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BC Conservation Data Centre: Conservation Status Report

Hypsiglena chlorophaea
Desert Nightsnake

 
Scientific Name: Hypsiglena chlorophaea
Scientific Name Synonyms: Hypsiglena torquata
English Name: Desert Nightsnake
   
Provincial Status Summary
Status: S2
Date Status Assigned: March 30, 2018
Date Last Reviewed: March 24, 2025
Reasons: This species occurs within a small range in the warm dry valley bottoms of the southern Okanagan and Similkameen valleys. There have been less than 100 observations of individuals since first reported in BC in 1980. Primary threats include road mortality and habitat loss from urban development.
 
Range
Range Extent: C = 250-1,000 square km
Range Extent Estimate (km2): 853
Range Extent Comments: Desert Nightsnake is found in the lower Similkameen and South Okanagan Valleys from Keremeos in the west, Penticton in the north, and the Canada ? U.S. border south of Osoyoos in the south (Southern Interior Reptile and Amphibian Recovery Team 2008, 2016;COSEWIC 2011i). The BC CDC estimated the range extent to be 853 square km (calculated using convex hull range extent using occurrence mapped as of January 2017). This has not changed as of 2024. The two iNaturalist records (iNaturalist; accessed 1 January 2025) fall within the estimated range extent.
Area of Occupancy (km2): E = 26-125
Area of Occupancy Comments: Area of occupancy was previously (2017) estimated as 108 km2 (27 2x2 km grid cells). There have been 77 observations of this species up until 2024 (M. Sarell, pers. comm. 2024). Nightsnakes likely remain within one kilometre of their hibernacula throughout the seasons. (Hammerson 2004).
 
Occurrences & Population
Number of Occurrences: BC = 6 - 80
Comments: The BC Conservation Data Centre has 16 element occurrences mapped as of 2025; however, this is likely an underestimate as this species is very secretive and nocturnal.
Number of Occurrences with Good Viability / Ecological Integrity: BC = 1 - 12
Comments: From (Sarell 2005b): There are seven subpopulations that likely will be viable for at least 20 years, due to their remoteness from developable lands. This is despite the fact that eight known or suspected hibernacula occur on conservation holdings and another three on Indian Reserves. The viability of some of these subpopulations is tenuous due to existing or potential land uses in the vicinity of the hibernacula that create threats to individuals within their suspected summer range. Subpopulations are probably contiguous although data supporting this is in a very discreet portion of their range.
Number of Occurrences Appropriately Protected & Managed: CD = 4 - 40
Comments: From Southern Interior Reptile and Amphibian Working Group. 2016d:"Eight of the known sites are on conservation lands (e.g., lands owned by The Nature Trust of British Columbia, Vaseux Bighorn National Wildlife Area, Haynes? Lease Ecological Reserve, McTaggart-Cowan/nsk?niw?t Wildlife Management Area). One wildlife habitat area (336 ha) for other snake species was established under the Forest and Range Practices Act Identified Wildlife Management Strategy (IWMS) and will benefit Desert Nightsnake since they use similar habitats. Desert Nightsnake is not listed as an Identified Wildlife Species. Private land conservancies have protected habitat: The Nature Trust of British Columbia?s Okanagan Falls Biodiversity Ranch, Skaha Eastside, Emery, and Antelope-brush properties, Southern Interior Land Trust S.L.15)."
Population Size: C = 250 - 1,000 individuals
Comments: "These snakes are secretive, nocturnal, and patchily distributed in the landscape; all these factors make them difficult to detect and study. However, apart from issues with detection, their densities appear to be extremely low as evidenced by relatively few additional records despite increased search effort." (COSEWIC 2011i)

2024: 77 observations (M. Sarell, pers. comm. 2024); 2011: 72 confirmed observations (COSEWIC 2011i; Southern Interior Reptile and Amphibian Working Group. 2016d); 2010: 62 confirmed observations (M. Sarell, pers. comm. 2010). 2005: 30 confirmed observations have been made since they were first discovered in 1980 (Sarell 2005b).
 
Threats (to population, occurrences, or area affected)
Degree of Threat: B = High
Comments: 2018: The overall threat impact for this species is High. Primary threats include direct harm from road mortality and habitat loss from housing and urban development. Lower-ranked threats include habitat loss or degradation from agriculture, quarrying, and fire suppression, and direct harm from invasive non-native species. (Southern Interior Reptile and Amphibian Working Group 2016d). These threats remain the highest (ECCC 2019e).

2011: This species is threatened by loss of habitat because of agriculture and urban development and road mortality. Talus removal for construction, landscape rocks and rip-rap is also a threat (Gregory, in press; Sarell et al. 2004). Direct persecution may sometimes occur because of similarity to young rattlesnakes (Bufo Incorporated 1993). An increasing threat from predation by pets is anticipated as residential development expands into Night Snake habitat.
 
Trend (in population, range, area occupied, and/or condition of occurrences)
Short-Term Trend: U = Unknown
Comments: Trends are unknown; Nightsnakes are cryptic in nature and very few individuals have been found. There has likely been a decline; however, this should be verified.
Long-Term Trend: U = Unknown
 
Other Factors
Intrinsic Vulnerability: B=Moderately vulnerable
Comments: Nightsnakes likely do not move far from their hibernacula during the active season. While this affords them some protection from traffic and pets, it limits their ability to maintain metapopulation connectivity with other colonies, thus inhibiting gene exchange and decreasing the reproductive capacity and fitness of these populations. Isolated populations likely will not persist.
Environmental Specificity: BC=Narrow to moderate.
Comments: Nightsnakes are known to be dependent on rocky slopes but they are also known to occur in other ecosystems types.
Other Rank Considerations: Significant knowledge gaps in life history, range, and habitat preferences limit the ability to fully assess the vulnerability of this species.
 
Information Gaps
Research Needs: Very little is known about Nightsnake populations or habitat use throughout their range. This is crucial to establishing viable population estimates and effective conservation targets.
Inventory Needs: Continued inventories are needed within the Nightsnake's range; a variety of techniques should be used. Surveys outside the known range are needed to refine range extent. Naturalists, field biologists, and landowners with suitable habitat in the south Okanagan and lower Similkameen should be made aware of this species to increase their awareness and encourage sighting reports.
 
Stewardship
Protection:
Management:
 
Version
Author: Ramsay, L. (2025), L. Gelling (2011, 2018), L. Westereng (2007), Sarell, M.J. (2005)
Date: January 01, 2025
 
References
Bezener, A.M., M. Dunn, O. Dyer, R. Hawes, T. Hayes, H. Richardson, and B. White. 2004. Draft recovery strategy for species at risk in the South Okanagan and Lower Similkameen Valleys of British Columbia, Canada: towards integrating the landscape-level and single-species approaches to conservation. South Okanagan-Similkameen Conserv. Program, Penticton, BC.
Bufo Incorporated. 1993. Report on the status of the night snake (Hypsiglena torquata) in British Columbia. Unpubl. rep. submitted to Wildl. Branch, B.C. Minist. Environ., Lands and Parks. 38pp.
COSEWIC 2001h. COSEWIC assessment and status report on the night snake Hypsiglena torquata in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 25 pp.
COSEWIC. 2011g. COSEWIC status appraisal summary on the Desert Nightsnake Hypsiglena chlorophaea in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xiii pp.
Diller, L.V., and R.L. Wallace. 1986. Aspects of the life history and ecology of the desert night snake, Hypsiglena torquata deserticola: Colubridae, in southwestern Idaho. Southwest. Nat. 31(1):55-64.
Engelstoft, C. 2004. Sharp-tailed Snake habitat assessment and survey on Coast Guard, DND and Parks Canada properties in the Capital Region, BC. Report prepared for Parks Canada.
Engelstoft, C., K. Ovaska, and N. Honkanen. 1999. The harmonic direction finder: a new method for tracking movements of small snakes. Herpetological Review. 30(2):84-87.
Gregory, L. 2005. COSEWIC status report on the night snake Hypsiglena torquata in Canada. in COSEWIC assessment and status report on the night snake Hypsiglena torquata in Canada. Comm. on the Status of Endangered Wildl. in Can.. Ottawa. 25pp. In press.
Hammerson, G. 2004. Population/Occurrence Delineation for Small Colubrid Snakes. In NatureServe Explorer: An online encyclopedia of life [web application]. NatureServe, Arlington, VA. Online. Available: http://www.natureserve.org/explorer. Accessed February 20, 2005.
Hammerson, G.A. 1982. Amphibians and reptiles in Colorado. Colorado Div. Wildl., Denver. vii+131pp.
iNaturalist community. 2025f. Observations of Hypsiglena chlorophaea from British Columbia, Canada. Exported from www.inaturalist.org on 1 January 2025.
Lacey, H., C.H. Shewchuck, P.T. Gregory, M.J. Sarell, and L.P. Gregory. 1996. The occurrence of the Night Snake, Hypsiglena torquata, in British Columbia, with comments on its bodysize and diet. Can. Field-Nat. 110:620-625.
Nussbaum, R.A., E.D. Brodie Jr., and R.M. Storm. 1983. Amphibians and Reptiles of the Pacific Northwest. Univ. Press of Idaho. 332pp.
Radke, W.R. 1989. Memorandum: Ecology of the Northern Pacific Rattlesnake on Columbia NWR - 1989 Progress Report. U.S. Fish and Wildl. Serv., Othello, WA. 3pp.
Sarell, M. 2005a. Description of residence for the Desert Night Snake (Hypsiglena torquata deserticola). Prepared for Can. Wildl. Serv., Delta, BC.
Sarell, M. 2005b. Unpublished georeferenced observations of the Desert Night Snake (Hypsiglena torquata deserticola) in British Columbia. Excel 2000 database.
Sarell, M. 2005c. In Progress. Night Snake (Hypsiglena torquata) in Standards for Managing Identified Wildlife: Accounts, Volume 3. Biodiversity Branch, B.C. Minist. Water, Land, and Air Prot., Victoria.
Sarell, M.J., D. Nield, and B.C. Southern Interior Reptile and Amphibian Recovery Team. 2004. Recovery plan for the Desert Night Snake (Hypsiglena torquata) in Canada. National Recovery Plan No. X. Recovery of Nationally Endangered Wildlife (RENEW), Ottawa.
Southern Interior Reptile and Amphibian Working Group. 2016d. Recovery plan for the Desert Nightsnake (Hypsiglena chlorophaea) in British Columbia. Prepared for the B.C. Ministry of Environment, Victoria, BC. 28 pp.
 
Spalding, D.J. 1995. The Sharptail Snake: a British Columbia rarity. Cordillera. 2:20-25.
Stebbins, R.C. 1985. A field guide to western reptiles and amphibians. Second ed. Houghton Mifflin Co., Boston, MA. xiv+336pp.
Wood, C. 2003. GIS mapping of antelope brush in the South Okanagan Similkameen. Prepared for Minist. Water, Land and Air Prot., Penticton, BC. 6pp.
 

Please visit the website Conservation Status Ranks for information on how the CDC determines conservation status ranks. For global conservation status reports and ranks, please visit the NatureServe website http://www.natureserve.org/.

Suggested Citation:

B.C. Conservation Data Centre. 2025. Conservation Status Report: Hypsiglena chlorophaea. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 9, 2026).