U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2006–3059

April 2006

Narrow-headed Garter Snake (Thamnophis rufipunctatus)

Printed on recycled paper

 The narrow-headed garter snake is a harmless, nonvenomous 

snake that is distinguished by its elongated, triangular-shaped 

head and the red or dark spots on its olive to tan body. Today, 

the narrow-headed garter snake is a species of special concern in 

the United States because of its decline over much of its historic 

range. Arizona’s Oak Creek has historically contained the 

largest population of narrow-headed garter snakes in the United 

States. The U.S. Geological Survey (USGS) and the Arizona 

Game and Fish Department jointly funded research by USGS 

scientists in Oak Creek to shed light on the factors causing 

declining population numbers. The research resulted in better 

understanding of the snake’s habitat needs, winter and summer 

range, and dietary habits. Based on the research findings, 

the U.S. Forest Service has developed recommendations that 

visitors and local residents can adopt to help slow the decline of 

the narrow-headed garter snake in Oak Creek.

Research Findings

 Narrow-headed garter snakes spend most of their lives in or 

immediately adjacent to the perennial streams of the Mogollon 

Rim and the White Mountains of Arizona and New Mexico in 

the United States and in the Sierra Madre Occidental mountain 

range in Mexico. The snakes were once common throughout 

Oak Creek, which originates north of Sedona and ends near 

Cottonwood, Arizona, at the confluence with the Verde River. 

Today, the narrow-headed garter is seldom found downstream of 

Oak Creek Canyon. USGS data indicate that current population 

numbers appear to be stable in the upper and middle reaches of 

Oak Creek Canyon; however, there is evidence of declines in 

lower canyon reaches.

 By tracking snakes that were surgically implanted with 

radio transmitters, USGS biologists were able to determine 

that narrow-headed garter snakes in Oak Creek hibernate from 

November to April in rocky areas well above the floodplain. 

This behavior probably developed as a strategy for avoiding 

winter or spring floods. The research effort also confirmed that 

the snakes have small home ranges. If fact, during the summer 

the snakes usually do not travel more than 0.8 km (0.5 mi) 

from their hibernation sites. Adult narrow-headed garter snakes 

appear to favor sections of Oak Creek Canyon with overhanging 

vegetation that provides hiding places from predators. Hawks, 

wading birds, ravens and crows, raccoons, crayfish, predatory 

fish, and other snake species will eat garter snakes. 

 Fish are a major source of food for narrow-headed garter 

snakes, which also hunt frogs and tadpoles. In Oak Creek, 

narrow-headed garter snakes appear to feed primarily on 

smooth-bodied fish with soft fins, especially nonnative brown 

(Salmo trutta) and rainbow trout (Oncorhynchus mykiss) and 

native suckers and speckled dace (Rhinichthys osculus). Native 

and nonnative fish species with this fusiform, or smooth, body 

type are more abundant in upper Oak Creek Canyon. USGS 

research findings indicate that the overall distribution pattern 

of narrow-headed garter snakes parallels the availability and 

relative abundance of smooth-bodied fish in Oak Creek. The 

lower sections of the creek are dominated by nonnative fish 

species with stiff, spiny fins, which may make them unsuitable 

prey for the snakes because they represent a choking hazard. 

More research is needed to understand the interaction of 

narrow-headed garter snakes with nonnative fish species.

Causes of Decline

 Research suggests that multiple factors are likely 

contributing to population declines for the narrow-headed garter 

snake in Oak Creek. The most significant factor appears to be 

the negative effects of nonnative crayfish on snakes and their 

prey base. Crayfish are opportunistic feeders, eating both plants 

and animals, including young snakes, and can quickly outgrow 

predation by most fish. USGS research in the Southwest 

confirms that nonnative crayfish prey on native fish species 

and compete with them for food and cover. Declines in snake 

populations may also be caused by the replacement of native 

Figure 1. Narrow-headed garter snake (Thamnophis rufipunctatus) 

is a species of special concern in the United States. The U.S. 

Geological Survey (USGS) and the Arizona Game and Fish 

Department jointly funded research by USGS scientists in Oak 

Creek to explore the factors causing population declines.
Figure 2. Narrow-headed garter snake with nonnative brown trout. 

(photograph courtesy of Susi MacVean, Arizona Game and Fish Department)

fish that the snakes feed on with nonnative species and increases 

in other nonnative fish that may prey on the snakes. Another 

contributing factor is thought to be the heavy recreational 

use of Oak Creek, which can result in the localized trampling 

of habitat used by young snakes and fish for spawning sites. 

Floods, the intentional killing or relocation of snakes by people, 

and the accidental killing of snakes by vehicles using low-water 

crossings can also result in snake mortality.

Figure 3. This adult narrow-headed garter snake was surgically 

implanted with a radio transmitter. The transmitter allowed USGS 

scientists to track the snake’s movements, providing insights into 

travel patterns and habitat needs.

Research Implications

 USGS research has identified a number of the factors 

contributing to the decline of the narrow-headed garter snake in 

Oak Creek. As with all USGS research, this effort was designed 

to develop relevant information that could inform and support 

management decisions. The U.S. Forest Service has used the 

findings to develop recommendations that visitors and local 

residents can adopt. Forest managers worked cooperatively 

with Friends of the Forest and the National Forest Foundation 

to post signs in developed areas of Oak Creek listing the 

recommendations. The signs include the following suggestions:

 • Please do not kill or relocate the garter snakes.

 • Please do not handle or collect the snakes because they 

 overheat with handling and do not adapt well to captivity.

 • Watch for young garter snakes when driving over low- 

 water crossings.

 • Keep pets leashed.

 • Stay near developed recreation sites and step on rocks 

 when enjoying the creek.

 • Do not release live bait, especially crayfish, into the creek.

More Information

Nowak, E., 2005, Monitoring surveys and radio-telemetry of 

narrow-headed garter snakes (Thamnophis rufipunctatus) in 

Oak Creek, Arizona: Draft annual progress report submitted 

to Arizona Game and Fish Department, U.S. Geological 

Survey, Colorado Plateau Research Station, 20 p.

Nowak, E.M., and Santana-Bendix, M.A., 2002, Status, 

distribution, and management recommendations for the 

narrow-headed garter snakes (Thamnophis rufipunctatus) 

in Oak Creek, Arizona: Final report submitted to Arizona 

Game and Fish Department (Heritage Grant I99007), U.S. 

Geological Survey, Colorado Plateau Research Station.

Erika M. Nowak, U.S. Geological Survey

Southwest Biological Science Center

Colorado Plateau Research Station

2255 N. Gemini Drive

Flagstaff, Arizona, 86001

Tel: 928-556-7466 (ext. 239); E-mail: enowak@usgs.gov

 Narrow-headed garter snake research is conducted by 

the Southwest Biological Science Center (SBSC) [http://sbsc.

wr.usgs.gov], which is one of the 17 science centers that are 

a part of the U.S. Geological Survey’s Biological Resources 

Discipline. To address the research needs of the large and 

biologically varied Southwestern United States, SBSC research 

is conducted by scientists working at four research stations, 

including Canyonlands Research Station (Moab, Utah), 

Colorado Plateau Research Station (Flagstaff, Arizona), Grand 

Canyon Monitoring and Research Center (Flagstaff, Arizona), 

and Sonoran Desert Research Station (Tucson, Arizona). The 

mission of the USGS Biological Resources Discipline is to 

work with others to provide the scientific understanding and 

technologies needed to support the sound management and 

conservation of the Nation’s biological resources.