Common name: cascade treefrog
Scientific name: Litoria pearsoniana
Family: Hylidae (treefrogs)
Conservation status: This species is listed as Vulnerable in Queensland (Nature Conservation Act 1992). It is ranked as a low priority under the department's 'Back on Track' species prioritisation framework.
The cascade treefrog is a small frog; males have a snout-to-vent length of 24–29mm and females 31–37mm. Their colouration is highly variable and can change seasonally. Colouration ranges from green, through various combinations of green and brown to dark brown, with or without black spots or darkly marbled and blotched.
A thin pale stripe runs from the nostril, through the eye, passes above the tympanum (external ear) and continues along the flank to the midbody. This stripe is bordered below by a brown band, broadening as it extends along the flank to the midbody. There may be a pale stripe along the upper lip. The tympanum is distinct and brown in colour.
The cascade treefrog has a white or cream belly. The hidden parts of the groin and thighs are yellowish tan to brick red. The skin is smooth or rough above, granular below. The limbs have well developed disks, but only the toes have extensive webbing.
Habitat and distribution
The cascade treefrog inhabits streams in rainforest and adjacent wet sclerophyll forest at elevations of 200–1000m in south-eastern Queensland and north-eastern New South Wales (NSW). It is found in wet forest between Lismore, NSW and Kenilworth, Queensland. A disjunct population of this species group, located further north at Kroombit Tops, has since been described as a new species (Litoria kroombitensis) in 2013 (Hoskin et.al. 2013).
Genetic research indicates there are two distinct populations in south-eastern Queensland separated by the Brisbane River valley. A southern population occupies the Gibraltar, Main and Border Ranges, and a northern population in the D'Aguilar and Conondale Ranges.
Life history and behaviour
During spring and summer adult males are located under logs, rocks, rotting leaf litter and moist soil cavities adjacent to the water edge during the day. They emerge at night to call from rocks, low vegetation, and debris in or near streams. During winter, frogs may form large mixed sex aggregations to hibernate in humid crevices with relatively stable temperatures. Here they form closely packed groups, adopting a compact pose with dorsal and ventral surfaces pressed against the crevice surfaces to reduce surface area. Individuals are lethargic with eyes closed.
The mating call is a diphasic three note call lasting for 0.8 to 1.8 seconds with a "weeeak kuk kuk" sound. Variations include; a very slow version of the first part of the call heard early in the evening, or the first part of the call is made by one male and answered by a second by completing the sequence, or individuals may merely repeat the last two notes several times.
Reproductive activity occurs from August to April, peaking from October to early February. Females may possess the ability to breed more than once a season.
Mating takes place near oviposition (egg-laying) sites. Eggs are deposited as a clump of 363–732 eggs attached to rocks, debris or aquatic plants in still, shallow pools adjacent to, or connected with the main stream. The eggs are dark, 1.1–1.3mm in diameter and are covered in a clear jelly capsule 3.0–3.5mm in diameter, generally obscured by grey or brown silt. Eggs hatch 3–5 days after spawning, with metamorphosis (from tadpole to frog) typically occurring 2–2.5 months later depending on temperatures.
Tadpoles are a light golden colour during early stages, darkening to brown, and some specimens develop dark spots in the later stages. The belly surface is not pigmented. The body is broader than deep, with the greatest breadth behind the eyes. The tail is moderately thick and has a rounded tip. The fins are transparent with dark spots.
The cascade treefrog experienced significant population declines in the late 1970s and 1980s, with some populations disappearing. Monitoring indicates populations have recovered at some sites. The causes of this and similar declines in the upland rainforest frog fauna of south-east Queensland are almost certainly due to the amphibian chytrid fungus, which has been found in sick and dying individuals of this species.
Suspected threatening processes include:
- Destruction of winter aggregation sites through clearing of habitat, timber harvesting and urban development.
- Degradation of water quality and riparian vegetation arising from logging, grazing, weed invasion and pollution.
- Predation by feral pigs.
The recovery plan makes the following management recommendations for the conservation of stream frogs of South-east Queensland:
- Monitor historical localities to detect recovery.
- Investigate disease in preserved animals and species occupying similar habitat.
- Develop and refine husbandry techniques for rainforest stream dwelling frogs.
- Continue studies on the ecology of this species.
- Train park staff and community volunteers in identification of this species.
- Implement monitoring by park staff at select locations within the national park estate where L. pearsoniana occurs.