The distribution and status of the Giant Burrowing Frog Heleioporus australiacus in the Shoalhaven region of south-eastern New South Wales

Abstract

Surveys were conducted for the Giant Burrowing Frog Heleioporus australiacus within 50 km of Nowra, on the south coast of New South Wales using a variety of methods. Thirty-eight 250 m transects were surveyed at night for 30 min each and 0–12 adult frogs were detected during these searches. Additional diurnal searches for tadpoles proved to be the most efficient method to detect the species and locate breeding sites. Of 102 sites surveyed, fragmented populations were found at 27 by the presence of tadpoles and adult frogs. The vegetation at these sites was woodland and open forest with a dense shrublayer of heath, but was often ecotonal. Forty-six percent of the sites were within 100 m of cliff edges/waterfalls. The lithology of sites where the frog was found varied from Hawkesbury, Nowra and Snapper Point sandstones. The exception was a population south of Ulladulla that occurs on undifferentiated sediments, but at that site exposed sandstone and a sandy overlay was present. The location of tadpoles indicated that adults were highly selective of the section of drainage line used for breeding. Often these sites consisted of a few small pools in non-perennial creeks. Breeding behaviour was associated with late summer and autumn rain, but in some sites reproduction did not occur annually. Based on distribution and habitat preference, the region has five discrete populations. Urban development has fragmented populations.