Actualistic taphonomy of microvertebrates ingested by the barn owl (Tyto alba) in a forested area. Implications for the fossil record

Abstract

Rodents are common prey of nocturnal raptor birds, which ingest whole individuals and subsequently expel partially digested remains as regurgitated pellets. This generates accumulations of skeletal elements that may become part of the fossil record. Inferring which predator was responsible of any given fossil microvertebrate assemblage allows assessing potential biases and making paleoecological inferences. Neotaphonomic studies allow modelling the particularities characterizing different raptors under different environmental conditions. Based on them, it is possible to suggest the predator involved in fossil microvertebrate assemblages by considering the taxonomic and anatomical abundance, the degree of digestive corrosion and that of breakage of skeletal remains. Yet, no detailed neotaphonomic studies on raptors had been made so far in NW Argentina, and other studies in South America have been made mainly in open and arid environments. This has forced paleontological studies to use analogues that might not be fully relevant. Here we present an actualistic study on rodent skeletal remains (NISP = 7540) recovered from modern pellets produced by the barn owl (Tyto alba), recovered at Villa Padre Monti (Tucumán, Argentina), a Yungas forest area partially affected by the presence of crops. The aim is to characterize the taphonomic traces of T. alba under these environmental conditions. The assemblage is composed of at least five species of Cricetidae rodents and a varied representation of skeletal elements, especially of the post-cranium; it has a high relative anatomical abundance (58.7%). Skeletal breakage levels are low, especially in the mandibles and post-cranium. Digestive corrosion is predominantly absent (62.1%) to light, although some elements with high degrees of digestive corrosion were found, even in the extreme digestion category. These results generally compare well with other taphonomic studies on the barn owl, and add data to the known variability of modern accumulations by this Strigiformes. They are thus expected to have an impact on the interpretations of fossil faunas.