Darwin’s frog (Rhinoderma darwinii)

Also known as: Darwin’s toad
  
Spanish: Rana Narigona, Ranita De Darwin, Sapito Partero, Sapito Vaquero
KingdomAnimalia
PhylumChordata
ClassAmphibia
OrderAnura
FamilyCycloramphidae
GenusRhinoderma (1)
SizeMale length: 2.2 – 2.8 cm (2)
Female length: 2.5 – 3.1 cm (2)

The Darwin’s frog is classified as Vulnerable (VU) on the IUCN Red List (1).

Discovered by Charles Darwin in the thick, gloomy forests of southern-central Chile, Darwin’s frog (Rhinoderma darwinii) possesses a distinctive appearance and an unusual biology (2) (3). The head of this species has a triangular appearance due to the presence of a pronounced, fleshy proboscis that projects from the tip of the snout. The colouration of the warty upperparts is variable, with individuals exhibiting various shades of brown, green or a mixture of the two. By contrast the underparts are invariably black and white with large blotches (2). The male Darwin’s frog possesses a large vocal sac, extending from beneath the throat, over the belly, to the groin. Rather than enabling the male to produce a booming call, this sac has an unusual role in brooding offspring, and the call is, in fact, small and bell-like (4).

Darwin’s frog occupies the austral forest of southern-central Chile and Argentina. This species is most abundant on the Chiloé Archipelago, Chile, and scarce within Argentina, where it is only known from the province of Neuquen and Río Negro. It can be found between altitudes of 50 to 1,500 metres above sea-level (1) (2).

Generally found on land (4), Darwin’s frog inhabits moist leaf-litter, often along the banks of slow moving streams and within boggy areas, in cool, temperate forests (2).

Mainly active during the day, Darwin’s frog frequently basks in sunlight, while camouflaged amongst the leaf litter. This species mainly feeds upon insects and other small invertebrates, which it catches by remaining motionless and waiting for the unsuspecting animal to come near, before lunging forwards and devouring its prey. When threatened Darwin’s frog will play dead, rolling onto its back and lying motionless, or, more dramatically, it will leap into a stream, and float in the water on its back, again feigning death (2).

The male Darwin’s frog produces vocalisations throughout the year, but mainly during the breeding season, which occurs from November to March. After encountering a prospective mate, the male leads the female to a sheltered site where courtship and egg-laying take place. The female deposits a clutch of around 40 eggs, each four millimetres wide, in the leaf litter, which are fertilised by the male. The female then departs, but the male remains with the eggs, guarding them while they develop (2). After around 20 days, when the tadpoles begin to wriggle within the eggs, the male uses its tongue to pick up the eggs, and manoeuvres them through the slits in its mouth into the vocal sac (2) (4). Here, the tadpoles hatch from the eggs and remain while metamorphosis takes place. While in the sac, the tadpoles are sustained by the remainders of the yolk from the egg, as well as nutrient-rich secretions produced by the adult (2). Once development has progressed to the point where the young are around 1 cm long and the tail has become reduced to a small stump, they move out of the vocal sac and are released by the male out of the mouth (4). As many as 19 tadpoles may be brooded by a single male, causing the internal organ’s to distort to accommodate the mass of offspring, but returning to normal after the froglets are released (2) (4).

In recent years, Darwin’s frog has undergone a worrying decline throughout its range, with some populations in Chile disappearing entirely (1). While in some areas, particularly in the northern part of this species’ range, the decline can be attributed to deforestation and replacement of native trees with exotic pine or eucalyptus species, in other regions, which are more remote or protected, the cause is unknown (2). It may, however, be linked to global changes in climate and increased ultraviolet radiation, which are believed to be contributing to the ongoing worldwide decline in amphibians (2) (5).

Darwin’s frog is located in several protected areas throughout its range, which are helping to preserve its dwindling habitat. Nevertheless, there is a need for improved maintenance of existing sites, as well as expansion of the protected area network, especially in the more heavily exploited northern parts of this species’ range. In order to understand the causes of the unexplained decline of Darwin’s frog in apparently suitable areas of habitat, the population must be closely monitored. This should then inform the development of a conservation strategy for this imperilled species (1).

For further information on Darwin's frog see:

To learn more about the worldwide decline of amphibians and what can be done to stop it, visit:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
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  1. IUCN Red List (April, 2009)
    http://www.redlist.org/
  2. AmphibiaWeb – Darwin’s frog (April, 2009)
    http://amphibiaweb.org/cgi/amphib_query?query_src=aw_lists_genera_&where-genus=Rhinoderma&where-species=darwinii
  3. Bell, T. and Darwin, C.R. (1843) Reptiles Part 5 No. 2 of The Zoology of the Voyage of H.M.S. Beagle. Smith Elder and Co, London. Available at:
    http://darwin-online.org.uk/
  4. Burton, M. and Burton, R. (2002) International Wildlife Encyclopedia. Marshall Cavendish, New York.
  5. AmphibiaWeb (April, 2009)
    http://www.amphibiaweb.org/declines