Northern Corroboree Frog

Population and DistributionExamination of museum records indicate that P. pengilleyi (recorded at the time as the northern form of P. corroboree; see Pengilley 1966; Osborne et al. 1996) was most frequently collected in the Brindabella and Bimberi Ranges near Canberra. Specimens were examined from Snowy Flats, Ginini Flats, Bulls Head, Lees Spring, Coree Flats, California Flats and Hume Sawmill. Osborne (1989) found that the species was still present at most of these sites but was unable to find frogs in the vicinity of Hume Sawmill at the n. extremity of its range. Osborne (1989) also found the species to be widely distributed and common throughout the Fiery Range and Bogong Mt. [Osborne et al. 1999]Studies in 1991 on the genetic structure of Pseudophryne populations revealed that the southern population of P. corroboree was in fact a separate species from the two northern populations, which then became known as the species P. pengilleyi (Osborne & Norman 1991). Hybridisations between the two species were found to result in high mortality of larvae (Osborne & Norman 1991). Pseudophryne pengilleyi occurs in two allopatric populations (Osborne 1989). The Fiery Range population occurs from Yarrangobilly to Buccleuch SF at 960-1520 m, an area of occurrence of about 550 km2 (Osborne 1989). The Brindabella Range population occupies only 60 km2 from California Flats to Mt Bimberi at 1090-1840 m (Osborne 1989). Between 1994 and 1998, restricted surveys were undertaken (mainly along vehicle tracks) throughout the known range of P. pengilleyi in the Fiery Range and Bogong Mt. More extensive surveys were conducted in the Brindabella Range and Bimberi Range (Osborne & Hunter unpubl. data). The species was still relatively abundant and widespread in the Fiery Range, however, was not found in the Yarrangobilly-Peppercorn Hill area where it was previously recorded by Pengilley (1966) and Osborne (1989). The species was found at breeding sites (often remote from each other) throughout suitable parts of the Brindabella and Bimberi Range, both in the ACT and contiguous areas of NSW (Osborne et al. 1999). The numbers present at breeding sites in the region were considerably lower than was recorded by Osborne (1989 and unpubl. data).[Osborne et al. 1999]Long-term monitoring of P. pengilleyi was only undertaken in the Brindabella Range. Only one population, Ginini Flats - a subalpine site (1600m) in the ACT was subject to annual monitoring. Numbers present at Ginini Flats declined substantially during the first few years of monitoring and have remained low ever since. Less-regular monitoring was undertaken at Coree Flats (980m) in NSW. By contrast, the Coree Flats population has supported a larger number of calling males (at least during the years the survey was carried out). However, monitoring at Coree Flats commenced after a major drop in numbers had occurred at other sites. Earlier collecting and observations by Pengilley (1966 and pers. comm.) at this site indicated that the population was very large (perhaps over 500 individuals). The low numbers detected in 1998 are likely to be a direct response to the extreme drought conditions prevailing during the breeding season.[Osborne et al. 1999]Pseudophryne pengilleyi has declined at higher altitudes (above 1400 m) but remains common at montane altitudes in the Fiery Range (Osborne et al. 1999). The species is known from Namadgi National Park, ACT, Kosciuszko NP, NSW and Buccleuch SF.HabitatPseudophryne pengilleyi is restricted to montane and subalpine woodlands, heathland and grassland above about 1000 m (Osborne 1990a). The species prefers to breed in Sphagnum bogs and wet heath in subalpine areas and dense patches of herbs in openings or seepages amongst fallen tussocks at lower elevation (W. Osborne pers. comm.). Non-breeding habitat occurs in forest, woodland and heath adjacent to breeding sites (Osborne 1990a).

ReproductionPseudophryne pengilleyi breeds in bog pools at high altitudes (above 1400 m) and in shallow seepage pools in gullies at lower altitudes (1000-1400 m) (Osborne 1990a). Osborne (1990a) summarised the main features of the reproductive ecology of P. pengilleyi (after Pengilley 1966, 1971, 1973; W. Osborne unpub. data.). Field measurements (Pengilley 1973) suggest that the species reaches sexual maturity at three years of age (ie. one year as an embryo/tadpole and two years as a juvenile/subadult) which is consistent with observations of captive reared individuals (Osborne 1990a). It is unlikely that many adults survive for more than one breeding season (Osborne 1990a). Breeding occurs from Jan. to Mar. (Pengilley 1966, 1973; W. Osborne unpub. data.) and 16-40 eggs (Pengilley 1973) of ovum diameter 3.1-3.6 mm (capsule diameter 6.0-10.0 mm W. Osborne unpub. data.) are deposited terrestrially (Pengilley 1966; W. Osborne unpub. data.). Tadpoles develop within the egg capsule and hatching occurs when high ground-water levels after rain cause the nest to become flooded (Osborne 1990a). Hatching occurs at 4 to 6 months (W. Osborne unpub. data.) and the tadpole development period is 6 to 8 months (Pengilley 1966, 1973; W. Osborne unpub. data.). Metamorphsis occurs between Dec. and early Feb. (Pengilley 1966, 1973; W. Osborne unpub. data.). FeedingThe diet of subadults and adults consists largely of small ants and, to a lesser extent, other invertebrates (Osborne 1990a). Food intake is greatly reduced during winter, with many individuals apparently not feeding (Osborne 1990a).Invasive speciesOsborne (1990b) noted that invasive exotic plant species occurred at a number of breeding sites in the Fiery Range and n. Brindabella Range. The two most prominent species in terms of their potential to cover large areas of breeding habitat were Blackberry Rubus fruticosus and Monkey Musk, Mimulus moschatus. Blackberry has the potential to completely smother and shade breeding habitat rendering it unsuitable for frogs. In contrast, Monkey Musk, a short, broad-leafed herb, forms dense patches in seepages where it often occurs with a similar sized native species Gratiola latifolia. Breeding was observed in areas with Monkey Musk and it is not known if it has any detrimental affect. [Osborne 1990a]Excavation by Feral Pigs and trampling by Horses have also been identified as potentially threatening processes for the species (Osborne 1990a; W. Osborne pers. comm.). MovementsOsborne (1988) conducted a two year program of pitfall trapping at Ginini Flats in the ACT. Ginini Flats is a large Sphagnum bog surrounded by dry Bossiaea foliosa heath and subalpine woodland. The results of the study indicated that at the end of the breeding season adult male and female Corroboree Frogs undertake season movement away from the bog, upslope into surrounding heath and woodland. The dispersal distances travelled at this time can be up to 300m.[Osborne 1990]

Pseudophryne pengilleyi is one of a number of Australian alpine amphibian species, including Litoria verreauxii alpina, Pseudophryne corroboree and Philoria frosti, which have experienced pronounced population declines for unknown reasons (Osborne et al. 1999). There is no single aspect of the field biology of these species which stands out as a feature in common that may help explain the declines (Osborne et al. 1999). Pseudophryne pengilleyi is still widespread and abundant at lower altitudes, but there are few remaining substantial populations of the other three species (Osborne et al. 1999). Osborne et al. (1999) reviewed some of the possible factors contributing to population declines at high altitudes including long term weather patterns and pathogens such as the Chytrid fungus (Berger et al. 1999). Chytrid fungus has recently been detected in some museum specimens of P. pengilleyi by R. Speare (W. Osborne pers. comm.). Management of Buccleuch SF in the n. Fiery Range and exotic conifer plantations which cover a considerable extent of the n. part of the region is also a concern (Osborne 1990a).

The northern corroboree frog reaches sexual maturity at three years of age and breeds over a three week period at some point between January and March (4). Between 16 and 40 small eggs are laid which hatch four to six months later, following rains heavy enough to raise ground-water levels and flood the nest. The newly hatched tadpoles are washed into small pools of water where they remain for the next six to eight months. The metamorphosis from tadpole to adult frog takes place between December and early February (1). Adults consume mainly ants. They rarely survive long enough to breed more than once and few of their offspring survive (6).

Much of the habitat occupied by northern corroboree frogs is within reserves, providing protection for the frogs and their habitat. Research into the behaviour, biology and range of the frog is being undertaken and population monitoring is in place (1).

Differing in appearance only slightly from the corroboree frog (Pseudophryne corroboree), the northern corroboree frog has the same distinctive bright yellow and black striped back. However, the stripes are a greener shade of yellow and are also a little narrower (6). The underside has white, black and yellow-green blotches (2). Females are larger than males and, unusually, neither sex has webbed toes. In some areas, 'corroboree' is an aboriginal word for a gathering or meeting – where traditionally the attendees are adorned with yellow markings not unlike those of this rare frog (5).

During the summer breeding season, the northern corroboree frog is found in sphagnum bogs and wet heath in sub-alpine areas, but in dense patches of herbs at lower elevations. Through the winter it is found in the leaf litter of forests, sub-alpine woodlands and tall heaths near the breeding area (1) (2).

Endemic to Australia, the northern corroboree frog is found in the northern Australian Alps of New South Wales and in the Australian Capital Territory (1).

The northern corroboree frog is classified as Endangered (EN B1ab(ii,iv,v) + 2ab(ii,iv,v)) on the IUCN Red List 2004 (1), as Vulnerable on Schedule 2 of the Threatened Species Conservation Act (3) and as Vulnerable under the federal government's Environmental Protection and Biodiversity Conservation (EPBC) Act (4).

The decline of the northern corroboree frog has been monitored with despair, as the exact cause of the drop in numbers, and that of other Australian amphibian species, is not known. Factors thought to be contributing include the detrimental effects of introduced plants such as blackberry (Rubus fruticosus) and monkey musk (Mimulus moschatus), which smother the breeding sites of the frog, as well as the trampling effects of feral pigs and introduced horses (1). Habitat loss, erosion and human disturbance are also thought to have contributed (3). A pathogen called Chytrid fungus has been detected in museum specimens, and is now the major suspect for the cause of the decline (1) (4).

The northern corroboree frog (Pseudophryne pengilleyi) is a species of Australian ground frog, native to southeastern Australia.