Effect of Habitat on Survival of Eggs and Sex Ratio of Hatchlings of Caiman crocodilus yacare in the Pantanal, Brazil

Abstract

Flooding of nests and predation were identified as the major mortality agents of eggs of Caiman crocodilus yacare in Brazil. Nests on floating grass mats and in forests were flooded in 1989, but only floating grass mats nests were flooded in 1990. Predation on eggs was high in forest nests, but my presence may have increased predation. No nest on floating grass mats was attacked by predators. The period of sex determination of C. c. yacare can extend to 40 d of incubation. I predicted nest temperature with a multiple regression model incorporating weather variables during incubation. The predicted nest temperatures for nests on floating grass mats and nests in forest were correlated with the sex ratio of the clutch. High nest temperatures (> 31.5 C) produced mostly males, and low nest temperatures (<30.5 C) produced only females. The estimated sex ratio varied between years in nests on floating grass mats, but not in forest nests. Estimated nest temperatures significantly affected the snout-vent lengths of hatchlings but not their masses. Fifty percent of nesting occurred on floating grass mats, so the destruction of this habitat by introduced animals such as the water buffalo (Bubalus bubalis) will adversely affect the productivity and hence long-term density of caimans in the Pantanal.