Western Chorus Frog
Pseudacris triseriata
Summary: This habitat generalist occurs in every county in the region, and at most inventoried preserves. It is especially abundant in former prairie and savanna areas. In heavily forested parts of the Indiana Counties populations are more widely scattered.
Description: A small frog, about 1.0 to 1.5 inches (25-37mm), tan to brown with a series of longitudinal darker stripes. Three of these are on the dorsal surface; there is also a stripe running through the eye and the length of each side. Individual frogs have a lighter ground color and a distinct pattern at warmer temperatures; frogs observed in cold water in early spring are usually dark brown, with the stripes visible but indistinct.
The underside is white. Toe pads are present but difficult to see except with magnification. Males have a yellow throat, most obvious in the spring.
Under most circumstances, the western chorus frog is not easily confused with any other local frog. No other species found in the region has stripes running the length of the body. Rare individuals may have the dorsal stripes broken into blotches; cold and dark frogs may require close inspection to see the pattern.
Distribution and Status: Western Chorus Frogs are possibly the most common and widespread amphibians in the Chicago region. They remain abundant even in predominantly agricultural and suburban regions as long as small pockets of wetland remain intact. In the most heavily forested areas, especially in Indiana, they may be absent but usually occur not far away on open sites.
Habitat: The only requirements of this habitat generalist seem to be dense herbaceous vegetation and temporary wetlands for breeding. Although western chorus frogs were probably originally most abundant in savanna and grassland ecosystems, today they occur in most habitat types. The most frequently encountered situation is successional field, usually former farmland, with sparse tree and shrub cover and shallow cattail marshes. The ability to utilize relatively ephemeral breeding wetlands is a key element of the adaptability of this species. Except for breeding, the species is entirely terrestrial.
Wooded sites are also utilized, including floodplain forest, upland woodland, and flatwoods, although abundance may not be as high there. I have not seen the species in active cropland, in densely populated residential areas, or in the most extensive mesic beech-maple forests in Indiana; in the latter habitat it is replaced by the spring peeper.
Voice: The call may be imitated by running a thumbnail down the last 20 small teeth of a plastic pocket comb. It carries well, and is often heard at distances of a quarter-mile.
Phenology: This is one of the first amphibians to become active in the spring. Calling has been reported as early as March 1, although in a typical year it begins in mid to late March. The shallow breeding wetlands, usually open and sunlit, warm quickly in early spring. Small egg masses are attached to submerged sticks or vegetation in late March or April, with a relatively prolonged breeding period usually lasting into early May. I have heard sporadic calling through June. The small tadpole develops quickly, and may leave the water as early as mid-June. Juveniles and adults forage in herbaceous vegetation surrounding the breeding sites. They are easily observed in the wet grass after summer rainfall, even during the day. In October individual males are sometimes heard calling weakly from terrestrial locations.
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| Updated: October 9, 2007
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