Nature Bulletin No. 79   August 17, 1946
Forest Preserve District of Cook County
Clayton F. Smith, President
Roberts Mann, Superintendent of Conservation

****:TREE FROGS

The tree frog, or "tree toad", is popularly supposed to forecast rain; 
probably because he prefers humid weather and, after the mating 
season, sings only on warm sultry or rainy nights and occasionally on 
dark rainy days. Seldom seen, its clear melodious trill is usually 
supposed to be that of sore bird.

They spend most of the summer in trees and thickets, feeding on many 
kinds of insects, and winter in hollow trees, under stumps, or in other 
cavities.

Like all frogs and toads they must mate and lay their eggs in water. In 
late spring or early summer the tree frogs seek a woodland pool or quiet 
backwater containing aquatic plants and protected by high vegetation 
along the banks. Each female lays 1000 to 2000 eggs in a series of 
small blobs that stick to submerged stems and leaves. In 4 or 5 days 
small tadpoles hatch out. Equipped with gills, they live in the water. In 
45 to 65 days these change into young frogs that promptly go up in the 
trees.

This "metamorphosis" is a gradual and complicated process. They lose 
their rows of horny "baby teeth". The tiny mumbling mouth stretches 
into a grinning gape that can swallow bugs as big as the frog itself. The 
intestine, as the diet changes from algae "hay" to insect "meat', shrinks 
to a fraction of the length that it was in the tadpole. The gills are 
absorbed and the lungs begin to breathe air. The tail is absorbed; it does 
not drop off. The front legs break through the skin that has grown over 
the gills; the hind legs grow long and powerful: so powerful that the 
frog's tremendous leaps make it appear to fly. Its four toes on each front 
foot and the five on each hind foot all have moist discs like suction cups 
at the tips which enable it to cling to smooth surfaces or perform 
astonishing acrobatics.

They are remarkable for their ability to change color but these changes, 
requiring an hour or two, are not made at will to harmonize with their 
surroundings. Apparently these changes are influenced by the 
temperature and humidity. The under side of the thighs is bright yellow 
or orange but the back of the body and legs may be various shades of 
brown, gray or green -- some of them mottled.