Mass nesting of olive ridley sea turtles Lepidochelys olivacea at La Escobilla, Mexico: linking nest density and rates of destruction

Olive ridley sea turtles Lepidochelys olivacea exhibit synchronized nesting behavior that affects egg survival through a variety of mechanisms, including intra-specific nest destruc- tion. This activity is difficult to quantify due to the frequency of arribadas (mass nesting events that occur over several days) and temporal overlap of incubation periods. We hypothesized that nest destruction is positively related to cumulative nest density. We quantified these variables through direct observation of nesting by 1293 turtles in 26 plots (each 9 m 2 ) during 2 arribadas at La Escobilla, Mexico, in 2009. Cumulative nest densities ranged from 1 to 8 nests m �2 . The propor- tion of turtles observed destroying eggs was used as a proxy for nest destruction. A total of 5.12 and 23.10% of turtles destroyed eggs in the first and second arribadas, respectively. We used a mixed model logistic regression to determine that the odds of destruction (or the probability that a turtle destroys eggs divided by the probability that she does not) increased 21% for every addi- tional nest per square meter. We could not measure total egg survival as a function of nest density likely due to extreme weather conditions and beetle predation that resulted in 0% hatchling pro- duction over most of the study area in August to October 2009. However, understanding the rela- tionship between nest density and the probability of nest destruction is an important first step toward quantifying density dependence in olive ridleys. We recommend that monitoring plans include standardized measurements of density (nests per square meter) and destruction levels to improve estimates of annual hatchling production.