Nest Predation - Costa Rica

Raccoon Predation

For millions of years, mother sea turtles have been visiting the terrestrial environment just to lay their eggs. Usually arriving near high tide, most likely in order to reduce the distance traveled on the beach, a female turtle drags herself onto land and finds a suitable place to make her nest. Sometimes such a place is not found and the turtle simply turns around and leaves, this is called a false crawl, or she goes ahead and digs a nest anyway. A turtle may undertake this arduous task multiple times within the same nesting season. Each species undergoes these nesting activities in their own way. Leatherbacks dig deep nests for their eggs and then make several large body pits by disturbing nearby areas in order to conceal the true location of the nest. Olive Ridleys are quicker and dig shallow nests. After laying her eggs, an Olive Ridley will cover the nest by packing sand down on top of it. Alternating her rear flippers in a sort of stomping motion, she rocks side to side and performs what we fondly call the “Ridley Shuffle.” Average nest depth, clutch size, egg size, incubation period, and nest attempts vary widely from species to species. However, they all share some fundamental characteristics. They all must come on land to nest and parental care is non-existent. This life-history strategy has its pros and cons. It allows for more energetic investment in additional offspring, rather than expending that energy in raising young. Millions of eggs are produced with the safe bet that some will survive into adulthood, yet many do not last that long. Many do not even get a taste of the ocean waters.

One of the major quandaries facing sea turtle populations is nest predation. Shallow nests are breached by dogs, raccoons, coatis, crabs and even ants shortly after being laid. Hungry for the nutritious yolk, these animals devour turtle eggs and leave remaining eggs exposed and susceptible to infection. If given sufficient time to incubate, emerging hatchlings are then vulnerable to further predation by those same creatures which now include predatory birds. If they manage to avoid predators as they cross the beach and are not disoriented by human caused light pollution, arrival at the sea introduces a host of new and threatening dangers. This is why turtles invest so much energy into producing as many offspring as possible. The trade-off is that they are unable to care for their young. That is where biologists and conservationists like myself come in. In a form of altruistic behavior, we sacrifice our time and strength for the unrecompensed benefit of sea turtles. Here at Playa Grande we have a turtle hatchery, where nests that have a higher risk of predation or being drowned by rising tidal waters can be relocated. We have developed a system to protect these relocated nests by deterring unwelcome predators. In the hatchery, and under our watchful eyes, turtle eggs are in a safer location and can grow up unmolested by predatory critters. Our work in the hatchery helps minimize the loss of nests by predation and augments the number of hatchlings that enter the ocean.

Predated Nest

Dog Predation