Paleosuchus trigonatus Nests: Sources of Heat and Embryo Sex Ratios

Abstract

All crocodilians which have been studied normally incubate their eggs at temperatures above 27 C (Magnusson et al., 1985). Sources of heat for nests include insolation, metabolic heat of embryos, and decomposition of vegetation included in the nest. Incubation temperatures affect the sex of hatchlings (Fergusson and Joanen, 1982, 1983; Webb et al., 1983a; Webb and Smith, 1984; Ferguson, 1985; Webb et al., 1987), post-hatching survival and growth under standardized conditions (Joanen et al., 1987), and influence the preferred temperatures of juveniles (Lang, 1987). Only two species of crocodilians, Paleosuchus trigonatus and Osteolaemus tetraspis, normally inhabit closed canopy rainforest far from large rivers and lakes. These species may face particular problems in maintaining their nests at the high and stable temperatures required by other species of crocodilians because insolation reaching ground level in rainforest may be only 0.5% that recorded outside the forest (Terborgh, 1985). Thermal relations of natural nests of 0. tetraspis have not been studied, but Magnusson et al. (1985) studied the temperatures in four nests of Paleosuchus trigonatus late in incubation. Based on these nests and nine abandoned nests from previous seasons they made the following predictions: