Owl pellets dispersal by wind: observations and experimentations

Abstract

Pellets produced and accumulated by owls are subject to biological and atmospherical agents, and may be dispersed before their disaggregation. Observations on dispersion of Athene cunicularia and Tyto alba(Aves, Strigiformes) pellets were performed in a natural environment (Pampean region, Argentina) and in a wind tunnel. Ten burrows were visited, and the distances of pellets and isolated bones from the burrow entrance holes were registered. Intact pellets predominated between 0 and 1 m from the entrance holes. Partially disaggregated and disaggregated pellets showed similar distributions. In two burrows, the transport of new pellets and incorporated bones was observed during one month. Only in a few cases were the pellets mobilized and reoriented according to the predominant winds. Substratefeatures or the presence of vegetation favored fixing of their positions and prevented their mobility. Many of the pellets suffered total disaggregation or burial within the first 20 days to 1 month. Evaluated isolated bones showed a greater representation of mandibles and long bones, as well as skeletal elementswith low susceptibility to wind transport. Pellets evaluated in the wind tunnel, at low wind speed (2.70 m/s), were mobilized very short distances. At high wind speed (4.70 m/s), transport distance was greater. The distances travelled could be related to their initial orientation at the beginning of the experiments, as those that were placed at 90 to the wind flow showed greater transport. Theobservations showed that there were some differences in mobility between pellets of A. cunicularia and T. alba, as A. cunicularia were more susceptible to transport at each wind speed, likely attributed to their smaller size. Wind increased bone dispersion from partially disaggregated pellets, causing the loss of some of them.