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Eleutherodactylus cooki

ListedJune 11, 1997
DescriptionLarge solid brown frog, approximately 3.3 in (8.4 cm) long.
HabitatCrevices and grottoes in and among boulders.
ReproductionEggs laid on humid faces of boulders.
ThreatsHabitat degradation and loss due to land conversion to agriculture, deforestation and earth movement for rural development, road construction, and dam construction for the formation of a reservoir.
RangePuerto Rico


Eleutherodactylus, the largest vertebrate genus with more than 400 described species, has northwestern South America and the West Indies as its two centers of species diversity. Almost all species share two characteristics: T-shaped terminal phalangesprobably an adaptation for climbingand direct development, allowing for reproduction away from water. In the West Indies, Eleutherodactylus species are a dominant amphibian group. No single species is naturally found on more than one of the four Greater Antilles, and most are restricted to small areas within an island. Seventeen species of this genus are known from Puerto Rico, and collectively they are commonly known as coquis.

The guajón, Eleutherodactylus cooki, known commonly as demonio de Puerto Rico (demon of Puerto Rico) is a relatively large frog, approximately 3.3 in (8.4 cm) in length. It is solid brown in color, although attending and calling males may have a yellow throat. The guajón may be the only species of Eleutherodactylus in Puerto Rico that exhibits sexual dimorphism in color. Both sexes of these frogs have large white-rimmed eyes, giving the species a specter or phantomlike appearance. The species is characterized by having large truncate discs and a peculiar, low, and melodious voice which is completely different from any other species of Eleutherodactylus in Puerto Rico.


The number of egg clutches and juveniles was observed to be greatest during the months of October and September. Eggs are laid on the humid faces of boulders in protected microhabitats within the grottoes and up to 59 eggs, which may actually be multiple clutches, are apparently guarded by the males. Diurnal activity of the guajón occurs only inside the caves. Many guajóns, however, have been observed leaving the caves at dusk, presumably to forage and rehydrate, and returning before dawn.


The guajón lives in crevices and grottoes in and among boulders. Such grottoes are commonly referred to as guajónales. This species derives its name from the grottoes or guajónales where the frogs live. The species is apparently limited in distribution by where this rock formation occurs.


The guajón, first collected by Chapman Grant in 1932, is a habitat specialist now only known from the municipalities of Yabucoa, San Lorenzo, Humacao, and Las Piedras in the Pandura range in the extreme southeastern corner of Puerto Rico. During surveys conducted in 1986, 1992, and 1996, the guajón was found at its historical localities, all of which occur within the municipalities of Yabucoa and San Lorenzo. Dr. Fernando Bird also reports the species from the municipalities of Las Piedras and Humacao. Little historical data is available on abundance; therefore, reductions in populations are difficult to document. The guajón is extremely restricted in geographical distribution and occurs only on privately owned lands. Scientists have documented population fluctuations, apparently related to precipitation and temperature. Numbers are lowest during the winter months, during the period of least rainfall and lowest temperatures.


The major threat to the species is habitat degradation and loss, most of which has been caused by land conversion to agriculture, deforestation and earth movement for rural development, road construction, and dam construction for the formation of a reservoir. Deforestation often leads to more frequent flash floods, resulting in the drowning of adult guajóns and the destruction of nests. The practice of planting crops right up to the entrance of the caves may eliminate nocturnal habitat of the species and increase the pesticide and fertilizer runoff into the water flowing under the caves. Caves are also often used as garbage dumps. The heavy cut and fill associated with road construction has eliminated habitat; a major four-line highway is currently proposed through the area, as is the construction of a major reservoir.

Disease has not been documented as a factor in the decline of this species. However, examination of both preserved and live specimens of the guajón have revealed that the species is parasitized by the tick Ornithodoros talaje. Nevertheless, the effect of this parasite on the guajón has yet to be studied. Nocturnally active introduced species such as cats, rats, and mongoose may adversely affect densities of this species by feeding on the frogs and their eggs. There is also the possibility that guajón individuals have been killed out of fear by local people; at least one scientist has noted that many people seem to be afraid of the appearance of these frogs. The peculiar calling and phantomlike appearance of this frog made many local people fearful of the species, believing that the mere sight of one would be fatal.

Other threats are more generalized in nature, though none the less threatening for that. In recent years there has been a pronounced decline in global populations of amphibians. Factors that may be responsible for this worldwide decline of amphibians include habitat destruction and modification, acid rain, pesticide contamination, introduction of non-native predators and competitors, agriculture, mining and logging, increased levels of ultraviolet radiation, collection, and global climatic change.

Flash floods, droughts, and catastrophic stormssuch as Hurricane Hugo in 1989may have caused localized extirpations of other species of Eleutherodactylus in specific areas in Puerto Rico. Hurricane Hugo decreased the numbers of E. portoricensis, a species restricted in distribution which is not abundant.

Conservation and Recovery

Although not previously identified as a determinant factor in the decline of the guajón specifically, scientific collecting of related species of coqui in Puerto Rico may well have contributed to declines. In a survey of only seven museums in both Puerto Rico and the United States, numerous specimens of the web-footed coqui (E. karlschmidti ) and the mottled coqui (E. eneidae ) were located. The specimens totaled 473 preserved individuals of the former and 325 of the latter species. The status of both these related species are now being evaluated by the U.S. Fish and Wildlife Service because of their extreme rarity. Collection of other Eleutherodactylus species for use in local art has also been documented, and this activity is currently being evaluated by the Commonwealth government for possible regulation.


U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345

Caribbean Field Office
U.S. Fish and Wildlife Service
P.O. Box 491
Boquerón, Puerto Rico 00622
Telephone: (809) 851-7297


Drewry, G. E. 1986. "Golden Coqui Recovery Survey and Brief Status Evaluation of Five Other Puerto Rican Eleutherodactylus Species." Caribbean Field Office: U.S. Fish and Wildlife Service.

Joglar, R. L. 1992. "Status Survey of Four Species ofEleutherodactylus : Final Report." Caribbean Field Office: U.S. Fish and Wildlife Service.

Powell, R., and R. W. Henderson, eds. 1996. "Biology of the Puerto Rican Cave-dwelling Frog, Eleutherodactylus cooki. " Contributions to West Indian Herpetology 12: 251-258.

Powell, R., and R. W. Henderson, eds. 1996. "Declining Amphibian Populations in Puerto Rico." Contributions to West Indian Herpetology 12: 371-380.

U. S. Fish and Wildlife Service. 11 June 1997. "Threatened Status for the Guajón." Federal Register 62 (112): 31757-31762.

Wake, D. B., and H. J. Morowitz. 1991. "Declining Amphibian Populationsa Global Phenomenon Findings and Recommendations." Alytes 9 (2): 33-42.