Scinax alcatraz
Alcatraz snouted treefrog
family: Hylidae
subfamily: Hylinae
Conservation Status (definitions)
IUCN (Red List) Status Critically Endangered (CR)
Other International Status None
National Status None
Regional Status None


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Scinax alcatraz is a large-sized member of the S. perpusillus group (males: 19.7–24.4 mm SVL; females 27.0–29.8 mm SVL). Like all members of the S. perpusillus group, S. alcatraz has extremely reduced webbing between toes II and III (Peixoto 1987). The dorsal skin texture is smooth or has some scattered pustules (Faivovich et al. 2010). Hidden surfaces of limbs have yellow coloration (Leão 1950). Most Scinax alcatraz have dorsal markings but some individuals do not (Faivovich et al. 2010). Inguinal glands are visible (and present in both males and females), a character shared with S. perpusillus group members S. belloni and S. littoreus (Faivovich et al. 2010). Males have glandular nuptial pads (Faivovich et al. 2010).

It is an island endemic and there are no other congeners present on Ilha dos Alcatrazes. S. alcatraz can be distinguished from S. peixotoi, which occurs on a different Brazilian island (Ilha de Queimada Grande), by its larger size (S. peixotoi males 18.8–20.7 mm SVL, females 22.4–25.1 mm SVL), narrower head, a loreal region that is not concave, less distinct canthus rostralis, less prominent eyes, shorter internarial distance, less rugose dorsal skin, and a less ornamented dorsum (Brasileiro et al. 2007a). S. alcatraz can be distinguished from S. faivovichi, which occurs on a third Brazilian island (Ilha de Porcos Pequena), by its larger size, less protruding snout, less triangular head, less prominent eyes, less distinct canthus rostralis, a loreal region that is not concave, lack of dark stripes on the arms, and less patterned dorsum (Brasileiro et al. 2007c).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Brazil


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It only occurs on Ilha dos Alcatrazes, a 149 ha island about 35 km off the northern coast of the State of Sao Paulo, southeastern Brazil. The maximum elevation is about 100 m asl. This species is found in both primary and secondary forest, and has also been recorded from degraded forest (Stuart et al. 2008).

Life History, Abundance, Activity, and Special Behaviors
Members of the S. perpusillus group are bromeliad-breeders (Peixoto 1987). This species spends its entire life cycle (eggs, tadpoles, adults) in bromeliads (Brasileiro, pers. obs. cited in Brasileiro et al. 2007b).

Trends and Threats
Listed as Critically Endangered because all individuals are in a single location on the Ilha de Alcatrazes, and there is continuing decline in the extent and quality of its habitat on the Ilha de Alcatrazes, southern Brazil. Ilha de Alcatrazes was used as a military base in the past, but this is no longer the case. Although there currently is no human settlement on the island, direct disturbance of the species, and degradation of its habitat from touristic activities and fire are ongoing threats. There are no protected areas established on the island. Further survey work is required to determine the biology and population status of this species (Stuart et al. 2008).

Possible reasons for amphibian decline

General habitat alteration and loss
Loss of genetic diversity from small population phenomena

This species was described by Lutz (1973) and was subsequently thought to be a subspecies of Scinax catherinae. Scinax alcatraz was removed from synonymy with Scinax catharinae by Peixoto (1988).

Scinax alcatraz is one of a number of species currently recognized in the S. perpusillus group (including S. alcatraz, S. arduous, S. atratus, S. belloni, S. faivovichi, S. littoreus, S. melloi, Scinax peixotoi, S. perpusillus, Scinax tupinamba and S. v-signatus). The S. perpusillus group was first proposed by Peixoto (1987) and includes small species that reproduce exclusively in bromeliads and are distributed in Atlantic tropical coastal forest, ranging from Espirito Santo to Santa Catarina, Brazil. Frogs in this group have extreme reduction in webbing between toes II and III (Peixoto 1987; Faivovich 2002).

Other frog species present on the Ilha dos Alcatrazes include Leptodactylus marmoratus and the insular species Cycloramphus faustoi (Brasileiro et al. 2007b). L. marmoratus is a leaf-litter dweller, while C. faustoi is found in rock crevices.


Brasileiro, C. A., Haddad, C. F. B., Sawaya, R. J., and Martins, M. (2007). ''A new and threatened species of Scinax (Anura: Hylidae) from Queimada Grande Island, southeastern Brazil.'' Zootaxa, 1391, 47-55.

Brasileiro, C. A., Haddad, C. F. B., Sawaya, R. J., and Sazima, I. (2007). ''A new and threatened island-dwelling species of Cycloramphus (Anura: Cycloramphidae) from southeastern Brazil.'' Herpetologica, 63, 501-510.

Brasileiro, C. A., Oyamaguchi, H. M., and Haddad, C. F. B. (2007). ''A new island species of Scinax (Anura: Hylidae) from southeastern Brazil.'' Journal of Herpetology, 41, 271-275.

Brasileiro, C.A., and Oyamaguchi, H.M. (2006). ''Scinax alcatraz (Alcatraz snouted treefrog). Predation.'' Herpetological Review, 37, 451.

Faivovich, J. (2002). ''A cladistic analysis of Scinax (Anura, Hylidae).'' Cladistics, 18, 367-393.

Faivovich, J., Gasparini, J. L., and Haddad, C. F. B. (2010). ''A new species of the Scinax perpusillus group (Anura: Hylidae) from Espírito Santo, Brazil.'' Copeia, 2010, 97-102.

Leão, A. T. (1950). ''Sobre dos batráquios da ilha dos Alcatrazes.'' Memórias do Instituto Butantan, 22, 63-70.

Lutz, B. (1973). ''New Brazilian forms of Hyla .'' Boletim Museu Nacional Rio de Janeiro Zoologia, 288, 1-7.

Peixoto, O. L. (1987). ''Caracterizacao do grupo ‘‘perpusillus’’ e revalidacao da posicao taxonomica de Ololygon perpusilla perpusilla e Ololygon perpusilla vsignata (Amphibia, Anura, Hylidae).'' Arquivos da Universidade Federal Rural do Rio de Janeiro, 10, 37-49.

Peixoto, O. L. (1988). ''Sobre o ''status'' taxonômico de Hyla catharinae alcatraz B. Lutz 1973, com a descrição de uma nova espécie para o grupo perpusilla (Amphibia, Anura, Hylidae).'' Acta Biological Leopoldensia, 10, 253-267.

Stuart, S., Hoffmann, M., Chanson, J., Cox, N., Berridge, R., Ramani, P., and Young, B. (eds) (2008). Threatened Amphibians of the World. Lynx Edicions, IUCN, and Conservation International, Barcelona, Spain; Gland, Switzerland; and Arlington, Virginia, USA.

Written by Meghan Bishop (Meghanrbishop AT, San Francisco State University
First submitted 2010-06-24
Edited by Kellie Whittaker (2011-03-10)

Species Account Citation: AmphibiaWeb 2011 Scinax alcatraz: Alcatraz snouted treefrog <> University of California, Berkeley, CA, USA. Accessed Oct 22, 2017.

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Citation: AmphibiaWeb. 2017. <> University of California, Berkeley, CA, USA. Accessed 22 Oct 2017.

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