Rabb's fringe-limbed treefrog  (Ecnomiohyla rabborum)

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

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). A large frog, it 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. 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’).

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 lives in the forest canopy, and, when threatened, shows a remarkable behaviour, 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. In addition to defending the tree hole, the male’s calls 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 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 species’ habitat 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) (5). However, the species’ situation still remains precarious, with only one female believed to exist in the world (3), and the captive breeding attempts have yet to produce results (1). Field surveys are also continuing in an attempt to locate any remaining wild individuals (1). Sadly, unless captive breeding efforts are successful, the future looks bleak for this remarkable frog.

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

• Zoo Atlanta:
  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.amphibians.org/ASG/Publications_files/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.