SPENCER, Ricky-John; CLARK, William/F; Iowa State University; Iowa State University: Testing a theoretical model of nest site selection in turtles and water birds.

Nest selection has important consequences for fitness in water birds and freshwater turtles, as factors such as nest predation are high in many populations. We developed a theoretical model that balances perceived risk to individual fitness with offspring survival to determine optimal nest site selection in terms of testable factors, such as distance to shore or wetland area. The model uses the law of diminishing returns and predicts that females should nest where any increase gain in offspring survival is equal to any increase in perceived risk to adult survival. We experimentally reduced predation risk in an Australian freshwater turtle and showed that (1) females maximize offspring fitness when perceived risk to adult survival is minimal (2) perceived risk is reduced with age (3) or older females are willing to take greater risks because they are close to reproductive senescence.