Green and Golden Bell Frog
Encyclopedia
The Green and Golden Bell Frog (Litoria aurea), also named the Green Bell Frog, Green and Golden Swamp Frog and Green Frog, is a 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 11 centimetres (4.3 in) 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. Unlike most frogs, they are active at day although this is mostly to tan 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 nine 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 frequent 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 vulnerable. Its numbers have continued to fall and are threatened by habitat loss and degradation, pollution, introduced species, and parasites and pathogens, including 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, the frog remains abundant in New Zealand
and several other Pacific Islands, where it has been introduced.
in his 1975 book Reptiles & Amphibians of Australia. Before this, its common names were "Golden Frog" and "Golden Treefrog". The Green and Golden Bell Frog have 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 Rana genus, 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 Lesson
in 1827. It has changed classification 20 times; it was first named Litoria aurea in 1844 by Günther
, and changed another nine times before being named again as Litoria aurea. The specific epithet aurea derived from the Latin
aureus for 'golden'. The species is now classified within the Litoria aurea complex, a closely related group of frogs in the Litoria
genus. 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 (Litoria aurea), Growling Grass Frog
(Litoria raniformis), Yellow-spotted Bell Frog (Litoria castanea), Dahl's Aquatic Frog
(Litoria dahlii), Spotted-thighed Frog (Litoria cyclorhyncha
) and the Motorbike Frog (Litoria moorei). The ranges of L. raniformis and L. 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 up until 1972, L. 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 Litoria aurea located near Ulong, New South Wales, be a separate species Litoria aurea ulongae, but this was not accepted.
Litorea aurea is equally and most closely related to Litoria castanes and Litoria ranaformis. A micro-complement fixation technique using serum albumin
s has indicated that the species closest to Litoria aurea is Litoria ranifomis. Albumin immunological distance data suggest no differentiation between Litoria ranifomis and Litoria castanea, and that 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 that 4 of 19 protein systems had variation and only two had differentiation. Scientists believe that the different species can still hybridise as their distribution areas stll overlap, and both raniformis and aurea have been seen sharing ponds in the Gippsland
area of Victoria
. However, there has been little evidence of hybridisation actually occurring. Although there have been reports of frogs of mixed appearance in Gippsland, analysis of proteins and serums of the frogs showed two distinct species. Samples in other area of distribution have shown no evidence of hybridisation in spite of co-habitation.
, to East Gippsland
, in Victoria
, and west to Bathurst
, Tumut
and the Australian Capital Territory
.
The Bell Frog's current distribution now ranges from Byron Bay, in northern New South Wales, to East Gippsland, in Victoria; populations mostly occurring 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 250 metres (820 ft), except for a population in Captains Flat. A study of populations along coastal New South Wales indicated that many populations were very small, usually of fewer than 20 adults. According to a 1996 study, there are six known populations of more than 300 frogs: two in the Sydney metropolitan area, two in the Shoalhaven
and two in the New South Wales mid-north coast. There are now approximately only 40 sites in total where it is found, most of which are in the Sydney area. It is estimated that the Green and Golden Bell Frog has disappeared from at least 90% of its former range. Some specimens were apparently found in Armidale
, but it turned out to be a misidentification of Litoria castanea. The declines in Victoria have been more modest and mostly in at inland areas where habitats have disappeared.
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. The Green and Golden Bell 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 and it is now common on the part of North Island
north of Rotorua
. In most places it is the only frog species in the vicinity. However there have been reports of a recent decline, 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.
There is no discernible variation in size or appearance in Green and Golden Bell Frogs between different geographic areas. 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.
The Green and Golden Bell Frog is a large, stout frog; adults range from 4.5 to 11 centimetres (1¾ to 4¼ in) in length; typical specimens measure 6 to 8 centimetres (2½–3¼ in). The Green and Golden Bell Frog is therefore one of the largest Australian frogs. Mature male Green and Golden Bell Frogs are generally smaller than mature females, and the colour on their dorsal surface differs greatly to 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 Green and Golden Bell frogs are inactive, colouration may darken almost to black. They can also darken in this way by simply staying in a dark place for a few minutes and the colour can also evolve during the frog's lifetime.
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 dorso-lateral 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 sac
on the throat. 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 pad
s on their thumbs, which are used to grip females during mating. These are coloured brown during the breeding season, but are unconspicuous and paler during the rest of the year. During the breeding season, females develop a blueish hue on their feet, while males' legs turn rusty orange.
As a member of the tree frog family, the Green and Golden Bell Frog spends much time basking in the sun on vegetation, rocks and reeds, usually near water, or hopping around between such places. Unlike most frog species it is often active during the day. When handled, this species secretes a slimy acrid mucus which consists of 17 aurein peptide
s. Thirteen of these show broad-spectrum antibiotic
and anti-cancer activity, which is useful in fighting off harmful microorganism
s. The secretion makes the frog slippery and hard to grip, and is poisonous to some other species of frogs, so it is a useful defensive tool for Green and Golden Bell Frogs. Male Green and Golden Bell Frogs often fight one another if they come within 1 m of each other, frequently leading to injuries.
The Green and Golden Bell Frog has been detected in a wide range of habitats. It is generally associated with coastal swamps, wetlands, marsh
es, dams, ditches, small rivers, woodland
, and forest
; but populations have also been found at former industrial sites (for instance, the Brickpit). It has even been found in human vessels such as bathtubs. The requirements of its habitat have been difficult to determine, for it has been found in a wide range of water bodies except fast-flowing streams. It is most typically found in short-lived freshwater ponds that are still, shallow, unshaded and unpolluted; and it tends to avoid waters that contain predatory fish
, whether native or introduced. However, it is most often found in areas that have been affected by human habitation. The frog prefers water bodies that support emergent vegetation such as reeds and bullrushes for basking, and winter habitats consist of available shelters around the breeding site, which can be vegetation, rocks, rubbish or human debris and discarded building materials. Grassy habitats are usually close at hand to provide suitable terrestrial
feeding grounds. It prefers waterways with a substrate of sand, rock or clay, and can tolerate a wide range of water turbidities, pH
, oxygen and temperature, although these can hamper physical growth. Although its legs provide much grip, the frog does not choose to climb trees or live up them to any significant extent. They spend most of their time within 10 cm of the ground and rarely venture more than a metre above the ground. The Green and Golden Bell Frog also has the ability to sit still for several minutes.
The Green and Golden Bell Frog can travel far in a single day or night; distances of 1–1.5 km have been recorded. Tagging experiments have shown that some can move up to 3 km and in total and that some travel several kilometres from the closest breeding habitat. However, there is evidence that the species tends to return to or remain at an identified site, provided that the habitat stays appropriate for its needs, else it will move away. The Green and Golden Bell Frog also favours areas
with the greatest habitat complexity, and as such, this is a core component of habitat-based strategies to protect the species. In general, the frogs stay within areas of 100–700 m2 The frog is well-equipped for survival on land. They can rehydrate by absorbing moisture through their ventral skin, and evaporative water loss occurs at a very low rate indicative of a watertight skin. Some have been observed up to 400 m from the nearest body of water.
During the winter months, the frog tends to be inactive, staying in one place, whereas it moves around during the warmer months to search for food and mating partners. During winter, the frog does become active for brief periods during warm or wet weather. It has been claimed by some scientists that in cold conditions, the frogs hibernate, based on observations of some being uncovered in a "torpid" state, but this has yet to be proven with rigorous physiological studies. Although the frog is active during the day, this is restricted to leaving its shelter to sunbathe. It tends to not actively feed or forage during the day, hunting insects only if they move into their vicinity.
The Green and Golden Bell Frog's reproduction depends on salinity and water temperature. Salinity affects tadpole
s' development and metamorphosis, and breeding is significantly slowed for ponds that measure 20 °C (68 °F) or below. The Green and Golden Bell Frog tadpoles can tolerate salinity levels of six parts per thousand (ppt) without any apparent effects, while salinity of 8 ppt or higher decreases growth rates and increases mortality rates. On the other hand, salinity levels of at least 1–2 ppt can be beneficial to the Green and Golden Bell Frog because this kills pathogens such as the chytrid fungus. The pH
of the pond is not found to affect the likelihood of the eggs to hatch for values of the pH between 4 and 10.
s such as crickets, larvae, mosquito wrigglers, dragonflies, earthworms, cockroaches, flies and grasshoppers. It is also known to eat freshwater crayfish and slugs. It eats other frogs, even of the same species. It has a strong tendency for cannibalism, and it is frequently to see Green and Golden Bell Frogs in the same enclosure devour each other. Studies and trials in the wild have shown that cannibalism also occurs in the wild.
The tadpoles feed on detritus
, algae
and bacteria
. Tadpoles in a more advanced phase of development may show a preference for vegetable matter but also scavenge or become carnivorous on aquatic life. Captive tadpoles have eaten boiled lettuce and pet food in pellet form. If there is a high density, tadpoles have cannibalised one another.
In captivity the Green and Golden Bell Frog is known to feed on crickets, fruit flies, maggots, silkworms, domestic flies, beetles, mealworms, larvae, slaters, cockroaches, molluscs, plague locusts, spiders, water snails, earthworms and mice. A case of a small tiger snake being eaten has also been reported. Captive frogs have a habit of not responding to stationary food items, which has helped to form the belief that the frog will eat most things that move.
The hunting habits of the frogs change depending on their growth phase and thus physical size. Smaller, still-growing Green and Golden Bell Frogs tend to hunt small insects, especially flying victims, often jumping to catch their prey. Adult frogs appear to show a distinct preference for larger land-based insects and frogs, although they also eat aquatic prey such as tadpoles and other aquatic organisms. Recently metamorphosed individuals have also been seen enter to shallow water
to capture mosquito wrigglers. The relative proportion that various prey make up in the frog's diet is not known. It has been observed in studies of captive frogs that they eat less in cooler periods of the year, and that frogs in the wild ate less during breeding periods. Younger frogs were also seen to forage longer into the warmer months to build up food stocks than fully matured frogs.
Natural predators include wading bird
s such as reef egrets, white-faced heron
s, white ibis
es and swamp harriers
. Other predators include snake
s, skink
s, red fox
es, tortoise
s, eel
s, other fish such as redfin perch and European carp, several varieties of gudgeon and a range of invertebrate
predators such as the large brown mantis. Predation on adult frogs has been recorded for the Red-bellied Black Snake
, Tiger snake, laughing kookaburra
, Sacred kingfisher
and it is believed that wading birds and other snakes such as the Green tree snake
and the Copperhead snake are predators of the frog. The relative magnitude of the various predatorial threats to the frog and its tadpoles is not known. Before the frog became rare, and when subsistence lifestyles were more common, it was hunted and eaten by Australian Aborigines
. It was also used in dissection demonstrations in biology classes, and caught by humans for feeding pet reptiles when it was more common.
Males appear to reach maturity at around 45–50 mm, at between 9 and 12 months, and at this size begin to develop a grey to brownish yellow wash beneath the chin. This indicates the development of a vocal sac and thus an ability to commence calling behaviour. Observations show that females reach sexual maturity at two years as those smaller than 65 mm are not seen in amplexus
; this length is not reached until the second season after metamorphosis. The frog is not of a type that only breeds once. Females spawn can shed up to 26% of their weight when spawning, while males have also been seen to lose weight during breeding, because they are doing less eating. The weight lost during the breeding season is typically found to be regained from January to September.
Amplexus between the male and female occurs mainly in water, but sometimes at substantial distances away on dry land. Observations of breeding sites have shown that males linger around the courting area for much longer times, while females mostly stay at other places to find food before meeting the males there. During amplexus, the males grab the females near their armpits after climbing on their backs. In the wild amplexus usually takes 10 210 minutes. Artificially induced amplexus in the laboratory has been observed to last 50 hours, but there have been reports of 5 days. Sometimes amplexus will not result in eggs being laid.
The frogs may move up to 100 m during amplexus before the female lays her eggs. During the laying of the eggs, the pair of frogs remain in amplexus and the male is assumed to fertilise the eggs with his sperm. Males are also seen to paddle their rear legs during this time, which is speculated to accelerate fertilisation. The egg-laying and fertilisation process takes around five minutes. An average of 5,000 eggs are deposited amongst aquatic vegetation in a gelatinous mass; however, a clump of 11,682 has been recorded. The female moves around while depositing, leaving a trail of eggs that sometimes entangles upon itself. Initially, the mass floats, but sinks up to 12 hours after laying, or when disturbed. The eggs are distinct from those of other frog species; they are 2–2.5 mm wide upon deposition and are bicoloured, black at one end and white at the other. They immediately begin to expand, quickly reaching around 4 mm across, before sinking. When first laid they float with the black pointing up, but after sinking, the orientation becomes disordered. Two to five days later, the tadpoles hatch out, although there have been reports of the process taking only a few hours on occasions. The hatching rate varies between 46 and 77%, and peaks at 22 degrees Celsius. Hatching is less likely in acidic waters, although alkaline conditions do not lead to a lower rate compared to neutral conditions. Given the large number of eggs that hatch per female, it is believed that given the scarcity of mature frogs, tadpole survival rates are very low.
Upon hatching, the tadpoles are around 2.5–3 mm in snout-vent length and about 5–6 mm including the tail. Tadpoles in captivity increase exponentially over time in total length; their SVL increases from about 3 to about 9 mm within five weeks and it triples again in the next five weeks. In all there is a growth rate of 0.2 mm per day in the first five weeks. The tadpoles of the Green and Golden Bell Frog are large, reaching 80 millimetres (3.15 in) in length, but size varies greatly and most are much shorter. The body is usually as wide across as it is deep. The fin has a yellow tinge and is considerably arched. The musculature is moderate and tapers to a fine point as does the fin. The body wall is translucent yellow with darker areas over the abdomen. Just before its limbs form, the tadpole begins to develop the greenish colouration of the adult. Tadpoles usually swim within 30 cm of the water surface, or remain stationary at the bottom. They often move together in groups akin to schools of fish.
Towards the end of the tadpole phase, hind legs appear, followed by front limbs, and the phase ends when the front limbs are developed. This normally occurs between October and April due to the breeding season, but tadpoles been observed in the wild throughout the year, suggesting that some tadpoles overwinter; this has been seen to occur for captive tadpoles. The length of the tadpole stage, in the wild and in captivity, is usually between 10 and 12 weeks but can range from 5 weeks to a year. The slower-growing tadpoles usually progress during winter, as there is a correlation between growth rates and higher temperature. There was insignificant variation in growth rate across pH values of 4, 7 and 9. In the first four weeks, there was no significant dependence of the growth rate across the 18–26 degrees range, but from this point on, growth was significantly hindered at 18 deg. At the beginning of the metamorphling stage, all limbs are present and developed, along with a tail. During this phase, the tail is resorbed, and the only other visible change is the spiracle closing. Metamorphlings typically have a SVL of 22–28 mm, and will complete metamorphosis between 2 and 11 months, depending on the temperature of the water and available food. The process is slowed at low temperature, but generally takes between three to eight days after the tadpole stage is complete. Breeding occurs in a significantly higher proportion of sites where no predatory fish are present, and water bodies are ephemeral rather than permanent. Populations in Victoria, however, have been recorded as breeding in permanent ponds as readily as they do in ephemeral ponds.
Metamorphs resemble the adults and average about 2.6 centimetres (1 in) in length. Recently metamorphosed frogs have been observed to rapidly leave the breeding site, especially when foraging habitat is nearby, and less so if food is not available away from the area. The tendency to migrate is often attributed to cannibalism practised by larger frogs on those that are still developing. After metamorphosis is complete, the frog is around the same length. The juveniles initially grow rapidly, reaching 45 mm within two months, 50–60 mm within half a year, before growth slows. months, and increase in length more slowly after that. Once sexual maturity is reached, the frogs' physical growth is very slow.
Metamorphlings weigh about 2 g while the largest adults can reach 50 g. Individual frogs can vary substantially in body weight due to changes in the amount of stored fat, recent eating and egg formation. While it is known to live 10–15 years in captivity, the frog's lifespan in the wild is not well understood.
There are many factors thought to be responsible for the dramatic decline of this species in Australia: these include habitat fragmentation, erosion and sedimentation of soil, insecticides and fertilisers contaminating water systems, the introduction of predatory fish and alteration of drainage regimes. Population declines are closely related to the introduction of the Eastern Mosquitofish
(Gambusia holbrooki), a species native to North America that was introduced in order to control mosquito
larvae. Laboratory studies have demonstrated that the eggs and tadpoles of the Green and Golden Bell Frog are extremely susceptible to predation by this fish, and in 77 of the 93 sites in New South Wales where the Green and Golden Bell Frog was known to have disappeared before 1990, Eastern Mosquitofish was found to be present. The frogs have been known to inhabit waters containing the fish, but breeding is rarely successful there, pointing to the fish's voracious eating of eggs and tadpoles. The fish are not yet present in eastern Victoria, where Green and Golden Bell Frog numbers have remained solid, but it is anticipated that the fish will spread to rivers there, possibly inflicting heavy losses on the frogs.
Other factors thought to affect this species include predation by introduced mammal
s such as cat
s and fox
es, changes to water quality at breeding sites, herbicide
use, and loss of habitat through the destruction of wetland
s. The amphibian chytrid
fungus appears to have led to at least some of the decline in numbers, but the relative importance of the various factors is unclear. It is also speculated that the frogs have become more susceptible to chytrid rather than the fungus being more common. The genetic pool of the frogs has been found to be relatively small, something attributed to habitat destruction, which has confined the smaller groups of frogs to isolated pockets and increased the incidence of in-breeding. This has led to proposals for frog populations to be mixed by human intervention in an attempt to reduce negative genetic effects and boost survival rates.
There has also been speculation that the cannibalism of the frog has caused its decline in some areas, because the smaller tadpoles that it eats can be toxic. Other postulated causes of the decline include increased ultra-violet radiation due to the hole in the ozone layer
, global warming
and increased drought. The first theory was tested and the results were inconclusive. Global warming is not thought to be a credible cause as the extremities of the frog's range has not changed, while declines in population have occurred in both dry and wetter areas.
The Green and Golden Bell Frog has been the subject of much research and monitoring, important to improving its conservation. Research focuses on the development of management measures to keep the introduced mosquitofish under control. These include poisoning the fish, but the waterways are large and trials have given mixed results. Predators of the mosquitofish have also been tried. Other strategies may allow for the development and improvement of suitable habitat, and to increase the reproductive success of the species. Parallel to these measures, community awareness programmes have also been proposed. One difficulty in protecting the frog is that only 20% of the known populations in New South Wales since 1990 occur in conservation parks. Of the eight populations that occur in conservation parks, only five are wholly located within them and one of these is non-breeding. There have been calls for legislation to be introduced to stop habitat degradation on private land to prevent detrimental effects to the frogs. Many proposed developments have been subjected to legal action to protect the habitat, and some communities have started "Friends of the Green and Golden Bell Frog" action groups. As public awareness has increased, documentary and news segments on the deteriorating situation have become more frequent and references to the frog in environmental logos and artworks have increased. The effort to increase public consciousness of the Green and Golden Bell Frog has also been aided by the fact that its colours are the same as the national colours. Restrictions on logging close to areas inhabited by the frogs have been put in place. As Green and Golden Bell Frogs are mostly observed in environments disturbed by humans, targeted environmental interference is seen as a possible means of enhancing habitats.
In 1998 a captive breeding program was set up by the herpetofauna staff at Taronga Zoo
in Sydney
, sponsored by the ASX Frog Focus. The purpose of the program was to help preserve declining populations of Green and Golden Bell Frogs in the Sydney region. It involved the captive breeding of wild frogs and releasing large numbers of tadpoles back into the wild, habitat restoration and post-release monitoring. The program was initially titled Frog Focus Botany as Botany
was the original focus site. Thousands of tadpoles were released into a site in Sir Joseph Banks Reserve and post-release monitoring was done by the local community. It was also the first time that school students had been involved with endangered species monitoring. The program has since branched off into several other areas. Between 1998 and 2004, tadpoles were released into specially designed ponds and dams on Long Reef Golf Course at Collaroy
in northern Sydney, with little success. Although Green and Golden Bell Frogs had previously been located in the area, the population had since been lost. Mature male Bell Frogs are occasionally found there; however, a permanent breeding population is yet to be established. An attempted reintroduction at Marrickville
in inner-Sydney has failed due to chytrid.
Tree frog
Hylidae is a wide-ranging family of frogs commonly referred to as "tree frogs and their allies". However, the hylids include a diversity of frog species, many of which do not live in trees, but are terrestrial or semi-aquatic.-Characteristics:...
native to eastern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. 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 11 centimetres (4.3 in) 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. Unlike most frogs, they are active at day although this is mostly to tan 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 nine 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
Sydney
Sydney is the most populous city in Australia and the state capital of New South Wales. Sydney is located on Australia's south-east coast of the Tasman Sea. As of June 2010, the greater metropolitan area had an approximate population of 4.6 million people...
region, inhabit areas of frequent 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 vulnerable. Its numbers have continued to fall and are threatened by habitat loss and degradation, pollution, introduced species, and parasites and pathogens, including chytrid
Chytridiomycota
Chytridiomycota is a division of the Fungi kingdom. The name is derived from the Greek chytridion, meaning "little pot", describing the structure containing unreleased spores. In older classifications, chytrids were placed in the Class Phycomycetes under the subdivision Myxomycophyta of the...
(Batrachochytrium dendrobatidis
Batrachochytrium dendrobatidis
Batrachochytrium dendrobatidis is a chytrid fungus that causes the disease chytridiomycosis. In the decade after it was first discovered in amphibians in 1998, the disease devastated amphibian populations around the world, in a global decline towards multiple extinctions, part of the Holocene...
). As most of the remaining populations live on private land, the logistics of the conservation effort can be complicated. Despite the situation in Australia, the frog remains abundant in New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
and several other Pacific Islands, where it has been introduced.
Taxonomy
The common name, "Green and Golden Bell Frog", was first adopted by Harold CoggerHarold Cogger
Harold George Cogger is an Australian herpetologist. He was curator of reptiles and amphibians at the Australian Museum from 1960-1975, and Deputy Director from 1976-1995...
in his 1975 book Reptiles & Amphibians of Australia. Before this, its common names were "Golden Frog" and "Golden Treefrog". The Green and Golden Bell Frog have many physical and behavioural characteristics representative of ranids
True frog
The true frogs, family Ranidae, have the widest distribution of any frog family. They are abundant throughout most of the world, occurring on most continents except Antarctica...
; hence its original classification as Rana
Rana (genus)
Rana is a genus of frogs. Species include such archetypal pond frogs as the common frog of Europe, brown frogs, and the New and Old World true frogs, including the various species of leopard frogs and the American bullfrog. Members of this genus are found through much of Eurasia, North America,...
. 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 Rana genus, 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
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
structural formations of the Green and Golden Bell Frog are closest to those of species in the family Hylidae; it was therefore reclassified.
René-Primevère Lesson
René Primevère Lesson was a French surgeon, naturalist, ornithologist, and herpetologist.Lesson was born at Rochefort, and at the age of sixteen he entered the Naval Medical School there...
in 1827. It has changed classification 20 times; it was first named Litoria aurea in 1844 by Günther
Albert C. L. G. Günther
Albert Karl Ludwig Gotthilf Günther FRS, also Albert Charles Lewis Gotthilf Günther , was a German-born British zoologist, ichthyologist, and herpetologist....
, and changed another nine times before being named again as Litoria aurea. The specific epithet aurea derived from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
aureus for 'golden'. The species is now classified within the Litoria aurea complex, a closely related group of frogs in the Litoria
Litoria
Litoria is a genus of Hylidae tree frogs native to Australia, the Bismarck Archipelago, the Solomon Islands, New Guinea, the Lesser Sunda Islands, the Moluccan Islands, and Timor. They are sometimes collectively referred to as Australasian treefrogs...
genus. This complex is scattered throughout Australia: three species occur in south-east Australia, one in northern Australia, and two in Southwest Australia
Southwest Australia
Southwest Australia is a biodiversity hotspot that includes the Mediterranean forests, woodlands, and scrub ecoregions of Western Australia. The region has a wet-winter, dry-summer Mediterranean climate, one of five such regions in the world...
. The complex consists of the Green and Golden Bell Frog (Litoria aurea), Growling Grass Frog
Growling Grass Frog
The Growling Grass Frog , also commonly known as the Southern Bell Frog, Warty Swamp Frog and erroneously as the Green Frog is a species of ground dwelling tree frog is native to South eastern Australia; ranging from southern South Australia along the Murray River though Victoria to New South...
(Litoria raniformis), Yellow-spotted Bell Frog (Litoria castanea), Dahl's Aquatic Frog
Dahl's Aquatic Frog
The Dahl's Aquatic Frog is a species of frog in the Hylidae family. It is endemic to Australia.Its natural habitats are dry savanna, subtropical or tropical dry lowland grassland, freshwater lakes, intermittent...
(Litoria dahlii), Spotted-thighed Frog (Litoria cyclorhyncha
Litoria cyclorhyncha
Litoria cyclorhyncha is a Western Australian tree frog species in the Hylidae family.The frog is similar in appearance to a cogenor, Litoria moorei, bearing dark green or brownish patches with bronze or gold highlights on its back; this species can be differentiated by the numerous yellowish spots...
) and the Motorbike Frog (Litoria moorei). The ranges of L. raniformis and L. 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 up until 1972, L. 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 Litoria aurea located near Ulong, New South Wales, be a separate species Litoria aurea ulongae, but this was not accepted.
Litorea aurea is equally and most closely related to Litoria castanes and Litoria ranaformis. A micro-complement fixation technique using serum albumin
Serum albumin
Serum albumin, often referred to simply as albumin is a protein that in humans is encoded by the ALB gene.Serum albumin is the most abundant plasma protein in mammals. Albumin is essential for maintaining the osmotic pressure needed for proper distribution of body fluids between intravascular...
s has indicated that the species closest to Litoria aurea is Litoria ranifomis. Albumin immunological distance data suggest no differentiation between Litoria ranifomis and Litoria castanea, and that 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 that 4 of 19 protein systems had variation and only two had differentiation. Scientists believe that the different species can still hybridise as their distribution areas stll overlap, and both raniformis and aurea have been seen sharing ponds in the Gippsland
Gippsland
Gippsland is a large rural region in Victoria, Australia. It begins immediately east of the suburbs of Melbourne and stretches to the New South Wales border, lying between the Great Dividing Range to the north and Bass Strait to the south...
area of Victoria
Victoria (Australia)
Victoria is the second most populous state in Australia. Geographically the smallest mainland state, Victoria is bordered by New South Wales, South Australia, and Tasmania on Boundary Islet to the north, west and south respectively....
. However, there has been little evidence of hybridisation actually occurring. Although there have been reports of frogs of mixed appearance in Gippsland, analysis of proteins and serums of the frogs showed two distinct species. Samples in other area of distribution have shown no evidence of hybridisation in spite of co-habitation.
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 WalesNew South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...
, to East Gippsland
East Gippsland
East Gippsland is the eastern region of Gippsland, Australia covering 31,740 square kilometres of Victoria. It has a population of 80,114....
, in Victoria
Victoria (Australia)
Victoria is the second most populous state in Australia. Geographically the smallest mainland state, Victoria is bordered by New South Wales, South Australia, and Tasmania on Boundary Islet to the north, west and south respectively....
, and west to Bathurst
Bathurst, New South Wales
-CBD and suburbs:Bathurst's CBD is located on William, George, Howick, Russell, and Durham Streets. The CBD is approximately 25 hectares and surrounds two city blocks. Within this block layout is banking, government services, shopping centres, retail shops, a park* and monuments...
, Tumut
Tumut, New South Wales
Tumut is a town in the Riverina region of New South Wales, Australia, situated on the banks of the Tumut River. Tumut is at the foothills of the Snowy Mountains and is referred to as the gateway to the Snowy Mountains Scheme...
and the Australian Capital Territory
Australian Capital Territory
The Australian Capital Territory, often abbreviated ACT, is the capital territory of the Commonwealth of Australia and is the smallest self-governing internal territory...
.
The Bell Frog's current distribution now ranges from Byron Bay, in northern New South Wales, to East Gippsland, in Victoria; populations mostly occurring 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 250 metres (820 ft), except for a population in Captains Flat. A study of populations along coastal New South Wales indicated that many populations were very small, usually of fewer than 20 adults. According to a 1996 study, there are six known populations of more than 300 frogs: two in the Sydney metropolitan area, two in the Shoalhaven
Shoalhaven
The City of Shoalhaven is a Local Government Area in south-eastern New South Wales , Australia, two hours south of Sydney. It is more or less conterminous with an area referred to as The Shoalhaven. It is on the Pacific Ocean and the Princes Highway and is the terminus of the South Coast line...
and two in the New South Wales mid-north coast. There are now approximately only 40 sites in total where it is found, most of which are in the Sydney area. It is estimated that the Green and Golden Bell Frog has disappeared from at least 90% of its former range. Some specimens were apparently found in Armidale
Armidale, New South Wales
Armidale is a city in the Northern Tablelands, New South Wales, Australia. Armidale Dumaresq Shire had a population of 19,485 people according to the 2006 census. It is the administrative centre for the Northern Tablelands region...
, but it turned out to be a misidentification of Litoria castanea. The declines in Victoria have been more modest and mostly in at inland areas where habitats have disappeared.
The Green and Golden Bell Frog survives in some areas of Sydney
Sydney
Sydney is the most populous city in Australia and the state capital of New South Wales. Sydney is located on Australia's south-east coast of the Tasman Sea. As of June 2010, the greater metropolitan area had an approximate population of 4.6 million people...
, such as the Brickpit at Sydney Olympic Park
Sydney Olympic Park
Sydney Olympic Park is a suburb in western Sydney, in the state of New South Wales, Australia. Sydney Olympic Park is located 16 kilometres west of the Sydney central business district, in the local government area of Auburn Council....
(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. The Green and Golden Bell 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
Kooragang Island
Kooragang Island is located in the Hunter River of New South Wales, Australia and is the site of a deep water port for the export of coal. In 2007, 84.8 million metric tons of coal were exported from the port, making it one of the busiest in the world...
and Broughton Islands
Broughton Island, New South Wales
Broughton Island is an island north east of Port Stephens, New South Wales, Australia. It was seen by James Cook commanding HM Bark Endeavour on 11 May 1770: he mistook it for a headland and called it Black Head. After its insularity was discovered, it was re-named Broughton Islands, and so appears...
off Port Stephens
Port Stephens
Port Stephens is a large natural harbour located about north-east of Sydney in New South Wales, Australia. It lies wholly within the Port Stephens Local Government Area although its northern shoreline forms the boundary between the Port Stephens and Great Lakes LGAs...
and Bowen Island at Jervis Bay
Jervis Bay Territory
The Jervis Bay Territory is a territory of the Commonwealth of Australia. It was surrendered by the state of New South Wales to the Commonwealth Government in 1915 so that the Federal capital at Canberra would have "access to the sea"....
. It was introduced to New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
in the 1860s and it is now common on the part of North Island
North Island
The North Island is one of the two main islands of New Zealand, separated from the much less populous South Island by Cook Strait. The island is in area, making it the world's 14th-largest island...
north of Rotorua
Rotorua
Rotorua is a city on the southern shores of the lake of the same name, in the Bay of Plenty region of the North Island of New Zealand. The city is the seat of the Rotorua District, a territorial authority encompassing the city and several other nearby towns...
. In most places it is the only frog species in the vicinity. However there have been reports of a recent decline, suspected to be due to predatory fish. It was also introduced to the Pacific island countries of New Caledonia
New Caledonia
New Caledonia is a special collectivity of France located in the southwest Pacific Ocean, east of Australia and about from Metropolitan France. The archipelago, part of the Melanesia subregion, includes the main island of Grande Terre, the Loyalty Islands, the Belep archipelago, the Isle of...
and Vanuatu
Vanuatu
Vanuatu , officially the Republic of Vanuatu , is an island nation located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is some east of northern Australia, northeast of New Caledonia, west of Fiji, and southeast of the Solomon Islands, near New Guinea.Vanuatu was...
in the 19th century, and has since become common there.
There is no discernible variation in size or appearance in Green and Golden Bell Frogs between different geographic areas. 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.
Description
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
Eardrum
The eardrum, or tympanic membrane, is a thin membrane that separates the external ear from the middle ear in humans and other tetrapods. Its function is to transmit sound from the air to the ossicles inside the middle ear. The malleus bone bridges the gap between the eardrum and the other ossicles...
to the groin. This stripe rises to form a dorso-lateral 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 sac
Vocal sac
The vocal sac is the flexible membrane of skin possessed by most male frogs. The purpose of the vocal sac is usually as an amplification of their mating or advertisement call...
on the throat. 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 pad
Nuptial pad
A nuptial pad is a secondary sex characteristic present on some mature male frogs and salamanders. Triggered by androgen hormones, this breeding gland appears as a spiked epithelial swelling on the forearm and prepollex that aids with grip, used primarily by males to grasp females during amplexus...
s on their thumbs, which are used to grip females during mating. These are coloured brown during the breeding season, but are unconspicuous and paler during the rest of the year. During the breeding season, females develop a blueish hue on their feet, while males' legs turn rusty orange.
Ecology and behaviour
Peptide
Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
s. Thirteen of these show broad-spectrum antibiotic
Broad-spectrum antibiotic
The term broad-spectrum antibiotic refers to an antibiotic that acts against a wide range of disease-causing bacteria. A broad-spectrum antibiotic acts against both Gram-positive and Gram-negative bacteria, in contrast to a narrow-spectrum antibiotic, which is effective against specific families of...
and anti-cancer activity, which is useful in fighting off harmful microorganism
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...
s. The secretion makes the frog slippery and hard to grip, and is poisonous to some other species of frogs, so it is a useful defensive tool for Green and Golden Bell Frogs. Male Green and Golden Bell Frogs often fight one another if they come within 1 m of each other, frequently leading to injuries.
The Green and Golden Bell Frog has been detected in a wide range of habitats. It is generally associated with coastal swamps, wetlands, marsh
Marsh
In geography, a marsh, or morass, is a type of wetland that is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss....
es, dams, ditches, small rivers, woodland
Woodland
Ecologically, a woodland is a low-density forest forming open habitats with plenty of sunlight and limited shade. Woodlands may support an understory of shrubs and herbaceous plants including grasses. Woodland may form a transition to shrubland under drier conditions or during early stages of...
, and forest
Forest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
; but populations have also been found at former industrial sites (for instance, the Brickpit). It has even been found in human vessels such as bathtubs. The requirements of its habitat have been difficult to determine, for it has been found in a wide range of water bodies except fast-flowing streams. It is most typically found in short-lived freshwater ponds that are still, shallow, unshaded and unpolluted; and it tends to avoid waters that contain predatory fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, whether native or introduced. However, it is most often found in areas that have been affected by human habitation. The frog prefers water bodies that support emergent vegetation such as reeds and bullrushes for basking, and winter habitats consist of available shelters around the breeding site, which can be vegetation, rocks, rubbish or human debris and discarded building materials. Grassy habitats are usually close at hand to provide suitable terrestrial
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
feeding grounds. It prefers waterways with a substrate of sand, rock or clay, and can tolerate a wide range of water turbidities, pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
, oxygen and temperature, although these can hamper physical growth. Although its legs provide much grip, the frog does not choose to climb trees or live up them to any significant extent. They spend most of their time within 10 cm of the ground and rarely venture more than a metre above the ground. The Green and Golden Bell Frog also has the ability to sit still for several minutes.
The Green and Golden Bell Frog can travel far in a single day or night; distances of 1–1.5 km have been recorded. Tagging experiments have shown that some can move up to 3 km and in total and that some travel several kilometres from the closest breeding habitat. However, there is evidence that the species tends to return to or remain at an identified site, provided that the habitat stays appropriate for its needs, else it will move away. The Green and Golden Bell Frog also favours areas
with the greatest habitat complexity, and as such, this is a core component of habitat-based strategies to protect the species. In general, the frogs stay within areas of 100–700 m2 The frog is well-equipped for survival on land. They can rehydrate by absorbing moisture through their ventral skin, and evaporative water loss occurs at a very low rate indicative of a watertight skin. Some have been observed up to 400 m from the nearest body of water.
During the winter months, the frog tends to be inactive, staying in one place, whereas it moves around during the warmer months to search for food and mating partners. During winter, the frog does become active for brief periods during warm or wet weather. It has been claimed by some scientists that in cold conditions, the frogs hibernate, based on observations of some being uncovered in a "torpid" state, but this has yet to be proven with rigorous physiological studies. Although the frog is active during the day, this is restricted to leaving its shelter to sunbathe. It tends to not actively feed or forage during the day, hunting insects only if they move into their vicinity.
The Green and Golden Bell Frog's reproduction depends on salinity and water temperature. Salinity affects tadpole
Tadpole
A tadpole or polliwog is the wholly aquatic larval stage in the life cycle of an amphibian, particularly that of a frog or toad.- Appellation :...
s' development and metamorphosis, and breeding is significantly slowed for ponds that measure 20 °C (68 °F) or below. The Green and Golden Bell Frog tadpoles can tolerate salinity levels of six parts per thousand (ppt) without any apparent effects, while salinity of 8 ppt or higher decreases growth rates and increases mortality rates. On the other hand, salinity levels of at least 1–2 ppt can be beneficial to the Green and Golden Bell Frog because this kills pathogens such as the chytrid fungus. The pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of the pond is not found to affect the likelihood of the eggs to hatch for values of the pH between 4 and 10.
Diet and predators
The voracious adults have a very broad diet, including insectInsect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s such as crickets, larvae, mosquito wrigglers, dragonflies, earthworms, cockroaches, flies and grasshoppers. It is also known to eat freshwater crayfish and slugs. It eats other frogs, even of the same species. It has a strong tendency for cannibalism, and it is frequently to see Green and Golden Bell Frogs in the same enclosure devour each other. Studies and trials in the wild have shown that cannibalism also occurs in the wild.
The tadpoles feed on detritus
Detritus
Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
, algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
and bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
. Tadpoles in a more advanced phase of development may show a preference for vegetable matter but also scavenge or become carnivorous on aquatic life. Captive tadpoles have eaten boiled lettuce and pet food in pellet form. If there is a high density, tadpoles have cannibalised one another.
In captivity the Green and Golden Bell Frog is known to feed on crickets, fruit flies, maggots, silkworms, domestic flies, beetles, mealworms, larvae, slaters, cockroaches, molluscs, plague locusts, spiders, water snails, earthworms and mice. A case of a small tiger snake being eaten has also been reported. Captive frogs have a habit of not responding to stationary food items, which has helped to form the belief that the frog will eat most things that move.
The hunting habits of the frogs change depending on their growth phase and thus physical size. Smaller, still-growing Green and Golden Bell Frogs tend to hunt small insects, especially flying victims, often jumping to catch their prey. Adult frogs appear to show a distinct preference for larger land-based insects and frogs, although they also eat aquatic prey such as tadpoles and other aquatic organisms. Recently metamorphosed individuals have also been seen enter to shallow water
to capture mosquito wrigglers. The relative proportion that various prey make up in the frog's diet is not known. It has been observed in studies of captive frogs that they eat less in cooler periods of the year, and that frogs in the wild ate less during breeding periods. Younger frogs were also seen to forage longer into the warmer months to build up food stocks than fully matured frogs.
Natural predators include wading bird
Wader
Waders, called shorebirds in North America , are members of the order Charadriiformes, excluding the more marine web-footed seabird groups. The latter are the skuas , gulls , terns , skimmers , and auks...
s such as reef egrets, white-faced heron
White-faced Heron
The White-faced Heron, Egretta novaehollandiae, also known as the White-fronted Heron, and incorrectly as the Grey Heron, or Blue Crane, is a common bird throughout most of Australasia, including New Guinea, the islands of Torres Strait, Indonesia, New Zealand, the islands of the Subantarctic, and...
s, white ibis
Australian White Ibis
The Australian White Ibis , is a wading bird of the ibis family Threskiornithidae. It is widespread across much of Australia...
es and swamp harriers
Swamp Harrier
The Swamp Harrier also known as the Marsh Harrier, Australasian Harrier, Kāhu, Swamp-hawk or New Zealand Hawk is a large, slim bird of prey in the family Accipitridae.-Description:...
. Other predators include snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
s, skink
Skink
Skinks are lizards belonging to the family Scincidae. Together with several other lizard families, including Lacertidae , they comprise the superfamily or infraorder Scincomorpha...
s, red fox
Red Fox
The red fox is the largest of the true foxes, as well as being the most geographically spread member of the Carnivora, being distributed across the entire northern hemisphere from the Arctic Circle to North Africa, Central America, and the steppes of Asia...
es, tortoise
Tortoise
Tortoises are a family of land-dwelling reptiles of the order of turtles . Like their marine cousins, the sea turtles, tortoises are shielded from predators by a shell. The top part of the shell is the carapace, the underside is the plastron, and the two are connected by the bridge. The tortoise...
s, eel
Eel
Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...
s, other fish such as redfin perch and European carp, several varieties of gudgeon and a range of invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
predators such as the large brown mantis. Predation on adult frogs has been recorded for the Red-bellied Black Snake
Red-bellied Black Snake
The Red-bellied Black Snake, Pseudechis porphyriacus, is a species of elapid snake native to eastern Australia. Though its venom is capable of causing significant morbidity, it is not generally fatal and less venomous than other deadly Australian snakes. It is common in woodlands, forests and...
, Tiger snake, laughing kookaburra
Laughing Kookaburra
The Laughing Kookaburra, Dacelo novaeguineae, is a carnivorous bird in the kingfisher family Halcyonidae. Native to eastern Australia, it has also been introduced to parts of New Zealand, Tasmania and Western Australia. Male and female adults are similar in plumage, which is predominantly brown and...
, Sacred kingfisher
Sacred Kingfisher
The Sacred Kingfisher is primarily a woodland kingfisher that occurs in mangroves, woodlands, forests, and river valleys of Australia, Lord Howe Is., Norfolk Is., New Guinea, N...
and it is believed that wading birds and other snakes such as the Green tree snake
Green tree snake
Green tree snake may refer to:* Morelia viridis, a.k.a. the green tree python, a non-venomous python species found in New Guinea, various islands in Indonesia, and the Cape York Peninsula in Australia....
and the Copperhead snake are predators of the frog. The relative magnitude of the various predatorial threats to the frog and its tadpoles is not known. Before the frog became rare, and when subsistence lifestyles were more common, it was hunted and eaten by Australian Aborigines
Australian Aborigines
Australian Aborigines , also called Aboriginal Australians, from the latin ab originem , are people who are indigenous to most of the Australian continentthat is, to mainland Australia and the island of Tasmania...
. It was also used in dissection demonstrations in biology classes, and caught by humans for feeding pet reptiles when it was more common.
Reproduction
The Green and Golden Bell Frog breeds in the warmer months from October to March, although some cases have been recorded earlier at the end of winter. Reproduction appears to be influenced by geography. More southerly and highland populations appear to have a shorter window for breeding than their more northerly and lowland counterparts. The latter appear commence breeding earlier and end later than the former group. During the breeding season, males call, usually while floating in the water, but sometimes on vegetation at the side of a pond, mainly at night. They do so with a deep growl that has been described as a four-part "walk-walk sound"—likened to the sound of a motorbike changing gears. It has been found that the males respond to recordings of the call, and that this is why entire groups of males will then call in unison. Males are also more likely to call under certain temperature ranges, 16–23 for water temperature, and 14–25 in the air. Calling is also more likely immediately after rain has occurred.Males appear to reach maturity at around 45–50 mm, at between 9 and 12 months, and at this size begin to develop a grey to brownish yellow wash beneath the chin. This indicates the development of a vocal sac and thus an ability to commence calling behaviour. Observations show that females reach sexual maturity at two years as those smaller than 65 mm are not seen in amplexus
Amplexus
Amplexus is a form of pseudocopulation in which a male amphibian grasps a female with his front legs as part of the mating process...
; this length is not reached until the second season after metamorphosis. The frog is not of a type that only breeds once. Females spawn can shed up to 26% of their weight when spawning, while males have also been seen to lose weight during breeding, because they are doing less eating. The weight lost during the breeding season is typically found to be regained from January to September.
Amplexus between the male and female occurs mainly in water, but sometimes at substantial distances away on dry land. Observations of breeding sites have shown that males linger around the courting area for much longer times, while females mostly stay at other places to find food before meeting the males there. During amplexus, the males grab the females near their armpits after climbing on their backs. In the wild amplexus usually takes 10 210 minutes. Artificially induced amplexus in the laboratory has been observed to last 50 hours, but there have been reports of 5 days. Sometimes amplexus will not result in eggs being laid.
The frogs may move up to 100 m during amplexus before the female lays her eggs. During the laying of the eggs, the pair of frogs remain in amplexus and the male is assumed to fertilise the eggs with his sperm. Males are also seen to paddle their rear legs during this time, which is speculated to accelerate fertilisation. The egg-laying and fertilisation process takes around five minutes. An average of 5,000 eggs are deposited amongst aquatic vegetation in a gelatinous mass; however, a clump of 11,682 has been recorded. The female moves around while depositing, leaving a trail of eggs that sometimes entangles upon itself. Initially, the mass floats, but sinks up to 12 hours after laying, or when disturbed. The eggs are distinct from those of other frog species; they are 2–2.5 mm wide upon deposition and are bicoloured, black at one end and white at the other. They immediately begin to expand, quickly reaching around 4 mm across, before sinking. When first laid they float with the black pointing up, but after sinking, the orientation becomes disordered. Two to five days later, the tadpoles hatch out, although there have been reports of the process taking only a few hours on occasions. The hatching rate varies between 46 and 77%, and peaks at 22 degrees Celsius. Hatching is less likely in acidic waters, although alkaline conditions do not lead to a lower rate compared to neutral conditions. Given the large number of eggs that hatch per female, it is believed that given the scarcity of mature frogs, tadpole survival rates are very low.
Upon hatching, the tadpoles are around 2.5–3 mm in snout-vent length and about 5–6 mm including the tail. Tadpoles in captivity increase exponentially over time in total length; their SVL increases from about 3 to about 9 mm within five weeks and it triples again in the next five weeks. In all there is a growth rate of 0.2 mm per day in the first five weeks. The tadpoles of the Green and Golden Bell Frog are large, reaching 80 millimetres (3.15 in) in length, but size varies greatly and most are much shorter. The body is usually as wide across as it is deep. The fin has a yellow tinge and is considerably arched. The musculature is moderate and tapers to a fine point as does the fin. The body wall is translucent yellow with darker areas over the abdomen. Just before its limbs form, the tadpole begins to develop the greenish colouration of the adult. Tadpoles usually swim within 30 cm of the water surface, or remain stationary at the bottom. They often move together in groups akin to schools of fish.
Towards the end of the tadpole phase, hind legs appear, followed by front limbs, and the phase ends when the front limbs are developed. This normally occurs between October and April due to the breeding season, but tadpoles been observed in the wild throughout the year, suggesting that some tadpoles overwinter; this has been seen to occur for captive tadpoles. The length of the tadpole stage, in the wild and in captivity, is usually between 10 and 12 weeks but can range from 5 weeks to a year. The slower-growing tadpoles usually progress during winter, as there is a correlation between growth rates and higher temperature. There was insignificant variation in growth rate across pH values of 4, 7 and 9. In the first four weeks, there was no significant dependence of the growth rate across the 18–26 degrees range, but from this point on, growth was significantly hindered at 18 deg. At the beginning of the metamorphling stage, all limbs are present and developed, along with a tail. During this phase, the tail is resorbed, and the only other visible change is the spiracle closing. Metamorphlings typically have a SVL of 22–28 mm, and will complete metamorphosis between 2 and 11 months, depending on the temperature of the water and available food. The process is slowed at low temperature, but generally takes between three to eight days after the tadpole stage is complete. Breeding occurs in a significantly higher proportion of sites where no predatory fish are present, and water bodies are ephemeral rather than permanent. Populations in Victoria, however, have been recorded as breeding in permanent ponds as readily as they do in ephemeral ponds.
Metamorphs resemble the adults and average about 2.6 centimetres (1 in) in length. Recently metamorphosed frogs have been observed to rapidly leave the breeding site, especially when foraging habitat is nearby, and less so if food is not available away from the area. The tendency to migrate is often attributed to cannibalism practised by larger frogs on those that are still developing. After metamorphosis is complete, the frog is around the same length. The juveniles initially grow rapidly, reaching 45 mm within two months, 50–60 mm within half a year, before growth slows. months, and increase in length more slowly after that. Once sexual maturity is reached, the frogs' physical growth is very slow.
Metamorphlings weigh about 2 g while the largest adults can reach 50 g. Individual frogs can vary substantially in body weight due to changes in the amount of stored fat, recent eating and egg formation. While it is known to live 10–15 years in captivity, the frog's lifespan in the wild is not well understood.
Conservation status
The numbers of Green and Golden Bell Frogs are estimated to have declined by more than 30% in the past ten years. It is listed as globally and nationally vulnerable, and as endangered under the New South Wales Threatened Species Conservation Act, 1995. Although it is only classified as vulnerable at national level, the National Frog Action Plan classifies the Green and Golden Bell Frog as endangered. In contrast to Australia, the frogs are abundant in New Zealand and classified as feral and unprotected.There are many factors thought to be responsible for the dramatic decline of this species in Australia: these include habitat fragmentation, erosion and sedimentation of soil, insecticides and fertilisers contaminating water systems, the introduction of predatory fish and alteration of drainage regimes. Population declines are closely related to the introduction of the Eastern Mosquitofish
Eastern mosquitofish
The eastern mosquitofish, Gambusia holbrooki, is a species of freshwater fish that is closely related to the western mosquitofish, Gambusia affinis. It is a member of the family Poeciliidae of order Cyprinodontiformes...
(Gambusia holbrooki), a species native to North America that was introduced in order to control mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
larvae. Laboratory studies have demonstrated that the eggs and tadpoles of the Green and Golden Bell Frog are extremely susceptible to predation by this fish, and in 77 of the 93 sites in New South Wales where the Green and Golden Bell Frog was known to have disappeared before 1990, Eastern Mosquitofish was found to be present. The frogs have been known to inhabit waters containing the fish, but breeding is rarely successful there, pointing to the fish's voracious eating of eggs and tadpoles. The fish are not yet present in eastern Victoria, where Green and Golden Bell Frog numbers have remained solid, but it is anticipated that the fish will spread to rivers there, possibly inflicting heavy losses on the frogs.
Other factors thought to affect this species include predation by introduced mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s such as cat
Cat
The cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...
s and fox
Fox
Fox is a common name for many species of omnivorous mammals belonging to the Canidae family. Foxes are small to medium-sized canids , characterized by possessing a long narrow snout, and a bushy tail .Members of about 37 species are referred to as foxes, of which only 12 species actually belong to...
es, changes to water quality at breeding sites, herbicide
Herbicide
Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
use, and loss of habitat through the destruction of wetland
Wetland
A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....
s. The amphibian chytrid
Chytridiomycosis
Chytridiomycosis is an infectious disease of amphibians, caused by the chytrid Batrachochytrium dendrobatidis, a non-hyphal zoosporic fungus. Chytridiomycosis has been linked to dramatic population declines or even extinctions of amphibian species in western North America, Central America, South...
fungus appears to have led to at least some of the decline in numbers, but the relative importance of the various factors is unclear. It is also speculated that the frogs have become more susceptible to chytrid rather than the fungus being more common. The genetic pool of the frogs has been found to be relatively small, something attributed to habitat destruction, which has confined the smaller groups of frogs to isolated pockets and increased the incidence of in-breeding. This has led to proposals for frog populations to be mixed by human intervention in an attempt to reduce negative genetic effects and boost survival rates.
There has also been speculation that the cannibalism of the frog has caused its decline in some areas, because the smaller tadpoles that it eats can be toxic. Other postulated causes of the decline include increased ultra-violet radiation due to the hole in the ozone layer
Ozone depletion
Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere , and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon...
, global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
and increased drought. The first theory was tested and the results were inconclusive. Global warming is not thought to be a credible cause as the extremities of the frog's range has not changed, while declines in population have occurred in both dry and wetter areas.
The Green and Golden Bell Frog has been the subject of much research and monitoring, important to improving its conservation. Research focuses on the development of management measures to keep the introduced mosquitofish under control. These include poisoning the fish, but the waterways are large and trials have given mixed results. Predators of the mosquitofish have also been tried. Other strategies may allow for the development and improvement of suitable habitat, and to increase the reproductive success of the species. Parallel to these measures, community awareness programmes have also been proposed. One difficulty in protecting the frog is that only 20% of the known populations in New South Wales since 1990 occur in conservation parks. Of the eight populations that occur in conservation parks, only five are wholly located within them and one of these is non-breeding. There have been calls for legislation to be introduced to stop habitat degradation on private land to prevent detrimental effects to the frogs. Many proposed developments have been subjected to legal action to protect the habitat, and some communities have started "Friends of the Green and Golden Bell Frog" action groups. As public awareness has increased, documentary and news segments on the deteriorating situation have become more frequent and references to the frog in environmental logos and artworks have increased. The effort to increase public consciousness of the Green and Golden Bell Frog has also been aided by the fact that its colours are the same as the national colours. Restrictions on logging close to areas inhabited by the frogs have been put in place. As Green and Golden Bell Frogs are mostly observed in environments disturbed by humans, targeted environmental interference is seen as a possible means of enhancing habitats.
In 1998 a captive breeding program was set up by the herpetofauna staff at Taronga Zoo
Taronga Zoo
Taronga Zoo is the city zoo of Sydney, New South Wales, Australia. Officially opened on 7 October 1916, it is located on the shores of Sydney Harbour in the suburb of Mosman...
in Sydney
Sydney
Sydney is the most populous city in Australia and the state capital of New South Wales. Sydney is located on Australia's south-east coast of the Tasman Sea. As of June 2010, the greater metropolitan area had an approximate population of 4.6 million people...
, sponsored by the ASX Frog Focus. The purpose of the program was to help preserve declining populations of Green and Golden Bell Frogs in the Sydney region. It involved the captive breeding of wild frogs and releasing large numbers of tadpoles back into the wild, habitat restoration and post-release monitoring. The program was initially titled Frog Focus Botany as Botany
Botany, New South Wales
Botany is a suburb in south-eastern Sydney, in the state of New South Wales, Australia. Botany is located 10 kilometres south of the Sydney central business district and is part of the City of Botany Bay....
was the original focus site. Thousands of tadpoles were released into a site in Sir Joseph Banks Reserve and post-release monitoring was done by the local community. It was also the first time that school students had been involved with endangered species monitoring. The program has since branched off into several other areas. Between 1998 and 2004, tadpoles were released into specially designed ponds and dams on Long Reef Golf Course at Collaroy
Collaroy, New South Wales
Collaroy is a suburb in northern Sydney, in the state of New South Wales, Australia. Collaroy is located 22 kilometres north-east of the Sydney central business district, in the local government area of Warringah Council and part of the Northern Beaches region...
in northern Sydney, with little success. Although Green and Golden Bell Frogs had previously been located in the area, the population had since been lost. Mature male Bell Frogs are occasionally found there; however, a permanent breeding population is yet to be established. An attempted reintroduction at Marrickville
Marrickville, New South Wales
Marrickville, a suburb of Sydney's Inner West is located 7 kilometres south-west of the Sydney central business district in the state of New South Wales, Australia and is the largest suburb in the Marrickville Council local government area...
in inner-Sydney has failed due to chytrid.
External links
- DEH Species Profiles - Litoria aurea
- Frogs Australia Network-frog call available here.
- Frogs of Australia