U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2006–3060

April 2006

Arizona Black Rattlesnake (Crotalus viridis cerberus)

Printed on recycled paper

Figure 1. Adult Arizona black rattlesnake (Crotalus viridis cerberus). 

The species is unusual because it makes use of high-altitude habitat 

and has a distinct black coloration as an adult. USGS researchers 

were the first to conduct extensive studies of this species in the wild.

 The Arizona black rattlesnake makes its home at higher 

elevations in Arizona and far western New Mexico. The snake’s 

use of high-altitude habitat and its black coloration as an adult 

distinguishes it from other subspecies of the western rattlesnake 

(Crotalus viridis), which prefer lower elevations and range from 

tan to reddish in color as adults. These physical and habitat 

differences are also reflected in genetic differences that suggest 

that the Arizona black rattlesnake may be a new species of 

rattlesnake. 

 Despite the species’s limited range, basic biological 

information needed to make management decisions is lacking 

for most Arizona black rattlesnake populations. To address this 

need, U.S. Geological Survey (USGS) scientists conducted 

research on the species in Arizona national park units from 2003 

to 2005. The research examined relative population abundance, 

movement patterns, range requirements, dietary habits, and winter 

and summer habitat. Research in Arizona national parks was 

made possible through the support of the Western National Parks 

Association, Tonto National Monument, and the USGS Science 

Internships for Workforce Diversity Program. Importantly, the 

park-based research was used to augment a long-term markrecapture study of the species that has been conducted by USGS 

biologists at sites near Flagstaff, Arizona, since 1999. USGS 

researchers were the first to conduct extensive studies of this 

species in the wild.

Research Findings

 Part of the research effort involved surveying Walnut 

Canyon National Monument, Saguaro National Park, and Tonto 

National Monument for Arizona black rattlesnakes. USGS 

biologists worked with park staff and volunteers to conduct 

walking surveys of each park unit during the primary season 

the snakes were expected to be active, late March through early 

October. The survey teams systematically searched areas that 

were suspected to be good habitat for the species and recorded 

basic statistics for each rattlesnake encountered. These efforts 

resulted in the identification of a relatively small number of 

Arizona black rattlesnakes. For this reason, it was not possible 

for scientists to determine specific population numbers for 

individual park units. In terms of relative abundance, the 

research team estimated that the species was most abundant at 

the highest elevations in Saguaro National Park, less common 

in Walnut Canyon National Monument, and rare at the lower 

elevations in Tonto National Monument. Interestingly, the 

species appears to coexist with the Hopi rattlesnake (Crotalus 

viridis nuntius), a subspecies of the western rattlesnake, at 

Walnut Canyon National Monument.

 More extensive research activities took place in Tonto 

National Monument because park managers there needed 

information about the movement patterns and behavior of 

Arizona black rattlesnakes, which were frequenting wash areas 

used by visitors. Adult Arizona black rattlesnakes captured 

in Tonto National Monument were implanted with radio 

transmitters. The transmitters allowed scientists to track the 

movements of individual snakes. This project was the first radio 

telemetry study of the species.

 USGS research indicated that Tonto National Monument, 

which is located in the upper reaches of the Sonoran Desert, 

is apparently at the lower elevation limit for the Arizona black 

rattlesnake, which tends to prefer moister and cooler habitats. 

Within the monument, the snakes made use of moist habitats 

and dense vegetation. Scientists were also able to determine 

that Arizona black rattlesnakes did not spend much time in 

developed areas like trails and visitor areas. The snakes are 

thought to travel through developed areas on their way to more 

natural areas that offer them more protection and denser cover. 

 USGS research also indicated that Arizona black 

rattlesnakes in the monument mate in late summer and fall, 

coinciding with the summer rains. Scientists also witnessed 

a male snake coil in a tight circle completely on top of a female, 

a behavior known as “stacking,” during courtship. This behavior 

had not been previously seen in Arizona black rattlesnakes. 

Another finding of interest is that female Arizona black 

rattlesnakes appear to produce four to five young. Scientists 
captured an adult female in May that was found to contain five 

ovulated eggs. The snake subsequently became pregnant and 

was presumed to have had four to five young in August. As 

is typical of other rattlesnake species, female Arizona black 

rattlesnakes appear to stay with their young until the young first 

shed their skins, approximately one to two weeks after birth. 

 The hibernation period for rattlesnakes in Tonto National 

Monument lasts from late October through March, which 

is approximately two month shorter than the hibernation 

period observed for the species near Flagstaff, Arizona. The 

hibernation sites used by the rattlesnakes observed in Tonto 

National Monument, however, were similar to those used by 

the Flagstaff-area populations and featured slopes formed by 

rocky debris.

Figure 2. Volunteers at Tonto National Monument, Arizona, helped 

conduct surveys of Arizona black rattlesnakes during the primary 

season the snakes were expected to be active, late March through 

early October. 

Research Implications

 Arizona black rattlesnakes were found to be relatively 

rare within the three Arizona national park units in which 

USGS research was conducted. Additionally, the research 

indicated that the species prefers specific habitats during both 

the summer active season and the winter hibernation season. 

This information can be used by park managers who may 

want to examine conservation strategies for the Arizona black 

rattlesnake because of its apparent rarity in the parks. For 

example, fire management plans can restrict controlled burns 

in rattlesnake habitat during the period when snakes leave their 

hibernation sites and when young are most vulnerable.

 In terms of managing possible rattlesnake-human conflicts, 

visitors could be alerted to the possibility of finding the snakes 

in certain habitats during the summer. If an Arizona black 

rattlesnake does need to be removed for safety reasons, then 

USGS research suggests that a fairly short-distance relocation of 

less than 50 m (164 ft) is preferable because of the fairly specific 

habitat needs of this rattlesnake. By better understanding 

rattlesnake behavior, park managers can not only reduce 

negative rattlesnake-human encounters, but also ensure that this 

fascinating creature has a place in Arizona national parks.

More Information

Nowak, E., and Schofer, J., 2005, Initial surveys to locate 

Arizona black rattlesnakes (Crotalus viridis cerberus) in 

Arizona national parks and monuments: Layman report (04-

14) submitted to Western National Parks Association, U.S. 

Geological Survey Colorado Plateau Research Station, 3 p.

Nowak, E., 2006, Ecology of the Arizona black rattlesnake 

(Crotalus [viridis] cerberus) at Tonto National Monument, 

Arizona: Final report submitted to Desert Southwest 

Cooperative Ecosystem Studies Unit, U.S. Geological Survey, 

Colorado Plateau Research Station, 18 p.

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

 Arizona rattlesnake 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.

Figure 3. An immature Arizona black rattlesnake at Tonto National 

Monument, Arizona. Young snakes do not exhibit the distinct black 

coloration of the species.