Cope's Gray Treefrog
Summary: Common in the oak savannas of the Fox River valley in Kane, McHenry, Lake, and Walworth Counties. The exact limits of the range are uncertain.
Description: This is a medium sized (1.25 to 2.25 inches; 3.2 to 6.0 cm) tree frog, with a robust body form and slightly roughened skin. It is usually some shade of light green or pale gray, with or without an irregular lichen-like blotch on the back. The same frog may be dramatically different colors at different times. There is usually a light spot under each eye, and bright yellow-orange flash colors with black mottling on the concealed surfaces of the hind legs. Toe pads are readily visible.
Hyla chrysoscelis is a diploid form, distinguishable from the tetraploid Hyla versicolor only by call or by chromosome count or cell size.
Distribution and Status: Cope's gray treefrog is relatively common in the Fox River Valley of Kane, McHenry, and western Lake Counties, and into southern Wisconsin. Otherwise, the regional distribution is not well known. It appears to be absent from the southern and eastern parts of the region, where it is largely replaced by the sibling species Hyla versicolor. However, Cope's gray tree frog is known from Berrien County, Michigan, and not all treefrog populations in the Chicago region have been positively identifed at this time.
Habitat: Most populations are associated with oak savanna, occasionally with slightly denser woodlands. Breeding occurs in marshes, with males usually perched in low shrubs or among herbaceous vegetation but sometimes on the shoreline or in the water. At some sites frogs call from different wetlands in different years. At one site a shallow man-made borrow pit was utilized, and at another a low shrub bog provided calling sites for some frogs. Although an occasional treefrog is found on the ground during the day, most individuals climb into shrubs and trees. I have heard gray treefrogs call from the tops of 75-foot tall bur oaks.
Voice: A fast, harsh buzzing call, faster and lower pitched than the call of Hyla versicolor.
Phenology: Although surface activity may begin in April, breeding usually does not commence until mid-May, when evening temperatures remain above about 55 degrees F. Sporadic calling can continue into early summer, especially before and after rainfall. There is little local information on larvae, but presumably metamorphosis occurs in mid-summer. Juveniles are not often seen.