stressed the role of raptor pellet and mammalian scat accumulations as a source for small vertebrate palaeontological or archaeo(zoo)logical terrestrial assemblages. However, the raven, known from the Late Pliocene, has not yet been studied as a taphonomic agent. We present the first study on small mammal bone modifications from 567 raven pellets collected in Białowieża Primeval Forest (E Poland). A total of 1008 skull elements (teeth and jaws) and 812 main postcranial bones (long bones, girdles, talus, calcaneus), mainly belonging to rodents and shrews, were recovered from 129 pellets. The distinction of taphonomic features among the 5 main groups of prey (squirrels, large rodents, small rodents, shrews and moles) revealed a better representation and completeness of remains from the smallest species, and a variability in the proportion of digested teeth among different groups of prey. The global taphonomic signature of the small mammal bone assemblage appeared close to that of owls, but it placed the raven in an intermediate category of predators (between owl categories 1 to 3), according to the classification by Andrews (1990) [Andrews, P.J., 1990. Owls, caves and fossils, Natural History Museum Publications, London.]. Mineral remains from other vertebrate species (ungulates, lagomorphs, bats, birds, fish) were also frequently represented by small bone splinters (usually less than 2 cm long), egg fragments and complete elements (teeth, bones, hooves). Vegetal material, including seeds, was also frequent. The presence of such remains may be useful to distinguish a fossil bone assemblage made by raven from one originated from an owl prey accumulation. This study provides new insight to explain some small bone accumulations through Plio–Pleistocene and recent periods, particularly in mountain and cold areas. Due to its opportunistic exploitation of a wide variety of food sources, the raven may provide a more complete image of the fauna in the surrounding area of deposition than owl or small carnivore prey assemblages. Ravens associate often with open landscapes, large carnivores and human activities, a fact that might be also relevant for archaeological or archaeozoological considerations.