Like all amphibians, frogs need moisture. They leave water cautiously and most return to breed. Without moisture, their marvelous skin could not transfer oxygen from both air and water. Frog eggs are most particularly vulnerable to drying out for they have no protective shell.

All frogs are superficially of a simple design; they have few vertebrate ( five to ten) and the bones in their front legs and back are fused. In contrast, humans have 33 vertebrae, our lower arm bones are separated into radius and ulna, and our lower leg bones are separated into tibia and fibula. The two major bones in frogs are fused or partially fused. These particular features are adaptations to leaping and the stress that each landing will place on the skeleton.

The frog skull is a simple structure with virtually no neck, so almost all frogs must move their entire body to look in a different direction. In most species, nature has overcome this limitation by installing large, protruding eyes that provide almost 360- degree vision. Most species of frogs also have sharp eyesight, which helps guide their long tongues when they are capturing prey.

Frogs are ectotherms, which means that they obtain their heat from external sources. In contrast humans are endotherms, with an internal furnace that must be fueled daily to maintain a body temperature of around 37 degrees Celsius. Ectotherms are often called cold-blooded, but this term is a misnomer. Since their body temperature comes directly from the sun or from proximity to a heat source, on warm days ectotherms are warm. Moreover, cold blooded is a pejorative term implying cruelty and malevolence. I suspect, that the brain of a frog, does not contain room for these higher functions.

Because frogs cannot control their temperature internally, they do so behaviorally. During active periods of the year- usually the wet season in the tropics and the warm season in temperate areas- frogs select areas that provide heat but not too much heat. A move to the shade significantly reduces their temperature, as does a move into the water. This temperature control is critical because frogs that are too hot will die and frogs that are too cold will be unable to flee from danger or catch their prey.

Frogs that live in the temperate zone experience at least a few months every year when no source of heat is adequate to meet their needs. So they skip this season by hibernating. During hibernation, which may take place on wet litter at the bottom of ponds and lakes, they are very close to death. During hibernation, a frogs energy reserves remain largely intact for use during the spring to come.

Adaptations specific to Tree frogs

Treefrogs are obviously climbing frogs. They have special toe pads that allow them to cling to leaves, twigs, and tree trunks. Yes, what put the tree into treefrog? The toe pads did. Toe pads allow treefrogs to climb. Toepads are large, rounded tips on the treefrogs toes. The pads make it possible for treefrogs to cling to branches, leaves, or even glass. When a treefrog jumps onto a leaf, the toepads keep the treefrog from falling off. Toe pads are moist. This moisture allows them to cling to smooth surfaces. The moisture on toe pads is not sticky like glue. It is mostly water. Water can hold things together on its own.

Treefrogs can quickly change the tone of their skin from light to dark. Warmth and light backgrounds can make them turn light. Cold and dark backgrounds can make them turn dark. A few treefrogs can change colors. Gray tree frogs can turn from gray to green to blend in with leaves. The lemur treefrog can turn from a reddish color to green. Barking tree frogs can change from plain, bright green to green with dark spots. Most tree frogs are colored for camouflage. Their patterns and colors help them blend in with lichens, stones, leaves, or bark. The camouflage keeps them safe from birds and other predators that hunt by sight.

Tree frogs have big eyes to help them see better at night. Tree frogs are nocturnal, which means they are active at night. They find their prey by sight. They also make giant leaps from one twig to another. It takes a good eye to land safely. Big eyes can open wide to let in a lot of light. Large eyes also mean big retinas. The retina is in the back of the eye. It senses light and sends messages to the brain. A big retina helps a frog see in low light. The colored part of a treefrogs eye is called the iris. It opens wide in the dark of night to let in more light. It closes to a slit during the day to protect the eye from too much light.