Rabb's fringe-limbed treefrog (Ecnomiohyla rabborum)

Rabb’s fringe-limbed treefrog (Ecnomiohyla rabborum) was first discovered in 2005, and only described as a new species as recently as 2008 ^{(2) (3)}, but the arrival of a fungal disease in the only known population may since have driven the species to extinction in the wild ^{(3) (4)}. As of early 2012, a single remaining captive individual was believed to be the very last of its kind anywhere in the world ⁽⁵⁾.

A large frog, Rabb’s fringe-limbed treefrog is characterised by substantial webbing on the feet, large discs at the ends of the digits, and scalloped fringes of skin on the outer margins of the forearms and the feet. The head is wider than the body, with a relatively long snout, the top of the head is quite flat, and the eyes are brown. The upper surface of the body is brown, mottled with lighter shades, and the skin is granular in texture. The underside is white with irregular brown spots, while the chin and upper part of the chest are brown ⁽²⁾.

Remarkably, Rabb’s fringe-limbed treefrog has the ability to change the colour of its skin, producing varying amounts of green flecking on the upperparts, flanks and eyelids ⁽²⁾.

Adult male Rabb’s fringe-limbed treefrogs have conspicuous expansions on the upper arm bone (humerus), with black, keratinised spines on the skin covering the projection ⁽²⁾. These structures are likely to be used by the male to grasp the female during mating (‘amplexus’).

Size

Male snout-vent length: 6.2 - 9.7 cm ⁽²⁾

Female snout-vent length: 6.1 - 10 cm ⁽²⁾

Living in the forest canopy, Rabb’s fringe-limbed treefrog shows a remarkable behaviour when threatened, leaping from the treetops and using its outstretched limbs and large, webbed hands and feet to glide through the air ^{(2) (3) (4)}. Individuals have been seen to leap from heights of up to nine metres and land safely on the ground ⁽²⁾. The species is active at night ⁽²⁾, and is likely to feed on a variety of insects, such as crickets and cockroaches ⁽³⁾.

Male Rabb’s fringe-limbed treefrogs appear to be territorial, calling to defend water-filled tree holes in which breeding takes place ^{(2) (3) (4)}. The call consists of a single ‘grrrrrck’, repeated at regular intervals for up to two minutes at a time. Males may call throughout the year, although breeding activity usually peaks between mid-March and May, at the start of the rainy season ⁽²⁾.

In addition to defending the tree hole, the calls of the male Rabb’s fringe-limbed treefrog may serve to attract females to the site, and several females may lay eggs in the hole throughout the year. The eggs are deposited just above the waterline, on exposed bark or wood, with clutch size estimated to range from around 60 to as many as 200 eggs ⁽²⁾.

After laying the eggs, the female Rabb’s fringe-limbed treefrog leaves, but the male remains at the hole and guards the eggs and tadpoles. In an extreme form of parental care, the male may even allow the tadpoles to feed on its skin, which the tadpoles apparently scrape off in small flecks as the male lies half submerged in the water ^{(2) (3) (4)}.

Rabb’s fringe-limbed treefrog is believed to be endemic to the mountains in the immediate vicinity of the town of El Valle de Antón, in the Coclé and Panamá provinces of central Panama. It is so far only known from sites on the Pacific slope of the mountains, but it is possible that it may also be found on the Atlantic slope near Altos de Maria ^{(1) (2) (3) (4)}.

Rabb’s fringe-limbed treefrog inhabits montane cloud forest, at elevations between 900 and 1,150 metres ^{(1) (2) (3) (4)}. Most individuals have been found in primary forest, although some have also been recorded in secondary forest ⁽²⁾.

Rabb’s fringe-limbed treefrog is classified as Critically Endangered on the IUCN Red List ⁽¹⁾.

Rabb’s fringe-limbed treefrog was already uncommon at the time of its discovery, but since the fungal disease chytridiomycosis arrived in the region in 2006, only one individual has been heard calling, in 2007 ^{(1) (2) (3) (4)}. No individuals were detected during field surveys in 2008, and the species may now be extinct in the wild ^{(3) (4)}.

Even if some individuals have survived the disease, the habitat of Rabb’s fringe-limbed treefrog is under threat from forest clearance for the development of luxury holiday homes, and its restriction to a single, small site puts it at particular risk of extinction ⁽¹⁾.

Zoo Atlanta, the Atlanta Botanical Garden and the El Valle Amphibian Conservation Center have been involved in efforts to collect Rabb’s fringe-limbed treefrogs for captive breeding ^{(1) (3) (6)}. Unfortunately, this failed to produce results ⁽¹⁾.

Field surveys are continuing in an attempt to locate any remaining wild individuals of Rabb’s fringe-limbed treefrog ⁽¹⁾. However, in early 2012 one of only two captive individuals died at Zoo Atlanta, meaning that the remaining male at the Atlanta Botanical Garden is likely to be the last Rabb’s fringe-limbed treefrog still in existence anywhere in the world ⁽⁵⁾.

To find out more about Rabb’s fringe-limbed treefrog and its conservation see:

• Zoo Atlanta - Rabb’s fringe-limbed treefrog:
  http://www.zooatlanta.org/home/animals/amphibians/rabbs_fringe_limbed_treefrog
• Amphibia Web:
  http://www.amphibiaweb.org/

For more information on amphibian conservation, including the problems associated with chytridiomycosis, see:

• Gascon, C., Collins, J.P. Moore, R.D., Church, D.R., McKay, J.E. and Mendelson III, J.R. (2007) Amphibian Conservation Action Plan. IUCN/SSC Amphibian Specialist Group, Gland, Switzerland and Cambridge, UK. Available at:
  http://www.amphibianark.org/pdf/ACAP.pdf
• Amphibian Ark:
  http://www.amphibianark.org/
• IUCN / SSC Amphibian Specialist Group:
  http://www.amphibians.org/
• Collins, J.P and Crump, M.L. (2009) Extinction in Our Times: Global Amphibian Decline. Oxford University Press, Oxford.

Authenticated (03/07/10) by Dr Joseph R. Mendelson III, Curator of Herpetology, Zoo Atlanta.
http://www.zooatlanta.org/

Cloud forest

A tropical mountain forest, with a high incidence of cloud cover throughout the year.

Endemic

A species or taxonomic group that is only found in one particular country or geographic area.

Keratin

A group of fibrous proteins that form the basis of hair, nails, wool etc in animals.

Primary forest

Forest that has remained undisturbed for a long time and has reached a mature condition.

Secondary forest

Forest that has re-grown after a major disturbance, such as fire or timber harvest, but has not yet reached the mature state of primary forest.

Territorial

Describes an animal, a pair of animals or a colony that occupies and defends an area.

1. IUCN Red List (May, 2010)
   http://www.iucnredlist.org/
2. Mendelson III, J.R., Savage, J.M., Griffith, E., Ross, H., Kubicki, B. and Gagliardo, R. (2008) Spectacular new gliding species of Ecnomiohyla (Anura: Hylidae) from Central Panama. Journal of Herpetology, 42(4): 750-759.
3. Zoo Atlanta - Rabb’s fringe-limbed treefrog (May, 2010)
   http://www.zooatlanta.org/home/animals/amphibians/rabbs_fringe_limbed_treefrog
4. Amphibia Web (May, 2010)
   http://www.amphibiaweb.org/
5. Zoo Atlanta: Press release - Zoo Atlanta frog was one of only two of his kind left on Earth (February, 2012)
   http://www.zooatlanta.org/media/file/021712_ZooAtl_rabbs_euthanized.pdf
6. Mendelson III, J.R. (July, 2010) Pers. comm.