An ecological study of crocodiles in Ruhuna national park, Sri Lanka (with three text-figures)

Abstract

A study was carried out in Block I (140 sq. km) of the Ruhuna National Park (RNP) opportunistically from October 1991' to October 1994, in order to study the two species of crocodiles occurring in Sri Lanka, viz. Crocodylus palustris and C. porosus. A total of 341 sightings of the two species were made on 77 occasions, 307 sightings on C. palustris and 34 sightings on C. porosus. Among C. palustris, solitary animals made up most of the observations (55.8%) while pairs accounted for 13.0%. Of the 22 water-holes that were surveyed, 13 (59%) had only one crocodile. Although both species could be seen at any time of the day, the number basking increased with the increase in the ambient temperature, and peaked around noon. C. porosus basked alone, and C. palustris communally. The population structure consisted of 44% hatchlings, 6%juveniles, 24% subadults and 26% adults. Only adults of C. porosus were observed. Hatchling losses can be very high through predation by birds and mammals. Both species feed on a variety of food, ranging in size from aquatic insects and Crustacea (in hatchlings) to fish, frogs, birds and large mammals (in adults). The minimum crude density values for C. palustris and C. porosus are estimated to be 0.72 and 0.07 animals per sq. km respectively. The populations of both species in Block I appear to be secure and viable.