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The gray treefrog complex consists of two sibling species that are indistinguishable morphologically, the diploid Hyla chrysoscelis and the tetraploid Hyla versicolor. Identification is possible in the field only by audio recognition of male advertisement call trill rates (pulses/second). During 1979-1983 we evaluated taped calls of these two species taken from 89 populations from throughout Virginia to map their respective ranges and to evaluate differences in call parameters. Hyla chrysoscelis occurs in the Coastal Plain, eastern and southern Piedmont, and in southwestern Virginia. Hyla versicoloroccurs in the Piedmont, Blue Ridge, and Ridge and Valley regions south to Wythe and Tazewell counties. Sympatric sites occur in several locations in the Piedmont and both species are syntopic in several of them. Male trill rates are significantly related to Ambient and body temperatures. Rates produced by male H. chrysoscelis (>31/s) are twice as fast as that for H. versicolor (<30/s); they did not overlap in our samples at any temperature. Trill rates and call duration in southwestern Virginia populations of H. chrysoscelis differed significantly from those in eastern populations when adjusted for ambient temperature. Adjusted trill rate and duration in H. Chrysoscelis populations in sympatry with H. versicolor were not significantly different from allopatric populations but were for H. versicolor.