OWL PREDATION ON 2 SYMPATRIC SPECIES OF TUCO-TUCOS (RODENTIA, OCTODONTIDAE)

Predation by owls upon two sympatric species of subterranean rodents t he genus Ctenomys was studied by comparing characteristics of individu als that were field-trapped and preyed upon. Predators took a greater proportion of the smaller C talarum than of the larger C australis in comparison to that estimated from their respective field densities. On ly subadult individuals of C australis were found among pellets. For C . talarum, a greater proportion of subadults than of adults was observ ed in pellets. We suggest that this pattern is determined both by cons traints imposed by size of prey on the ability of a predator to handle large prey and by greater exposure of dispersing subadults to predati on. Differential predation possibly maintains the habitat segregation observed between C talarum and C australis.