Xantusia riversiana - Cope, 1883
Island Night Lizard
Synonym(s): Klauberina riversiana
Taxonomic Status: Accepted
Related ITIS Name(s): Xantusia riversiana Cope, 1883 (TSN 174091)
Unique Identifier: ELEMENT_GLOBAL.2.106467
Element Code: ARACK01020
Informal Taxonomy: Animals, Vertebrates - Reptiles - Lizards
 
Kingdom Phylum Class Order Family Genus
Animalia Craniata Reptilia Squamata Xantusiidae Xantusia
Genus Size: B - Very small genus (2-5 species)
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Concept Reference
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Concept Reference: Collins, J. T. 1990. Standard common and current scientific names for North American amphibians and reptiles. 3rd ed. Society for the Study of Amphibians and Reptiles. Herpetological Circular No. 19. 41 pp.
Concept Reference Code: B90COL01NAUS
Name Used in Concept Reference: Xantusia riversiana
Taxonomic Comments: 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).

This species could have occurred on San Clemente Island as early as the Miocene or Pliocene; its disappearance from the mainland may date from pre-Nebraskan time (Bezy et al. 1980).
Conservation Status
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NatureServe Status

Global Status: G3
Global Status Last Reviewed: 02Sep2014
Global Status Last Changed: 02Sep2014
Rounded Global Status: G3 - Vulnerable
Reasons: Range includes only a few islands off the coast of southern California; recent surveys indicate the presence of substantial populations; threats on the islands have been reduced.
Nation: United States
National Status: N1 (05Oct1996)

U.S. & Canada State/Province Status
United States California (S3)

Other Statuses

IUCN Red List Category: LC - Least concern

NatureServe Global Conservation Status Factors

Range Extent: 100-250 square km (about 40-100 square miles)
Range Extent Comments: The entire range is on the California Channel Islands. 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 square kilometers, is the largest inhabited island (San Nicolas = 57 sq km, Santa Barbara = 16 sq km).

Area of Occupancy: 26-2,500 4-km2 grid cells
Area of Occupancy Comments:  

Number of Occurrences: 1 - 5
Number of Occurrences Comments: Each island can be regarded as a distinct, single occurrence. Hence there are just a few occurrences or subpopulations.

Population Size: 10,000 - 1,000,000 individuals
Population Size Comments: 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 800-1300 per hectare of prime habitat; the San Nicolas Island population was estimated at 14,800; and the Santa Barbara Island population was thought to be 550-700 (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.

Overall Threat Impact: Low
Overall Threat Impact Comments: The inhabited islands and their native inhabitants have been negatively affected by habitat alteration and predation resulting from introduction of exotic 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.

Short-term Trend: Relatively Stable (<=10% change)
Short-term Trend Comments: USFWS (1990) categorized the status as "stable."

Long-term Trend: Decline of <30% to increase of 25%

Intrinsic Vulnerability: Moderately vulnerable
Intrinsic Vulnerability Comments: Low reproductive potential.

Other NatureServe Conservation Status Information

Inventory Needs: Census periodically to determine population numbers, fluctuations, and rates of reproduction.

Protection Needs: The following protection/management needs have been idientified: remove feral cats and other feral animals such as goats and pigs from habitat; encourage a continued trend toward recovery of native plant communities (Fellers and Drost 1991). See "Recovery plan for the endangered and threatened species of the California Channel Islands" (1984).

Distribution
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Global Range: (100-250 square km (about 40-100 square miles)) The entire range is on the California Channel Islands. 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 square kilometers, is the largest inhabited island (San Nicolas = 57 sq km, Santa Barbara = 16 sq km).

U.S. States and Canadian Provinces
Color legend for Distribution Map
Endemism: endemic to a single state or province

U.S. & Canada State/Province Distribution
United States CA

Range Map
Note: Range depicted for New World only. The scale of the maps may cause narrow coastal ranges or ranges on small islands not to appear. Not all vagrant or small disjunct occurrences are depicted. For migratory birds, some individuals occur outside of the passage migrant range depicted.

Range Map Compilers: NatureServe, 2005


U.S. Distribution by County Help
State County Name (FIPS Code)
CA Los Angeles (06037), Santa Barbara (06083), Ventura (06111)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
18 San Pedro Channel Islands (18070107)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A lizard with an adult snout-vent length of 6.2-9.4 cm.
General Description: A lizard with lidless eyes, vertical pupils, soft pliable skin, granular dorsal scales, large squarish ventral scales, a gular fold, and a fold of skin low on each side of the body; back is mottled with pale ash gray or beige and yellowish brown, darkened with varying amounts of black; some may be uniformly colored above (San Nicolas Island) and some have a pale gray stripe on each side of upper body, edged with brown and black; a brown middorsal stripe may be present (Stebbins 1985).
Diagnostic Characteristics: Differs from other night lizards in having (1) 16 instead of 14 or 12 lengthwise rows of squarish scales at midbelly and (2) two rows of supraoculars (Stebbins 1985).
Reproduction Comments: Viviparous. Breeds in April (begins in March according to Matthews and Moseley 1990). Gestation lasts 14 weeks (Fish and Wildlife Service 1980). Female gives birth to 2-9 young mostly in September (Stebbins 1985, Fellers and Drost 1991). Estimated to reach sexual maturity in 3rd or 4th year. Reproductive potential is low. Only about half of the female population is estimated to be reproductively active in a given year. Slow growing, some living to at least 12 years old (Fellers and Drost 1991).
Ecology Comments: Sedentary; on Santa Barbara Island, home range averaged 17 sq m and population density exceeded 3200/ha in boxthorn habitat (Fellers and Drost 1991). Exceedingly secretive. Apparently incurs heavy predation by introduced and native birds and mammals.
Non-Migrant: Y
Locally Migrant: N
Long Distance Migrant: N
Terrestrial Habitat(s): Bare rock/talus/scree, Cliff, Grassland/herbaceous, Shrubland/chaparral, Woodland - Hardwood
Special Habitat Factors: Burrowing in or using soil, Fallen log/debris
Habitat Comments: This lizard inhabits grassland, chaparral, oak savannah, 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.
Adult Food Habits: Invertivore
Immature Food Habits: Invertivore
Food Comments: Preys on various terrestrial insects and spiders; also centipedes, scorpions, and marine isopods, as well as stems, leaves, flowers, and seeds (Stebbins 1985, Fellers and Drost 1991). May also consume small lizards.
Adult Phenology: Diurnal
Immature Phenology: Diurnal
Phenology Comments: Exclusively diurnal; inactive in cold temperatures and extreme heat.
Length: 21 centimeters
Economic Attributes Not yet assessed
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Management Summary
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Biological Research Needs: Research needed on reproductive biology and ecology of this species.
Population/Occurrence Delineation
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Group Name: Night Lizards (Xantusiids)

Use Class: Not applicable
Minimum Criteria for an Occurrence: Occurrences are based on evidence of historical presence, or current and likely recurring presence, at a given location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals (including eggs) in or near appropriate habitat where the species is presumed to be established and breeding.
Separation Barriers: Busy highway or highway with obstructions such that lizards rarely if ever cross successfully; major river, lake, pond, or deep marsh; densely urbanized area dominated by buildings and pavement.
Separation Distance for Unsuitable Habitat: 1 km
Separation Distance for Suitable Habitat: 3 km
Separation Justification: Xantusiids appear to be exceptionally sedentary. On Santa Barbara Island, home range of Xantusia riversiana, the largest species in the United States, averaged only 17 sq m (Fellers and Drost 1991). However, nothing is known about dispersal distances. Despite sedentary habits, it seems unlikely that location separated by less than a few kilometers of suitable habitat would represent independent occurrences over the long term.
Inferred Minimum Extent of Habitat Use (when actual extent is unknown): .1 km
Date: 10Sep2004
Author: Hammerson, G.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 07Apr2011
NatureServe Conservation Status Factors Author: Jefferson, J., & G. Hammerson
Element Ecology & Life History Edition Date: 31Aug2005
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
Help
  • Behler, J. L., and F. W. King. 1979. The Audubon Society field guide to North American reptiles and amphibians. Alfred A. Knopf, New York. 719 pp.

  • Bezy, R. L., et al. 1980. Divergence in the island night lizard XANTUSIA RIVERSIANA (Sauria: Xantusiidae). Pages 565-583 in D. M. Power, editor. The California Islands: Proceedings of a multidisciplinary symposium. Santa Barbara Natural History Museum, Santa Barbara, California.

  • Collins, J. T. 1990. Standard common and current scientific names for North American amphibians and reptiles. 3rd ed. Society for the Study of Amphibians and Reptiles. Herpetological Circular No. 19. 41 pp.

  • Crother, B. I. (editor). 2008. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. Sixth edition. Society for the Study of Amphibians and Reptiles Herpetological Circular 37:1-84. Online with updates at: http://www.ssarherps.org/pages/comm_names/Index.php

  • Crother, B. I. (editor). 2012. Scientific and standard English names of amphibians and reptiles of North America north of Mexico, with comments regarding confidence in our understanding. 7th edition. SSAR Herpetological Circular 39:1-92.

  • Crother, B. I., M. M. Miyamoto, and W. F. Presch. 1986. Phylogeny and biogeography of the lizard family Xantusiidae. Systematic Zoology 35:37-45.

  • Fellers, G. M., and C. A. Drost. 1991a. Xantusia riversiana. Catalogue of American Amphibians and Reptiles 518:1-4.

  • Fellers, G. M., and C. A. Drost. 1991b. Ecology of the island night lizard, Xantusia riversiana, on Santa Barbara Island, California. Herpetological Monographs 5:28-78.

  • Matthews, J.R. and C.J. Moseley (eds.). 1990. The Official World Wildlife Fund Guide to Endangered Species of North America. Volume 1. Plants, Mammals. xxiii + pp 1-560 + 33 pp. appendix + 6 pp. glossary + 16 pp. index. 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. 1985a. A field guide to western reptiles and amphibians. Second edition. Houghton Mifflin Company, Boston, Massachusetts. xiv + 336 pp.

  • Stebbins, R. C. 2003. A field guide to western reptiles and amphibians. Third edition. Houghton Mifflin Company, Boston.

  • U.S. Fish and Wildlife Service (USFWS ). 1980. Selected vertebrate endangered species of the seacoast of the United States- island night lizard. FWS/OBS-80/01.36, Slidell.

  • U.S. Fish and Wildlife Service (USFWS). 1990. Endangered and threatened species recovery program: report to Congress. 406 pp.

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