Holdridge's Toad

The adult male is between 32 and 46 mm snout vent length (SVL). The adult female is slightly larger, measuring between 38 and 53 mm SVL. Both the male and female have similar dorsum coloration ranging from black to light brown with a lighter colored venter. The limbs, as well as the dorsal and lateral surfaces are spotted with reddish warts of varying sizes. The head is broad with low crests, excluding the thicker supratympanic crest. The reddish colored parotoid gland is smooth and globular. Limbs are shortened and feature fleshy hands and feet that are moderately webbed and lack tubercles. Both males and females of the species lack structures of the ear, causing deafness. Males lack vocal slits and sac, and have unusually hypertrophied testes. Incilius holdridgei tadpoles are small in size with ovoid-shaped bodies that are dark brown in color and feature a lighter venter surface. The tail and caudal fins are rounded. The mouth is directed ventrally and the oral disc has beaks and 2 to 3 rows of denticles which are bordered by a row of large papillae.

Originally found on Barva Volcano in Cordillera Central, Costa Rica, the Holdridge's toad is still endemic to that small area of Costa Rica's montane rainforests. They occur in an elevation range of 1,900 to 2,200 m (6,200 to 7,200 ft). Holdridge's toads have been mainly observed in the rainforests of the Central Mountain Range of Costa Rica. The species has recently been found living in open grassy areas. This class of toads settles below the leaf litter inside the forest during the duration of excessive rainfall. They are classified as a fossorial species due to the act of digging or burrowing themselves. They favor mossy stream banks.

Incilius holdridgei are fossorial, and remain relatively inactive while burrowed underground. During seasons of heavy rain, they can be found underneath layers of forest floor debris. During dryer periods, they can be found near stream banks. Members of the species become more active during the daytime when they are above ground or crepuscular time. Due to their morphology, Incilius holdridgei are deaf and mute; they apparently do not communicate through sound or have mating calls- a rarity among frogs and toads. Before 1986, the species had been relatively easy to spot during its two-month mating season from April to May when males and females became more active and gathered in the hundreds. However, outside of the mating season, the toads were very difficult to locate.

Diet. The Holdridge's toads' diet includes a broad range of arthropod invertebrates, among them spiders, larval stages of moths and butterflies (lepidopterans), flies, beetles, earwigs (dermoptera), ants, and mites.

Reproduction. The average age for sexual maturity of Incilius holdridgei is about three years. Due to the lack of development of vocal slits and tympana Incilius holdridgei do not have a breeding call. This species is an explosive breeder that lays clutches of large eggs in pools of water on the forest floor, they are also known to lay eggs in man-made drainage ditches. …

Holdridge's toad was declared extinct in 2008 because it had not been observed since 1986. Between 1968 and 2009 there were no sightings of Holdridge's toad in their natural environment. Extensive searches were led to determine if the species was extinct. The searches lasted for seven years before the toad was declared extinct. From 2008 to 2010, there was extensive searching efforts for the species. In 2009, tadpole and adult toads were discovered in two separate ponds that reclassified the species as critically endangered. The search suggested that the adult population is less than 50 mature individuals, leading to its listing as Critically Endangered. Juveniles were found, indicating relatively recent reproductive activity, but no large aggregations were seen; this species is considered Critically Endangered. Multiple causes are believed to have led to the toad's presumed extinction, including chytridiomycosis, climate change, and deforestation. The main threat to Holdridge's toad is thought to be chytridiomycosis, a fungal pathogen, Batrachochytrium dendrobatidis, that causes an infections disease in amphibians. The fungus keratinizes any keratin-containing skin layers in both the tadpoles and adult frogs. High levels of this fungus were detected in the breeding grounds of Holdridge's toad before and after the species was presumed extinct. Another proposed threat to I. …