Xantusia riversiana


Taxonomy [top]

Kingdom Phylum Class Order Family

Scientific Name: Xantusia riversiana
Species Authority: Cope, 1833
Common Name(s):
English Island Night Lizard
Klauberina riversiana (Cope, 1833)
Taxonomic Notes: This species formerly was placed in the genus Klauberina. Populations on different islands have diverged in coloration, body size, and clutch size, but genetic distances between the island populations are minute compared with those between other species of Xantusia (Bezy et al. 1980).

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2007
Date Assessed: 2007-03-01
Assessor(s): Hammerson, G.A.
Reviewer(s): Cox, N., Chanson, J.S. & Stuart, S.N. (Global Reptile Assessment Coordinating Team)
Listed as Least Concern because, although its extent of occurrence is much less than 5,000 km², it is common and occurs in a habitat that is not under significant threat.
1996 Vulnerable
1994 Rare (Groombridge 1994)
1990 Rare (IUCN 1990)
1988 Rare (IUCN Conservation Monitoring Centre 1988)
1986 Rare (IUCN Conservation Monitoring Centre 1986)

Geographic Range [top]

Range Description: The entire range is on the California Channel Islands in the southwestern United States. The species occurs on San Clemente and Santa Barbara islands (subspecies reticulata) and on San Nicolas Island (subspecies riversiana). It also occurs on a small islet (Sutil Island) 1.3 km offshore from Santa Barbara Island (Bezy et al. 1980). Old records for Santa Catalina Island are erroneous. San Clemente Island, at 145 sq. km, is the largest inhabited island (San Nicolas = 57 sq. km, Santa Barbara = 16 sq. km).
United States (California)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Each island can be regarded as a distinct, single occurrence. Hence there are just a few occurrences or subpopulations. The total adult population size is unknown but greater than 10,000 and perhaps exceeds 100,000. At the time of listing, the population on San Clemente Island was estimated at 800 to 1300 per ha of prime habitat; the San Nicolas Island population was estimated at 14,800; and the Santa Barbara Island population was thought to be 550 to 700 (Matthews and Moseley 1990). However, Fellers and Drost (1991) determined that the total population on Santa Barbara Island was at least 17,600 and concluded that the population is not threatened with extinction as was previously thought. Also Mautz recently found healthy populations on San Clemente Island. USFWS (1990) categorized the status as "stable."
Population Trend: Stable

Habitat and Ecology [top]

Habitat and Ecology: This lizard inhabits grassland, chaparral, oak savanna, clumps of cactus and boxthorn, dry sandy or rocky streambeds, cliffs, and rocky beaches (Stebbins 2003). It occupies areas of thick, low-lying vegetation growing on rocky soil and certain types of rock habitat; dominant plants include patches of prickly pear, matted thickets of boxthorn, and thickets of non-native Australian saltbush (Fellers and Drost 1991, Matthews and Moseley 1990). Individuals are often found under cover of rocks, driftwood, and fallen branches (Stebbins 2003), and they also use burrows.
Systems: Terrestrial

Threats [top]

Major Threat(s): The inhabited islands and their native inhabitants have been negatively affected by habitat alteration and predation resulting from introduction of alien species (e.g., feral cats, goats, pigs, and rabbits). However, according to the Channel Islands Species Recovery Plan of 1984, habitat on the islands "probably has not been altered to the detriment of the [island night] lizards by grazing mammals". Goats and pigs have recently been removed from San Clemente Island. Today, the Island Night Lizard is regarded as not significantly threatened.

Conservation Actions [top]

Conservation Actions: Santa Barbara Island is part of the Channel Islands National Park. The entire island of San Clemente, used for military training, has been designated as Critical Habitat. The species is federally listed as threatened, but delisting may occur in the near future.

Bibliography [top]

Baillie, J. and Groombridge, B. (eds). 1996. 1996 IUCN Red List of Threatened Animals. pp. 378. International Union for Conservation of Nature, Gland, Switzerland and Cambridge, UK.

Bezy, R.L., Gorman, G.C., Adest, G.A. and Kim, Y.J. 1980. Divergence in the island night lizard Xantusia riversiana (Sauria: Xantusiidae). In: D.M. Power (ed.) The California Islands: Proceedings of a Multidisciplinary Symposium, pp. 565-583. Santa Barbara Natural History Museum, Santa Barbara, California.

Fellers, G.M. and Drost, C.A. 1991. Xantusia riversiana. Catalogue of American Amphibians and Reptiles 516: 1-4.

Groombridge, B. (ed.). 1994. 1994 IUCN Red List of Threatened Animals. IUCN, Gland, Switzerland and Cambridge, UK.

IUCN. 1990. IUCN Red List of Threatened Animals. IUCN, Gland, Switzerland and Cambridge, UK.

IUCN. 2007. 2007 IUCN Red List of Threatened Species. Available at: (Accessed: 12th September 2007).

IUCN Conservation Monitoring Centre. 1986. 1986 IUCN Red List of Threatened Animals. IUCN, Gland, Switzerland and Cambridge, UK.

IUCN Conservation Monitoring Centre. 1988. 1988 IUCN Red List of Threatened Animals. IUCN, Gland, Switzerland and Cambridge, UK.

Matthews, J.R. and Moseley, C.J. (eds.). 1990. The Official World Wildlife Fund Guide to Endangered Species of North America. Volume 2. Birds, Reptiles, Amphibians, Fishes, Mussels, Crustaceans, Snails, Insects, and Arachnids. xiii + pp. 561-1180. Beacham Publications, Inc., Washington, D.C.

Stebbins, R.C. 2003. A Field Guide to Western Reptiles and Amphibians. Third Edition. Houghton Mifflin Company, Boston, Massachusetts.

U.S. Fish and Wildlife Service (USFWS). 1990. Endangered and threatened species recovery program: report to Congress. U.S. Fish and Wildlife Service, Washington, D.C.

Citation: Hammerson, G.A. 2007. Xantusia riversiana. The IUCN Red List of Threatened Species. Version 2014.3. <>. Downloaded on 31 March 2015.
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