Red-thighed frog, or Quacking frog. The Harold Cogger book "Reptiles and amphibians of Australia" describes the Crinia georgiana Tschudi 1838, or Tschudi's froglet.
Photo from Google Images (flickr.com), and "Heard" on our walk 10 July 2014, near Serpentine Falls.
Description: Uniform brown above, or with irregular scattered dark brown spots or marbling, or sometimes with dark brown dorso-lateral stripe on each side enclosing a lighter vertebral region. A dark strip from the nostril, through the eye to the groin. Limbs with darker cross bars. Axilla, groin and hind side of thighs bright red. Ventral surface dull white or brownish, often with a white median line. A white spot on the base of each arm. Throat of male dark brown. Skin smooth or with warts and skin folds above, coarsely granular below. Vomerine teeth (upper surface of mouth) for holding prey, usually present. Toes without fringes or expanded tips. 40mm.
Distribution: Wide if patchy distribution through coast and adjacent areas of south-western WA, from Carnarvon district in north to Esperance district in south east.
Habit: Inhabits marshy areas from shallow bogs and marshes to saturated vegetation beside small streams , gutters and seeps in forest areas. Main records that the species is a winter-spring breeder and that the call is a “quack…quack…quack”.