Cane Toad

Family: Bufonidae - True Toads

Order: Anura - Frogs and Toads

Class: Anura

Phylum: Chordata - Vertebrates

Kingdom: Animalia

Red List status: Least Concern

Rhinella marina (Linnaeus, 1758)
Cane toads, amplectant pair. Townsville, Queensland, Australia
Adult length: 100-150 mm, exceptionally to 230 mm

Juvenile length: 30-70 mm

Weight: 250 - 600 g

RANGE

The species' natural range extends from southern Texas in the United States throughout the American Tropics. It has been introduced with varying degrees of success to more northerly regions of the continental United States, parts of the Caribbean, a number of Pacific islands, Indonesia, New Guinea and Australia, a total of at least 41 countries outside its native range.

In Australia the species' range is still expanding; with the toads having colonised much of Queensland and parts of New South Wales and the Northern Territory. By 2006 the species was reported to have reached the border of Western Australia.

Other common names: Marine toad, South American giant toad

DESCRIPTION

Adult: A rather typical large toad. A bony ridge extends from the snout to the eye, producing a high 'eyebrow' ridge. The parotid glands are large and oval. The skin has a distinctly warty texture above; the pale, mottled belly is granular. Body colour is typically grey or olive, though may be brown. Male toads tend to be unpatterned, although the head may be marked with red or other colours in females. The toes are fully webbed; there is no webbing on the fingers. The animal lacks either vomerine or maxillary teeth.

 

Call: A continuous, low-pitched purr sounding somewhat like a motorcycle engine, uttered from the water's edge.

Call recording Jean-Marc Hero

 

Juvenile: Metamorphs broadly resemble adults, but are usually brownish in colour, often with red warts

scattered across the back, and the parotid gland is not prominent. A pale mid-dorsal line may be present.

Profile view of a cane toad showing the prominent, enlarged parotid gland.

Tadpole: A typical 'toadpole', black with a round body and short tail.

Eggs: Laid as strings of black eggs within jelly capsules, draped around vegetation at the bottom of pools.

Cane toad metamorph

 

HABITAT

A cosmopolitan generalist where it occurs, R. marina is found in most habitats with the possible exception of dense forest, apparently having a preference for disturbed sites. In areas where the species has been introduced, it is especially abundant in anthropogenic habitats. There is some evidence that this species exhibits a tolerance for brackish waters, and it has been observed in estuarine environments and mangroves.

Reproductive habitat: The cane toad has been shown to exhibit a preference for laying eggs in shallow pools with gentle slopes and little bankside vegetation, both in parts of its native range and in Australia, and will also breed in slow-flowing rivers and streams. Cane toads breed in both permanent and temporary water bodies, although may prefer the latter. The cane toad is exceptional among anurans in possessing eggs and larvae that are tolerant to low concentrations of salt water.

Elevation: 0 - 3,000 m

 

BEHAVIOUR

Adult cane toads are predominantly nocturnal, and are frequently observed foraging or forming aggregations on roads, in grassland or in other open areas. Adults and juveniles may gather around lights to which insects are attracted. Adult toads are most active following rain, and forage intermittently in 1, 3 or 5 day cycles. This activity may extend well into the dry season, when many other anurans are inactive.

The cane toad is principally terrestrial, although it will enter shallow water and has been observed to swim. In Australia, where the species has been most-studied, the diet consists predominantly of ants and termites, but cane toads have also been found to take other arthropods and, rarely, small vertebrates. The species is unusual among anurans in that it also appears to deliberately include plant matter in its diet in suitable habitats, making it one of very few truly omnivorous frogs. During the day, or in periods of dormancy, cane toads take shelter in any available crevice or burrow, or beneath suitably-sized cover objects.

Larvae feed primarily on algae, although older tadpole cohorts may prey upon eggs and younger tadpoles and, indeed, are the major source of predation on cane toads at this stage in the life cycle. Tadpoles commonly cluster in large aggregations towards the middle of the water column.

Cane toad taking refuge in a diurnal shelter site beneath a brick.

 

BIOLOGY

Breeding biology: Rhinella marina is among the most fecund anurans. In a single breeding episode a female may lay up to 54,000 eggs and may breed several times in a season.

Life cycle: Eggs can hatch in as little as 48 hours of being laid, with tadpoles taking 28-40 days to metamorphose. Sexual maturity is reached at around 18 months of age. Metamorphs remain close to water for 3-4 days before dispersing. In Australia, dispersing juveniles have often been the first colonisers of new habitats, being observed up to a year before colonies become established at a new site.

Lifespan: Animals can live up to five years in the wild.

 

STATUS

Due to its extremely high reproductive potential and resistance to predation, cane toads can rapidly multiply to outnumber other similarly-sized species; in parts of Australia they may be the most abundant vertebrates. Consequently, cane toads are recognised as being an invasive species in a number of areas where they have been introduced, and the World Conservation Union includes the species as one of three amphibians on its "100 Least Wanted" list of exotic species. However, at the same time a number of island populations of R. marina are legally protected, valued for their ability to control pests such as cockroaches in areas naturally lacking abundant insectivores.

Ecology: The cane toad is infamous for its extremely toxic skin secretions, produced in the adult in the parotid glands. The egg and larval stages are also toxic; one species of Australian freshwater snail suffered complete mortality in the presence of toad eggs under experimental conditions. As such, R. marina has comparatively few predators, although the Australian keelback (Tropidonophis mairii) will eat cane toads without ill effects and a number of other Australian predators have developed ways of safely handling the animals. Australia's native turtles appear able to prey on the eggs. At least in Australia, the species appears to exhibit limited competition for resources with native species, as its terrestrial lifestyle and ant-based diet are not shared by sympatric anuran species. Nevertheless, there are a number of ways in which exotic cane toads can exert pressure on native populations, including predation both by and on toads, competition for shelter sites and indirect ecosystem effects. These concerns have been fuelled by largely anecdotal reports of declines in native species immediately following cane toad invasion. Research into the longer-term effects of cane toads on the Australian environment have been equivocal, and suggest little impact from competition for food or nesting/breeding sites. Nevertheless, efforts to control the species to mitigate its ecological effects on native wildlife are a priority in Australian conservation planning and some species of concern, particularly several species of quoll (Dasyurus sp.) have undeniably suffered long-term declines following cane toad invasion, while monitor lizards (Varanus sp.) have consistently suffered from short-term declines immediately following invasion.

 

TAXONOMY

Until 2006, the cane toad was known as Bufo marinus. It was briefly known as Chaunus marinus until this genus, too, was split by taxonomists.

 

REFERENCES

Bufo marinus, Amphibiaweb, University of California
The Cane Toad, CSIRO Entomology 2006
Freeland, W.J. and Kerin, S.H. 1988 Within-habitat relationships between invading B. marinus and Australian species of frog during the tropical dry season. Australian Wildlife Research 15: 293-305

Frost, Darrel R. 2008. Amphibian Species of the World: an Online Reference. Version 5.2 (15 July, 2008). American Museum of Natural History, New York, USA.

Hagman, M. and Shine, R. 2006 Spawning site selection by feral cane toads (Bufo marinus) at an invasion front in tropical Australia. Austral Ecology 31: 551-558
Lever, C. 2001. The cane toad: the history and ecology of a successful colonist. Westbury Academic and Scientific Publishing, Yorkshire, UK
Robinson, M. 1993 A Field Guide to Frogs of Australia, Reed New Holland
Seabrook, W.A. 1993 Habitat use of the cane toad Bufo marinus: implications for assessment of impact and control strategies. PhD thesis, University of Sydney, Australia

Wildlife of Tropical North Queensland, The Queensland Museum 2000

Range            Description            Habitat            Behaviour            Biology            Status            Taxonomy            References

Rhinella marina. Townsville, Queensland, Australia. Note the high ridges above the eyes.