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Lower Colorado River Multi-Species Conservation Program Balancing Resource Use and Conservation

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Northern Mexican Gartersnake

      (Thamnophis eques megalops)

First northern Mexican gartersnake found on the Colorado River since 1904.  It was discovered at Beal Lake Conservation Area in April 2015. - Photo by Great Basin Bird ObservatoryA northern Mexican gartersnake found during surveys along the Big Sandy River in Arizona - Photo by Jeneal Smith, ReclamationA northern Mexican gartersnake found during surveys along the Big Sandy River in Arizona - Photo by Jeneal Smith, Reclamation

General Description

The northern Mexican gartersnake is a subspecies of the Mexican gartersnake (Thamnophis eques). The northern Mexican gartersnake is very similar to the Mexican gartersnake in both size and coloration. The Mexican gartersnake averages between 45 centimeters (18 inches) to 101 centimeters (40 inches) in total length, and can reach lengths up to 112 centimeters (44 inches). The coloration of the northern Mexican gartersnake ranges from olive to olive-brown to olive-gray with three stripes that run the length of the body. The middle dorsal stripe is a creamy yellow and darkens toward the tail. The pale yellow to light-tan lateral stripes distinguish the northern Mexican gartersnake from other sympatric (co-occurring) gartersnake species because a portion of the lateral stripe is found on the fourth scale row, while it is confined to lower scale rows for other species.

Legal Status

In July 2014, the northern Mexican gartersnake was listed as a threatened species under the Endangered Species Act by the U.S. Fish and Wildlife Service (USFWS). The USFWS also proposed designation of critical habitat for this species in July 2013.

The northern Mexican gartersnake is designated as wildlife of special concern in Arizona, a State endangered species in New Mexico, and a threatened species in Mexico. The northern Mexican gartersnake was identified as a species of greatest conservation need in the Comprehensive Wildlife Conservation Strategy for New Mexico.


The northern Mexican gartersnake is a subspecies of the Mexican gartersnake. The Mexican gartersnake is a member of the family Colubridae and subfamily Natricinae.


One study found that within populations of northern Mexican gartersnake, follicular enlargement and high levels of activity were present in the fall, suggesting a fall mating period in which sperm is stored in the females until spring ovulation. It is also thought that exact time of breeding events vary with elevation. Clutch size can range anywhere from 8 to 26 young.


In Arizona and New Mexico, northern Mexican gartersnakes were found feeding primarily upon leopard frogs, the woodhouse toad, tree frogs, Gila and roundtail chubs, earthworms, and other small fish such as the Gila topminnow, desert pupfish, and longfin dace. The northern Mexican gartersnake are also known to consume tadpoles of the American bullfrog, green sunfish, bluegill, and other non-native soft-rayed fish such as mosquito fish, largemouth bass, and red shiner. It is likely northern Mexican gartersnakes will consume any native amphibian that is available within their habitat.


The northern Mexican gartersnake has declined throughout its range due to habitat alteration, habitat loss, dewatering, sedimentation, poor water clarity, reduction in streamside vegetation, non-native species replacing native species, disease, and pollution of streams, wetlands, and riparian areas. In addition to habitat degradation, the northern Mexican gartersnake has several potential predators including birds of prey, raccoons, coyotes, foxes, spiny softshell turtles, and larger snake species.

More Information

Additional information on this species, as well as source documentation, can be found in the species accounts located at this link (PDF).

Updated January 7, 2020

The northern Mexican gartersnake historically occurred in the United States and Mexico along the Sierra Madre Occidental, in the Chihuahuan Desert, and north of the Mexico Plateau in the States of Arizona, New Mexico, Sonora, Chihuahua, Durango, Guanajuato, Hidalgo, and San Luis Potosi. Its range was from central Arizona and the Gila River in New Mexico, southward to the Sierra Madre Occidental to Guanajuato, and eastward across the Mexican Plateau to Hidalgo, with an apparently isolated population in central Nuevo Leon.

There was one historical record of northern Mexican gartersnakes in the early 1900s in Nevada along the lower Colorado River (LCR). There are no historical records for California, but they could have occurred on the California side of the LCR.

The only areas within the United States with current viable populations of the northern Mexican gartersnake are located in Arizona, including the Page Springs and Bubbling Ponds Fish Hatcheries along Oak Creek, the lower Tonto Creek, the upper Santa Cruz River in the San Rafael Valley, the Bill Williams River, and the upper and middle Verde River. Throughout the rest of its historical range, the northern Mexican gartersnake is either extirpated or exists in low numbers that do not comprise viable populations.

The northern Mexican gartersnake takes advantage of any area that provides for shelter, including herbaceous vegetation, dense brush, emergent vegetation, holes, root crevices, clusters, and manmade objects. It often inhabits cienegas (mid-elevation wetlands with highly organic, reducing [basic or alkaline] soils), streams, backwaters, lakes, seeps, pools, rivers, riparian woodlands, springs, and ponds with thick bank vegetation.

LCR MSCP Conservation Measures

The Habitat Conservation Plan (HCP) provides conservation measures specific to each species. Listed below are the species specific conservation measures for the flat-tailed horned lizard. Click on the arrows to expand the table.

NMGS1—Create 1,496 acres of northern Mexican gartersnake habitat

Create and manage 512 acres of marsh to provide northern Mexican gartersnake habitat. This created habitat will also be habitat for the Yuma clapper rail (conservation measure CLRA1). Of the 5,940 acres of LCR MSCP created cottonwood-willow I-IV, 984 acres will be created and managed near to marshes to provide northern Mexican gartersnake habitat. Additional northern Mexican gartersnake habitat may be provided by marsh vegetation that becomes established along margins of the 360 acres of backwaters that will be created. These small patches of habitat may provide linkages between existing habitat and may facilitate the colonization of created habitats. Marsh associated with backwaters that are disconnected from the LCR channel are of higher value to northern Mexican gartersnake than connected backwaters on the LCR and are the preferred type to achieve LCR MSCP conservation goals for this species. Marsh associated with disconnected backwaters are managed to limit non-native predatory species, to the extent practicable. The design and management criteria described in the conservation measures for Yuma clapper rail (HCP Section 5.7.1), California black rail (HCP Section 5.7.13), southwestern willow flycatcher (HCP Section 5.7.2) and yellow-billed cuckoo (HCP Section 5.7 .14) will ensure that created cottonwood-willow and marsh areas will also provide other habitat requirements for this species.

NMGS2—Implement conservation measures to avoid or minimize take of northern Mexican gartersnakes

Implement measures to avoid or minimize take of northern Mexican gartersnakes. These measures could include worker education programs and other practices in accordance with LCR MSCP best management practices.

MRM3—Monitor and adaptively manage created covered and evaluation species habitats

Created species habitats will be managed to maintain their functions as species habitat over the term of the LCR MSCP. Created habitat will be monitored and adaptively managed over time to determine the types and frequency of management activities that may be required to maintain created cottonwood-willow, honey mesquite, marsh, and backwater land cover as habitat for covered species. This conservation measure applies to those species for which comparable measures are not subsumed under species-specific conservation measures (Section 5.7 in the HCP). They are not applicable to species for which habitat would not be created under the LCR MSCP Conservation Plan, such as the desert tortoise, relict leopard frog, humpback chub, and threecorner milkvetch.

AMM1—To the extent practicable, avoid and minimize impacts of implementing the LCR MSCP on existing covered species habitats

To the extent practicable, establishment and management of LCR MSCP–created habitats will avoid removal of existing cottonwood-willow stands, honey mesquite bosques, marsh, and backwaters to avoid and minimize impacts on habitat they provide for covered species. Temporary disturbance of covered species habitats, however, may be associated with habitat creation and subsequent maintenance activities (e.g., controlled burning in marshes and removal of trees to maintain succession objectives). LCR MSCP conservation measures that could result in such temporary disturbances will, to the extent practicable, be designed and implemented to avoid or minimize the potential for disturbance. In addition to implementing AMM3 and AMM4 below, these measures could include conducting preconstruction surveys to determine if covered species are present and, if present, implementing habitat establishment and management activities during periods when the species would be least sensitive to those activities; or redesigning the activities to avoid the need to disturb sensitive habitat use areas; staging construction activities away from sensitive habitat use areas; and implementing BMPs to control erosion when implementing ground disturbing activities.

AMM2—Avoid impacts of flow-related covered activities on covered species habitats at Topock Marsh

Impacts on groundwater levels that support covered species habitat at Topock Marsh will be avoided by maintaining water deliveries for maintenance of water levels and existing conditions. At times, flow-related activities could lower river elevations to levels that could disrupt diversion of water from the river to the marsh. Improvements to intake structures that allow water to continue to be diverted or other measures to maintain the water surface elevation will avoid effects on groundwater elevation. Avoidance of effects could be accomplished with the purchase, installation, and operation of two electric pumps sized to the current inflow at the Topock Marsh diversion inlet. The pumps would most likely need to be operated during summer to make up for the lower flow periods.

Implementation of this conservation measure would maintain existing habitat at Topock Marsh for the Yuma clapper rail, southwestern willow flycatcher, Colorado River cotton rat, western least bittern, California black rail, yellow-billed cuckoo, gilded flicker, vermilion flycatcher, Arizona Bell's vireo, and Sonoran yellow warbler. The extent of covered species habitat impacts that will be avoided by maintaining water deliveries to Topock Marsh are presented in Table 4-2 in the HCP. Maintaining water deliveries to Topock Marsh will also maintain razorback sucker and bonytail habitat associated with disconnected backwaters managed for these species.

AMM4—Minimize contaminant loads in runoff and return irrigation flows from LCR MSCP created habitats to the LCR

LCR MSCP–created habitats that require irrigation to establish and maintain vegetation to provide habitat will be designed and managed to minimize contaminant loads that could return to the LCR as runoff or return flow. Measures will include vegetation establishment methods that minimize the need for application of herbicides, pesticides, and fertilizers and designing irrigation methods and new irrigation infrastructure to reduce runoff and return-flows to the extent practicable. Use of pesticides is not a covered activity. Pesticides used to establish and maintain LCR MSCP habitats, however, will be applied in accordance with EPA restrictions and, as needed, authorization for their use will be sought under separate permits.

AMM5—Avoid impacts of operation, maintenance, and replacement of hydroelectric generation and transmission facilities on covered species in the LCR MSCP planning area

To the extent practicable, before implementing activities associated with OM&R of hydroelectric generation and transmission facilities, measures will be identified and implemented that are necessary to avoid take of covered species where such activities could otherwise result in take. These measures could include conducting surveys to determine if covered species are present and, if so, deferring the implementation of activities to avoid disturbance during the breeding season; redesigning the activities to avoid the need to disturb covered species habitat use areas; staging of equipment outside of covered species habitats; delineating the limits of vegetation control activities to ensure that only the vegetation that needs to be removed to maintain infrastructure is removed; stockpiling and disposing of removed vegetation in a manner that minimizes the risk of fire; and implementing BMPs to control erosion when implementing ground disturbing activities.

AMM6—Avoid or minimize impacts on covered species habitats during dredging, bank stabilization activities and other river management activities

To the extent practicable, before initiating activities involved with river maintenance projects, measures will be identified and implemented that avoid or minimize take of covered species where such activities could otherwise result in take. Such measures could include alternative methods to achieve project goals, timing of activities, pre-activity surveys, and minimizing the area of effect, including offsite direct and indirect effects (e.g., avoiding or minimizing the need to place dredge spoil and discharge lines in covered species habitats; placing dredge spoils in a manner that will not affect covered species habitats).

CMM1—Reduce risk of loss of created habitat to wildfire

Management of LCR MSCP conservation areas will include contributing to and integrating with local, state, and Federal agency fire management plans. Conservation areas will be designed to contain wildfire and facilitate rapid response to suppress fires (e.g., fire management plans will be an element of each conservation area management plan).

CMM2—Replace created habitat affected by wildfire

In the event of created-habitat degradation or loss as a result of wildfire, land management and habitat creation measures to support the reestablishment of native vegetation will be identified and implemented.

The Arizona Game and Fish Department (AGFD) and New Mexico Department of Game and Fish (NMDGF) have developed conservation and mitigation programs for the northern Mexican gartersnake. Captive propagation has been experimented with limited success.

The following actions assist in the conservation of the northern Mexican gartersnake:

  1. Propagation and restocking of northern Mexican gartersnake populations
  2. Removal of non-native fish and bullfrogs within currently occupied and potential habitat
  3. Prevention of the transport of non-native aquatic species
  4. Restoration of natural streamflow
  5. Protection and restoration of currently occupied and potential habitat
  6. Reduction of overgrazing
  7. Restoration and conservation of populations of native prey species
  8. Prevention of the spread of non-native aquatic species
  9. Creating education materials to reduce the deliberate or unintentional killing of northern Mexican gartersnakes
  10. Better management of live bait collection
  11. Quick restocking of native species to chemically renovated aquatic areas
  12. Removing or preventing the buildup of excessive sediment

Research and Monitoring Activities

LCR MSCP conduct a variety of research and monitoring activities along the LCR encompassing both MSCP and non-MSCP species. For a complete list of all activities, please see the Research and Monitoring Activities web page.

This gallery includes photos of this species. If you require larger photos, please contact our webmaster Michelle Reilly at mreilly@usbr.gov.

First northern Mexican gartersnake found on the Colorado River since 1904.  It was discovered at Beal Lake Conservation Area in April 2015. - Photo by Great Basin Bird Observatory A northern Mexican gartersnake found during surveys along the Big Sandy River in Arizona - Photo by Jeneal Smith, Reclamation A northern Mexican gartersnake found during surveys along the Big Sandy River in Arizona - Photo by Jeneal Smith, Reclamation