Nesting ecology of the Paraguayan Caiman (Caiman yacare) in the Pantanal of Mato Grosso, Brazil / Peter Gransden Crawshaw Junior.

Tese (Mestre)-- University of Florida, 1987.

A total of 160 nests of the Paraguayan caiman (Caiman yacare) were studied during tehe course of 6 nesting seasons (1979-1983) in two areas in the pantanal of mato Grosso, Brazil. Although c. 400 km apart, the two areas (Pocone and Miranda) were similar with regard to environmental factors. The main difference between them was that Pocone caimans had been intensively hunted until 1974, while no hunting had occurred in Mirenda. The reproductive season started with courship in late August, in the early dry season, and ended in mid-April, toward the end of the wet season. Male contribution to reproduction terminated with copulation. Females selected secluded, shaded sites close to water, and built mound nests in which they deposited an average of 30 eggs. The incubation period, as estimated from embryo growth, was about 65 days, during which the 24 cm embryos grew at a rate of approximately 0.37 cm per day. There was a marked difference in the frequency of female nest guarding between the two areas. This was most likely due to the difference in hunting pressure on the two populations. Pocone females were present on 12.3% of 437 visits to 82 nests, wheres in Miranda females were present on 60% of 397 visits to 49 nests. As a result, nesting success and the probability of hatching in Miranda were three-fold that of Pocone (0.61-0.76 and 0.18-0.15, respectively). Egg predation, mainly by coatis and crabeating foxes, was the main mortality factor ata both sites. However, 78% of the 1980 Pocone nests were destroyed by floods. Recruitment was 4.5 hatchling per female in Pocone and 13.8 in Miranda, with a combined total of 8.4 hatchlings per female in the two areas. There are indications that, if well managed, caimans can be an additional source of income to ranchers in the Pantanal.