within a species may change with age, sex, and season, and may also differ between populations. In many species, juveniles are generally carnivorous but become more herbivorous as adults. With Barbour's map turtle, the larger female mainly eats mollusks while the male usually eats arthropods. Blanding's turtle may feed mainly on snails or crayfish depending on the population. The European pond turtle has been recorded as being mostly carnivorous much of the year but switching to water lilies during the summer. Some species have developed specialized diets such as the hawksbill, which eats sponges, the leatherback, which feeds on jellyfish, and the Mekong snail-eating turtle. Communication and intelligence While popularly thought of as mute, turtles make various sounds to communicate. Tortoises may bellow when courting and mating. Various species of both freshwater and sea turtles emit short, low-frequency calls from the time they are in the egg to when they are adults. These vocalizations may serve to create group cohesion when migrating. The oblong turtle has a particularly large vocal range; producing sounds described as clacks, clicks, squawks, hoots, various kinds of chirps, wails, , grunts, growls, blow bursts, howls, and drum rolls. Play behavior has been documented in some turtle species. In the laboratory, Florida red-bellied cooters can learn novel tasks and have demonstrated a long-term memory of at least 7.5 months. Similarly, giant tortoises can learn and remember tasks, and master lessons much faster when trained in groups. Tortoises appear to be able to retain operant conditioning nine years after their initial training. Studies have shown that turtles can navigate the environment using landmarks and a map-like system resulting in accurate direct routes towards a goal. Navigation in turtles have been correlated to high cognition function in the medial cortex region of the brain. Defense When sensing danger, a turtle may flee, freeze or withdraw into its shell. Freshwater turtles flee into the water, though the Sonora mud turtle may take refuge on land as the shallow temporary ponds they inhabit make them vulnerable. When startled, a softshell turtle may dive underwater and bury itself under the sea floor. If a predator persists, the turtle may bite or discharge from its cloaca. Several species produce foul-smelling chemicals from musk glands. Other tactics include threat displays and Bell's hinge-back tortoise can play dead. When attacked, big-headed turtle hatchlings squeal, possibly startling the predator. Migration Turtles are the only reptiles