Isla Cañas is one of a handful of places that olive ridley sea turtles nest in high numbers (the others are two beaches on the Pacific side of Costa Rica and two beaches in Orissa on the Bay of Bengal in India). Endangered species including the hawksbill, loggerhead sea, leatherback and green turtle nest here too. The turtles nest from July through early November, though peak months are usually September and October.
Bring a mosquito net and lots of insect repellent, long pants, a windbreaker or bug jacket and mosquito coils if you have them.