Torrent tree frog  (Litoria nannotis)

Classified as Endangered (EN A2ae) on the IUCN Red List 2004 (1), and as Endangered on both the Queensland Nature Conservation Act 1992 and the Commonwealth Endangered Species Protection Act 1992 (3).

The torrent tree frog is a moderately large, robust species of Australian frog, which at first glance possesses only the typical olive-green skin characteristic of many frog species. On closer inspection, however, it can be distinguished by the extensive dark mottling found across the back and an attractive metallic blue sheen spanning the sides of the body. Additionally, the underbelly is white or cream, the armpits and the groin flesh coloured, and the throat brown. The skin on the back and underbelly has a granular surface; certain individuals possessing small warts scattered across their back. Finger and toe discs are large, with fully webbed toes but only basal webbing on the fingers (4). Males have well developed nuptial pads with small spines on their thumbs and chests so they can cling to females during breeding and avoid being swept off by the turbulent waters of their habitat. Males lack a vocal sac, and the mating call has been described as a slow growl-like sound that is difficult to hear above the sound of flowing water (5).

Litoria nannotis was formerly found throughout the Wet Tropics Bioregion of north Queensland, from Paluma to Cooktown, but is now absent from most upland sites (4).

The torrent tree frog is a stream dwelling species, inhabiting areas of rainforest where there is fast-flowing water, cascades and waterfalls at altitudes of between 180 – 1,300 m above sea level (6). Normally found on boulders near waterfalls, the torrent tree frog is occasionally seen amongst vegetation next to streams (7).

Unusually for frogs, the torrent tree frog is active during the day as well as at night. It does, however, remain close to the protective shelter of the stream during the day, only venturing into more exposed positions in the surrounding vegetation at night (8). In contrast to most stream-breeding frog species that live in adjacent forests, the stream is the primary habitat for both males and females throughout the year, with adults and juveniles noted on several occasions to form small aggregations (four to six individuals) amongst large boulders. Gravid females and males with nuptial pads are found all year round, and it is thought that breeding is possible at any time of the year. Un-pigmented eggs are laid in gelatinous egg masses under rocks in water (1). Adult torrent tree frogs are opportunists with a generalist diet, feeding on both aquatic and terrestrial invertebrates (8).

The reason for the decline of this frog is most likely due to the disease caused by the amphibian chytrid fungus (Batrachochytrium dendrobatidis) (9). Habitat destruction poses no threat, as the Wet Tropics Heritage Area of Queensland that the torrent tree frog inhabits has been protected and undisturbed since 1988 (1) (7). The effects of drought, floods, and pollution have also been ruled out as contributors to the decline (1).

A recovery plan for this species has been developed (10). As the cause of its decline is uncertain the recovery plan focuses on protection of remaining populations and their habitat, population monitoring, and research into its ecology and the disease. Indeed, unless the determinants of this decline are accurately identified and appropriately dealt with, the future of this species cannot be safeguarded.

View information on this species at the UNEP World Conservation Monitoring Centre.

For further information on this species, see:

• Amphibiaweb:
  http://elib.cs.berkeley.edu/aw/index.html
• Frogs Australia Network – Australian Frog Database:
  http://frogsaustralia.net.au/
• Australian Government:
  http://www.deh.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=1817
• Queensland Government.:
  http://www.derm.qld.gov.au/wildlife-ecosystems/wildlife/threatened_plants_and_animals/endangered/waterfall_frog.html