Amphibians
American Green Tree Frog
Dryophytes cinereus · also called American green tree frog, green tree frog, bell frog
The American green tree frog is the small, sleek, bright green frog that turns up on a lit window screen on a summer night in the American South, picking off moths. It is one of the region’s most familiar animals — a backyard frog, a beloved pet, and the source of the ringing, cowbell chorus that means summer near any Southern pond.
Overview
American green tree frogs live along wetland edges, in floodplain forest, and in suburban ponds and gardens across the southeastern and south-central US, and the species is spreading north. They are nocturnal, arboreal, and closely tied to water for breeding. Adults are usually a crisp bright green with a white or cream side stripe and scattered gold flecks, though the green can dull to grey-olive.
Colour and grip
The frog can shift its colour slowly between bright green and dull olive with temperature, light, and stress — a limited camouflage. Its toe pads, coated in mucus and patterned with micro-ridges, grip leaves, bark, and glass through wet adhesion, so it readily climbs house windows.
The call
Males give a nasal, bell-like “quonk” from waterside plants, up to about 75 times a minute on warm humid nights; a full chorus rings like distant cowbells — the old name “bell frog.” A separate harsher “rain call” comes from trees and gutters before wet weather.
Status
The American green tree frog is Least Concern, common, adaptable, and in places expanding. It is the state amphibian of Georgia and Louisiana and one of the most kept pet frogs in North America.
American Green Tree Frog: common questions
Why is the American green tree frog sometimes grey instead of green?
It can change colour, within limits. The frog's skin contains pigment cells that it can adjust, shifting its overall tone between a vivid leafy green and a dull grey-green or olive over a period of minutes to a couple of hours. The change is driven by temperature (cooler frogs tend to be darker), light level, activity, stress, and to some extent the colour of what it is sitting on. It is not the rapid, precise, pattern-matching camouflage of a chameleon or a flounder — more a slow mood-and-conditions ring — but it does help the frog blend with foliage when active and with bark or leaf litter when resting.
How do tree frogs stick to glass?
The discs on the tips of a tree frog's fingers and toes are covered in a pattern of tiny hexagonal cells separated by channels, and the frog secretes a thin layer of mucus onto them. When the pad is pressed against a smooth surface, the mucus fills the gap and the pad grips through a combination of surface tension (wet adhesion, like a wet sheet of paper stuck to a window) and close mechanical contact between the micro-ridges and the surface. The channels drain away excess fluid so the contact does not simply slip. It works well enough that an American green tree frog can climb a vertical pane of glass and cling to the underside of a leaf.
What does the American green tree frog's call sound like, and why is it called a bell frog?
The male's advertisement call is a short, nasal, honking "quonk" or "queenk," given from a perch in vegetation at the water's edge and repeated rapidly, up to around 75 times a minute on a warm, humid night. When hundreds of males call together the overlapping notes produce a ringing, clanking chorus that early settlers compared to a herd of distant cowbells, which is where the old name "bell frog" comes from. Individual frogs also give a shorter, harsher "rain call" from trees and gutters before or during wet weather, away from the breeding pond.
Is it a good pet, and can you find them in your garden?
American green tree frogs are among the most commonly kept pet frogs in North America because they are hardy, attractive, and inexpensive, and captive-bred animals are available; they need a tall planted terrarium, moderate humidity, live insects, and clean dechlorinated water, and can live around a decade. In the wild, across the Southeast, they are one of the frogs people are most likely to encounter without looking for them — on window screens and porch lights hunting insects, in garden ponds, in flowerpots and downpipes, and calling loudly from any patch of waterside vegetation on a summer night.