Tree frogs have large finger and toe pads which enable them to climb vertical surfaces like tree trunks, so many of them have taken to an arboreal life, as their common name suggests.
Tree frogs are mostly found throughout the Americas and in Australia. There are also some species in Eurasia and Africa. Most of them live up to their names and live in trees but some, especially desert hylids, live at ground level or burrow. Most species live in rainforests, with over 40 species being found in the Amazon basin alone.
There are almost a thousand described species of hylids but many are endangered and one is considered to be extinct. The tree dwelling species have large forward facing eyes and binocular vision but in burrowing species, the eyes are reduced.
In general, tree frogs are active at night and hide during the day. They come out at dusk to eat insects and look for love. Tree frogs have beautiful froggy voices and love to sing. The green tree frogs that live around my home live in the drainpipes because their calls echo inside like a didgeridoo. They get so noisy when it is raining that we cannot hear the TV. They will also crawl out on the roof and then launch themselves into space, hitting the ground with a jelly-like quiver. It is a long way down, but it doesn’t seem to hurt them. They are large frogs and consume great quantities of insects and spiders which more than makes up for their noise.
Hylids, like all frogs, have to maintain a connection with water in order to reproduce. They lay their egg masses in water and these hatch into normal froggy tadpoles. Like many tadpoles in Australia, tree frogs are threatened by the spread of cane toads. Not only are cane toad adults poisonous but cane toad tadpoles are carnivorous and attack other tadpoles. As cane toads spread, other species of frogs become rarer and disappear. Some of the rainforest hylids use water trapped in bromeliads or tree hollows to lay their eggs. A few have tadpoles with suckers to attach themselves to rocks so these hylids attach their eggs to rocks in fast flowing streams. Others attach their eggs to leaves overhanging ponds so the tadpoles can drop into the water when they hatch.
Hylids are divided into three subfamilies. The Australian and New Guinea species are grouped in the Pelodryadinae. This group includes one genus of burrowing frogs, the Cyclorana. The leaf frogs of the Americas are in the Phyllomedusinae and the rest form the Hylinae which includes a wide variety of genera and species, including cricket frogs and another group of burrowing frogs, the Smilisca, which occur from Texas to Central America.
As with all common names, one has to be careful. There are frogs called tree frogs that are not Hylids and there are hylids which do not live in trees. Frogs that are classified as Hylidae have an unfused pectoral girdle and in most species there is cartilage between the last two bones of each finger and toe. They also have maxillary teeth. You don’t have to be that exact though. If you see a frog in a tree, feel free to call it a tree frog!
References:
http://animals.jrank.org/pages/184/Amero-Australian-Treefrogs-Hylidae.html
Cogger, H. 2000 Reptiles and Amphibians of Australia
http://en.wikipedia.org/wiki/Hylidae
