Effects of environmental variables on black caiman counts in Bolivia

The proportion of a crocodilian population seen during night spotlight counts (sighting proportion) is affected by environmental conditions. I developed multiple regression models to estimate the sighting proportion of black caimans (Melanosuchus niger) using 7 environmental variables as predictors. Although the models were statistically powerful, their use in long term monitoring programs appeared to be limited, given that changes in density affected the sighting proportion. This finding has implications in the management of wild populations of crocodilians; long-term monitoring programs based on night counts usually assume that, once the environmental effects have been accounted for, the sighting proportion remains constant over time.