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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.
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| Adult, San Nicolas Island, Ventura County © Stephanie Root |
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| Adult, San Nicolas Island, Ventura County © Stephanie Root |
Adult, San Nicolas Island, Ventura County © Stephanie Root |
Juvenile, San Nicolas Island, Ventura County © Stephanie Root |
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| Description |
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| Size |
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.
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| Appearance |
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.
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| Life History and Behavior |
Activity |
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.
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| Defense |
The tail can break off easily, but it will grow back.
The detached tail wriggles on the ground which can distract a predator from the body of the lizard allowing it time to escape.
More information about tail loss and regeneration. |
| Longevity |
| 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.) |
| Reproduction |
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.
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| Habitat |
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.
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| Geographical Range |
Endemic to California.
Found only on San Nicolas Island off the southern California coast.
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| 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)
Xantusia riversiana - Island Night Lizard (Rivers's Lizard) (Grinnell and Camp 1917)
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| 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 |
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Taxonomy |
| Family |
Xantusiidae |
Night Lizards |
Baird, 1858 |
| Genus |
Xantusia |
Night Lizards |
Baird, 1859 “1858” |
| Species |
riversiana |
Island Night Lizard |
Cope, 1883 |
Subspecies
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riversiana |
San Nicolas Night Lizard |
Cope, 1883 |
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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
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Meaning of the Scientific Name |
Xantusia - honors Xantus, John
riversiana - honors Rivers, James, J.
from Scientific and Common Names of the Reptiles and Amphibians of North America - Explained © Ellin Beltz
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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
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More Information and References |
California Department of Fish and Wildlife
US Fish & Wildlife Service
IUCN Red List
Robert L. Bezy. Night Lizards: Field Memoirs and a Summary of the Xantusiidae. ECO Herpetological Publishing & Distribution. 2019.
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.
Flaxington, William C. Amphibians and Reptiles of California: Field Observations, Distribution, and Natural History. Fieldnotes Press, Anaheim, California, 2021.
Samuel M. McGinnis and Robert C. Stebbins. Peterson Field Guide to Western Reptiles & Amphibians. 4th Edition. Houghton Mifflin Harcourt Publishing Company, 2018.
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.
Joseph Grinnell and Charles Lewis Camp. A Distributional List of the Amphibians and Reptiles of California. University of California Publications in Zoology Vol. 17, No. 10, pp. 127-208. July 11, 1917.
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The following conservation status listings for this animal are taken from the January 2024 State of California Special Animals List and the January 2024 Federally Listed Endangered and Threatened Animals of California list (unless indicated otherwise below.) Both lists are produced by multiple agencies every year, and sometimes more than once per year, so the conservation status listing information found below might not be from the most recent lists. To make sure you are seeing the most recent listings, go to this California Department of Fish and Wildlife web page where you can search for and download both lists:
https://www.wildlife.ca.gov/Data/CNDDB/Plants-and-Animals.
A detailed explanation of the meaning of the status listing symbols can be found at the beginning of the two lists. For quick reference, I have included them on my Special Status Information page.
If no status is listed here, the animal is not included on either 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 also go to the NatureServe and IUCN websites to check their rankings.
The July 2023 Special Animals List and Federally Listed Endangered and Threatened Animals of California list desinations apply to the full species, Xantusia riversiana - Island Night Lizard.
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| Organization |
Status Listing |
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| NatureServe Global Ranking |
G3 |
Vulnerable
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| NatureServe State Ranking |
S3 |
Vulnerable
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| U.S. Endangered Species Act (ESA) |
Recovered & Delisted |
FT - Listed as Threatened 9/12/1977
FPD - Federally Proposed (Delisting) 2/4/2013
Recovered - Removed from ESA list 5/1/2014
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| California Endangered Species Act (CESA) |
None |
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| California Department of Fish and Wildlife |
None |
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| Bureau of Land Management |
None |
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| USDA Forest Service |
None |
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| IUCN |
LC |
Least Concern |
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