these delayed metamorphs is lower, and the evolutionary utility of this delayed metamorphosis is uncertain. It may be related to the prevalence of fire in their natural ecosystem. During the final stages of transformation when the tadpoles have four limbs and a tail, they stop feeding for a short time while their mouths widen and their digestive systems adjust from herbivorous to carnivorous. For the most part, Pacific tree frogs are nocturnal, but they have been spotted during the day. These frogs spend a lot of time hiding under rotten logs, rocks, long grasses, and leaf litter, where they are very difficult to see unless they move. When they hunt, their toe pads allow them to climb on vegetation and other surfaces where they are to ambush their prey. Much of their diets consists of spiders, beetles, flies, ants, and other insects and arthropods; they can and do eat insects that are almost as large as they are, and will expand their bodies slightly to accommodate these meals. Pacific tree frogs mature quickly, and usually mate the season after metamorphosis. Predators include snakes, raccoons, herons, egrets, and other small mammals and reptiles. When they sense potential food nearby, they commonly twitch a toe to attract it within easy reach of their tongues. They can live up to 8 years in captivity. They produce several call types. These include the males' advertisement call, commonly described as "ribbit" or "crek-ek", as well as an encounter trill call. The cre-ek call can be quite loud and can thus be heard from very far away. Males also produce a "dry land call", a long cre-ee-ee-eeek, that can be heard anytime in the year except during the coldest and driest periods. Pacific tree frogs are the most commonly heard frogs along much of the West Coast of the United States. Green and brown color morphs Previously, adults were thought to occur in two different fixed colors: green and brown. Now, some of them have been found to be able to change between the two. They can also change from lighter to darker, shift from patterned markings to pure colors and vice versa, and even display combinations of colors, brown/green being the most frequent. These color-changing morphs are triggered not by color change in their environments, but a change in background brightness. This type of environmental change would be caused by seasonal fluctuation. A full change