Male and female gray tree frogs.  JAllen photo.

Male and female gray tree frogs. JAllen photo.

To my delight, I came upon this pair of gray tree frogs (Hyla versicolor) on the sidewalk at a convenience store one morning this May.   I nearly missed seeing them and was VERY glad I did or I would have stepped on them!  Gray tree frogs have the ability to camouflage themselves, changing color to blend into their background as much as possible.  On the gray sidewalk, the female, larger frog on the bottom had changed to a palette of gray and black tones as you can see in the photo.   The smaller male on top has retained more green coloration.   The species name of this beautiful frog, ‘versicolor’, comes from its ability to change coloration.

Finding this charming pair made me interested in learning more about their biology and habits.  Nocturnal for the most part, these two probably got caught out in the open by mistake, after leaving their usual tree-top environment for mating.  After finding them on the sidewalk, I moved them off to a moist, shady area in the grass, closer to the trees nearby.  I didn’t want them to get stepped on or fried by the sun when it reached their resting spot.

The gray tree frog is native to much of the eastern United States and parts of southern Canada.  It is not found in southern Florida or in most of Maine.  Look for them in forested areas that are near water or that contain either seasonal or permanent bodies of water.  They leave the trees for mating, which is most active in spring but extends into August, so this is the best time to see them.  Gray tree frogs mature and begin to mate at the age of 3 years.  Females lay as many as 1800 to 2000 eggs on the surface of shallow water.  Bundles of 10-40 eggs are attached to vegetation.  Tadpoles hatch in 4-5 days and metamorphose into little green frogs after about 2-2 ½ months.  As the little frogs grow, their color changes from bright green to various shades of green and gray, usually mottled.  Adult frogs have rough, bumpy skin.

Gray tree frog tadpole (Univ. of RI photo)

Gray tree frog tadpole (Univ. of RI photo)

Females are larger than males and have a lighter colored ‘chin’. The male chin is darker because they have sacs in their throats for calling during mating season. Females do not have a call. Listen to the call of the gray tree frog! The inner thigh is bright yellow-orange and is visible during jumping. This can confuse predators and hopefully deter them! There is also sometimes a dark-edged light spot just below their eyes. Adult frogs are 1 ¼” to 2 3/8” long at maturity.

Newly metamorphosed gray tree frog. Univ. of RI photo.

Newly metamorphosed gray tree frog. Univ. of RI photo.

Gray tree frogs can survive cold temperatures as low as -8° C (17.6° F) and overwinter under logs or debris on the forest floor.  In addition to moving to a protected, insulated place, they keep some of their blood from freezing by producing ‘antifreeze’ in the form of glycerol.  About 40% of their bodies and fluids can freeze without harmful effects.

While gray tree frogs are not considered an endangered species, frog and toad numbers are steadily declining in many areas due to pollution and habitat loss.  It is important to monitor their populations and work to preserve their habitats. In Connecticut, the decline of the gray tree frog was noted as early as 1937.  A main reason for this is the loss of shrubby swamps which is their preferred breeding habitat. When land is developed for residential or commercial use, there is a legal requirement not to lose wetland acreage, but often the desirable shrub swamp habitat is either drained or converted to ponds and small lakes in this process.  These new wetlands often contain fewer species of amphibians and reptiles that are hardy enough to adapt to the new environment.

J Allen