The green and golden bell frog (Ranoidea aurea), also named the green bell frog, green and golden swamp frog and green frog, is a species of ground-dwelling tree frog native to eastern Australia. Despite its classification and climbing abilities, it does not live in trees and spends almost all of its time close to ground level. It can reach up to in length, making it one of Australia's largest frogs.
Coloured gold and green, the frogs are voracious eaters of insects, but will also eat larger prey, such as worms and mice. They are mainly diurnal, although this is mostly to warm in the sun. They tend to be less active in winter except in warmer or wetter periods, and breed in the warmer months. Males reach maturity after around 9 months, while for the larger females, this does not occur until they are two years old. The frogs can engage in cannibalism, and males frequently attack and injure one another if they infringe on one another's space.
Many populations, particularly in the Sydney region, inhabit areas of infrequent disturbance, such as golf courses, disused industrial land, brick pits, and landfill areas. Though once one of the most common frogs in south-east Australia, the green and golden bell frog has endured major population declines, particularly in highland areas, leading to its current classification as globally endangered. Its numbers have continued to fall and are threatened by habitat loss and degradation, pollution, introduced species, and parasites and pathogens, including the chytrid Batrachochytrium dendrobatidis. As most of the remaining populations live on private land, the logistics of the conservation effort can be complicated. Despite the situation in Australia, some frog populations have survived with more success in New Zealand and several other Pacific islands, where it has been introduced. However, even in these areas the population of green and golden bell has been rapidly declining in the past few decades.
Taxonomy
The common name, "green and golden bell frog", was first adopted by Harold Cogger in his 1975 book Reptiles and Amphibians of Australia. Before this, its common names were "golden frog" and "golden tree frog". The green and golden bell frog has many physical and behavioural characteristics representative of ranids, hence its original classification as Rana. It has a pointy snout, long legs, and almost complete toe webbing; the tympanum is large and distinct; and the overall body shape is similar to many Rana species. Like many frogs in the genus Rana, green and golden bell frogs are mostly aquatic, and only travel over land during periods of rainfall. It was removed from the genus because of anatomical differences with the family Ranidae. The bone and cartilage structural formations of the green and golden bell frog are closest to those of species in the family Hylidae; it was therefore reclassified.
The green and golden bell frog was first described as Rana aurea by René-Primevère Lesson in 1827 and has changed classification many times. The specific epithet aurea derived from the Latin aureus for 'golden'. The species is now classified within the Ranoidea aurea complex, a closely related group of frogs in the genus Ranoidea.Mahony, p. 82. This complex is scattered throughout Australia: three species occur in south-east Australia, one in northern Australia, and two in Southwest Australia. The complex consists of the green and golden bell frog (R. aurea), growling grass frog (R. raniformis), yellow-spotted bell frog (R. castanea), Dahl's aquatic frog (R. dahlii), spotted-thighed frog (R. cyclorhyncha) and the motorbike frog (R. moorei). The ranges of R. raniformis and R. castanea overlap with the green and golden bell frog; this, as well as physical similarities, may make it difficult to distinguish between the species, and until 1972, R. raniformis and the green and golden bell frog were regarded as the same, when electrophoretic studies proved them to be distinct. The tablelands bell frog has not been seen since 1980 and may now be extinct, although the large yellow spots present on its thighs help distinguish it from the green and golden bell frog. The growling grass frog, which is very similar to the green and golden bell frog, can only be readily distinguished by raised bumps on the dorsal surface. It has also been proposed that some populations of R. aurea located near Ulong, New South Wales, be a separate subspecies, R. a. ulongae, but this was not accepted.Pyke and White, p. 568.
Ranoidea aurea is equally and most closely related to R. castanea and R. raniformis. A microcomplement fixation technique using serum albumins has indicated the species closest to R. aurea is R. ranifomis. Albumin immunological distance data suggest no differentiation between the two, and the green and golden bell frog evolutionally separated from the other two species about 1.1 million years ago. A 1995 study of protein variations showed four of 19 protein systems had variation and only two had differentiation. Scientists believe the different species can still hybridise, as their distribution areas still overlap, and both R. raniformis and R. aurea have been seen sharing ponds in the Gippsland area of Victoria. However, little evidence of hybridisation actually occurring has been found. Although there have been reports of frogs of mixed appearance in Gippsland, analysis of proteins and sera of the frogs showed two distinct species. Samples in other area of distribution have shown no evidence of hybridisation in spite of cohabitation.Pyke and White, p. 569.
Distribution
The green and golden bell frog is native to south-eastern Australia. Before its decline in population, its distribution ranged from Brunswick Heads, in northern New South Wales, to East Gippsland, in Victoria,Gillespie G. R. 1996. "Distribution, habitat and conservation status of the Green and Golden Bell Frog Litoria aurea (Lesson, 1829) (Anura: Hylidae) in Victoria." Australian Zoologist 30: 199–207. and west to Bathurst, Tumut and the Australian Capital Territory.Osborne W. S., Littlejohn M. J. and Thomson S. A. 1996. "Former distribution and apparent disappearance of the Litoria aurea complex from the Southern Tablelands of New South Wales and the Australian Capital Territory." Australian Zoologist 30: 190–198.
The bell frog's current distribution now ranges from Byron Bay, in northern New South Wales, to East Gippsland, in Victoria; populations mostly occur along the coast. In New South Wales, it has declined severely in range and abundance since the 1960s, although no similar declines have been reported in Victoria. In New South Wales, it has disappeared from highland areas above , except for a population in Captains Flat. A study of populations along coastal New South Wales indicated many populations were very small, usually of fewer than 20 adults. According to a 1996 study, six populations of more than 300 frogs are known: two in the Sydney metropolitan area, two in the Shoalhaven, and two in the New South Wales mid-north coast.White A. W. and Pyke G. H. 1996. "Distribution and conservation status of the Green and Golden Bell Frog Litoria aurea in New South Wales." Australian Zoologist 30 (2): 177–189. There are now approximately only 40 sites in total where it is found, most of which are in the Sydney area. The green and golden bell frog has disappeared from an estimated 90% of its former range. Some specimens were apparently found in Armidale, but it turned out to be a misidentification of R. castanea.Pyke and White, p. 566. The declines in Victoria have been more modest and mostly in at inland areas where habitats have disappeared.Pyke and White, p. 567.The green and golden bell frog survives in some areas of Sydney, such as the Brickpit at Sydney Olympic Park (the proposed site for the tennis courts for the 2000 Sydney Olympics). When the green and golden bell frog was found there, the tennis courts were built elsewhere, and the population has since been monitored. This frog has become an unofficial mascot for the Homebush Bay area. It has also been introduced to places in Sydney in its natural habitat, without much success.
The green and golden bell frog occurs on three islands off the east coast of Australia: Kooragang and Broughton Islands off Port Stephens, and Bowen Island at Jervis Bay. It was introduced to New Zealand in the 1860s by the Auckland Acclimation Society, and it is now common in the part of the North Island north of Rotorua, and can also be found in South Taranaki and some isolated areas of Southland near Te Anau. In most places, it is the only frog species in the vicinity. However, recent declines have been reported, suspected to be due to predatory fish. It was also introduced to the Pacific island countries of New Caledonia and Vanuatu in the 19th century, and has since become common there.
No discernible variation in size or appearance in green and golden bell frogs between different geographic areas is found. Fluctuations in size and appearance between different populations are outweighed by variations within the populations themselves. Females are more likely to be found away from breeding sites, while the opposite applies for males. Metamorphlings are divided in roughly equal numbers between males and females, while juvenile frogs are observed less often than their mature counterparts, although scientists are not sure whether this is due to lower abundance or increased reclusiveness.Pyke and White, p. 579.
Description
The green and golden bell frog is a large, stout frog; adults range from in length; typical specimens measure . The green and golden bell frog is therefore one of the largest Australian frogs.Egerton, p. 381. Mature males are generally smaller than mature females, and the colour on their dorsal surfaces differ greatly from females. It may be almost completely green, of shades from dark pea-green to bright emerald, green with metallic, brassy, dull copper-brown, or gold markings; or almost completely bronze. Generally, females tend to have more green patches than males. During the cooler months (May–August), when the frogs are inactive, colouration may darken almost to black.Pyke and White, p. 565. They can also darken in this way by simply staying in a dark place for a few minutes, and the colour can also change during the frogs' lifetimes.
A creamy-white or pale yellow stripe, bordered above with gold and below with black, extends from behind the eye, across the typically copper-coloured tympanum to the groin. This stripe rises to form a dorsolateral fold towards the groin. Another stripe of the same colour begins below the eye and continues to the shoulder. The abdomen is cream or white, and has a coarsely granular texture. The legs are green, bronze, or a combination of both, and the inside thigh and groin are blue-green. Mature males develop a yellowish colouration to the vocal sacs on their throats. The tympanum is distinct and ovular in shape, and the species has enlarged toe discs to aid in climbing. As this species is often found in water, the fingers are free from webbing, while the toes are almost completely webbed. When in breeding condition, males develop nuptial pads on their thumbs, which are used to grip females during mating. These are coloured brown during the breeding season, but are inconspicuous and paler during the rest of the year.Draft Recovery Plan for Green and Golden Bell Frog Litoria aurea (Lesson 1829), p. 29. During the breeding season, females develop a blueish hue on their feet, while males' legs turn rusty orange.Pyke and White, p. 570.
Ecology and behaviour