Ontogenetic dietary partitioning by Crocodylus johnstoni during the dry season

We examined size-related dietary patterns in a Queensland population of the Australian freshwater crocodile (Crocodylus johnstoni). In three consecutive dry seasons, we stomach flushed crocodiles (n = 324) to record the numerical frequency and percent occurrence of prey items. Prey included spiders, aquatic insects, terrestrial insects, shrimp, fish, anurans, turtles, snakes, mammals, and birds. The diet of C. johnstoni showed ontogenetic shifts as the cranium broadened and once body size exceeded 60 cm SVL. With increasing crocodile size, the ingestion of spiders, insects, and anurans declined strongly whereas the consumption of fish, turtles, and snakes increased strongly. Shrimp were eaten at low and variable levels by all size classes of crocodile. The low overall prevalence of mammals and birds suggested that they were consumed opportunistically by the larger crocodiles. With increasing crocodile size, there were overall increases in prey richness and significant declines in realized dietary niche, dietary breadth, and mean number of prey items per crocodile. There were no significant changes in dietary diversity, evenness, or number of equally common prey species