A Guide to the Amphibians
and Reptiles of California

San Nicolas Night Lizard - Xantusia riversiana riversiana

Cope, 1883
Click on a picture for a larger view

Island Night Lizards Range Map
Range in California: Bright Green

Red: San Clemente Night Lizard

observation link

This subspecies of Island Night Lizard is not universally recognized. It occurs exclusively on San Nicolas Island which is currently controlled by the United States Navy and is off limits to the public. I have no pictures of the habitat on the island, but I assume it is similar to the habitat on Santa Barbara Island. The few pictures of the lizards I show below were kindly contributed by a biologist who was there for some biological monitoring with the National Park Service in partnership with the Navy.

San Nicolas Island Wickipedia page.

You can also refer to the very similar subspecies Xantusia riversiana reticulata.

San Nicolas Night Lizard San Nicolas Night Lizard San Nicolas Night Lizard
Adult, San Nicolas Island, Ventura County © Stephanie Root
San Nicolas Night Lizard San Nicolas Night Lizard  
Adult, San Nicolas Island, Ventura County © Stephanie Root Juvenile, San Nicolas Island, Ventura County © Stephanie Root  
2.5 - 4.2 inches long from snout to vent (6.3 - 10.6 cm). (Stebbins 2003)
The largest of the Xantusiids, growing from about 5 - 8 inches long including the tail.

A medium-sized lizard with granular scales, soft skin that appears loose around the neck and shoulders, large plates on the head, lidless eyes with vertical pupils, a gular fold, and a fold of skin low on each side of the body.
Two rows of supraoculars and 16 lengthwise rows of squarish scales at the midbelly.
Color and Pattern
Color and pattern are variable - Brown, olive-brown, grayish, rusty, or yellowish-brown with dark brown or black spots or blotches, sometimes with full or broken light stripes edged with black along the sides of the back.
A reddish brown color is most common and some lizards are uniformly colored above.
(Striped lizards of a different subspecies occur on other islands, and might occur on San Nicolas Island, also.)
The underside is slate bluish, cream or pale yellow. The undersides of the feet are sometimes yellowish.

Life History and Behavior

Once considered nocturnal, but apparently diurnal but sedentary, secretive, and rarely seen.
Spends most of its time under cover, but occasionally seen exposed on the surface in daylight.
The mild climate of San Nicolas Island allows this lizard to remain active throughout the year.
Grows and matures slowly, living to at least 12 years old
Diet and Feeding
Eats small invertebrates including insects, spiders, scorpions, and marine isopods along with plant material (which can make up to one-third of its diet.)
Reproductive potential is low.
Adults do not reach sexual maturity until their 3rd or 4th year and only about half of all females reproduce each year.
Breeds in March and April.
Viviporous, bearing 2-9 live young mostly in September.

Found in almost any island habitat that provides it protection and shade - maritime desert scrub, grassland, chaparral, oak savanna, cactus, dry streambeds, cliffs, rocky beaches, sparsely-vegetated areas.
Takes shelter in cracks in rocks or in the ground, and under surface objects such as rocks, fallen vegetation and beach driftwood.

Geographical Range
Endemic to California.
Found only on San Nicolas Island off the southern California coast.

Notes on Taxonomy
Two subspecies of X. riversiana are still recognized by on the official lists of the SSAR and the CNAH:
X. r. reticulata
X. r. riversiana

"Although not mentioned by Noonan et al. (2013, Mol. Phylogenet. Evol. 69: 109–122), their results support the taxonomic distinction between populations of X. riversiana on San Nicolas Island (X. r. riversiana) and those on San Clemente and Santa Barbara Islands (X. r. reticulata). "
(SSAR Herpetological Circular No. 43, 2017.)

Alternate and Previous Names (Synonyms)

Xantusia riversiana
- Island Night Lizard (Stebbins 1985, 2003)
Klauberina riversiana - Island NIght Lizard (Stebbins 1966)
Xantusia riversiana - Island Night Lizard (Smith 1946, Stebbins 1954)

Conservation Issues  (Conservation Status)
Protected since 1967. Introduced game and livestock and introduced predators such as feral cats and rats have endangered night lizards on the Channel Islands. San Nicolas Island has no more introduced game or livestock, but past overgrazing and its accompanying erosion have removed much of the topsoil.

The U.S. Navy administers San Nicolas Island, and has petitioned to have lizards from the island removed from the Endangered Species List. Reportedly a large number of lizards thrives on the island.

On 4/1/14 the U.S. Fish and Wildlife Service removed Xantusia riversiana, the island night lizard, from the Federal List of Endangered and Threatened Wildlife. More Information
Family Xantusiidae Night Lizards Baird, 1858
Genus Xantusia Night Lizards Baird, 1859 “1858”
Species riversiana Island Night Lizard Cope, 1883

riversiana San Nicolas Night Lizard Cope, 1883
Original Description
Xantusia riversiana - Cope, 1883 - Proc. Acad. Nat. Sci. Philadelphia, Vol. 35, p. 29

from Original Description Citations for the Reptiles and Amphibians of North America © Ellin Beltz

Meaning of the Scientific Name
Xantusia - honors Xantus, John
- honors Rivers, James, J.

from Scientific and Common Names of the Reptiles and Amphibians of North America - Explained © Ellin Beltz

Related or Similar California Lizards
X. henshawi - Granite Night Lizard
X. gracilis - Sandstone Night Lizard
X. vigilis - Yucca Night Lizard
X. sierrae - Sierra Night Lizard
X. r. reticulata - San Clemente Night Lizard

More Information and References
California Department of Fish and Wildlife

US Fish & Wildlife Service

IUCN Red List

Stebbins, Robert C., and McGinnis, Samuel M.  Field Guide to Amphibians and Reptiles of California: Revised Edition (California Natural History Guides) University of California Press, 2012.

Stebbins, Robert C. California Amphibians and Reptiles. The University of California Press, 1972.

Stebbins, Robert C. A Field Guide to Western Reptiles and Amphibians. 3rd Edition. Houghton Mifflin Company, 2003.

Behler, John L., and F. Wayne King. The Audubon Society Field Guide to North American Reptiles and Amphibians. Alfred A. Knopf, 1992.

Powell, Robert., Joseph T. Collins, and Errol D. Hooper Jr. A Key to Amphibians and Reptiles of the Continental United States and Canada. The University Press of Kansas, 1998.

Thelander, C. G., ed. Life on the Edge: A Guide to California's Endangered Natural Resources Volume I: Wildlife. Biosystems Books, Santa Cruz, California. 1994.

Schoenherr, Allan A. Natural History of the Islands of California. The University of California Press. 2003.

Bartlett, R. D. & Patricia P. Bartlett. Guide and Reference to the Turtles and Lizards of Western North America (North of Mexico) and Hawaii. University Press of Florida, 2009.

Jones, Lawrence, Rob Lovich, editors. Lizards of the American Southwest: A Photographic Field Guide. Rio Nuevo Publishers, 2009.

Smith, Hobart M. Handbook of Lizards, Lizards of the United States and of Canada. Cornell University Press, 1946.

Conservation Status

The following status listings are copied from the April 2018 Special Animals List and the 2017 Endangered and Threatened Animals List, both of which are published by the California Department of Fish and Wildlife.

If no status is listed here, the animal is not included on either CDFW list. This most likely indicates that there are no serious conservation concerns for the animal. To find out more about an animal's status, you can go to the NatureServe and IUCN websites to check their rankings.

Check here to see the most current complete lists.

The Special Animals List listing is by full species, it does not recognize this subspecies.

Status Listing
NatureServe Global Ranking G3

Vulnerable—At moderate risk of extinction due to a restricted range, relatively few populations (often 80 or fewer), recent and widespread declines, or other factors.

NatureServe State Ranking S3

Vulnerable in the state due to a restricted range, relatively few populations (often 80 or fewer), recent and widespread declines, or other factors making it vulnerable to extirpation from the state.

U.S. Endangered Species Act (ESA) Delisted
FT - 8/11/77 - Threatened
FPD - 2/4/13 Federally Proposed (Delisting)
Removed from list 4/1/14
California Endangered Species Act (CESA) None
California Department of Fish and Wildlife None
Bureau of Land Management None
USDA Forest Service None
IUCN LC Least Concern


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