U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2005–3102

September 2005

In cooperation with the Colorado Division of Wildlife, Bureau of Land Management, U.S. Forest Service, and National Park Service

Roads and Traffic: Effects on Ecology and Wildlife Habitat Use 

Applications for Cooperative Adaptive Management

Printed on recycled paper

Vehicles in Wildlife Habitat

The land of the United States is dissected 

by more than 4 million miles of roads that 

fragment wildlife habitat on both public and 

private lands. Traffic on these roads causes 

additional effects. On secondary roads, which 

provide access to the most natural habitat, the 

levels, timing, and types of traffic are seldom 

known. In order to understand the effects 

of traffic on wildlife, USGS is conducting 

research cooperatively with the Bureau of 

Land Management, the U.S. Forest Service, 

the National Park Service, and the Colorado 

Division of Wildlife.

Simultaneous Observations of

Traffic and Wildlife

The key to understanding the effects of 

traffic on wildlife is to observe traffic and 

wildlife simultaneously. Several traffic monitoring technologies permit the observation 

of vehicles; the most common is the familiar 

pneumatic counter with hoses stretched across 

the road. This type of counter registers time of

vehicle crossing, speed, wheelbase, and number of axles. This information allows USGS 

scientists to separately count full size vehicles, 

vehicles towing trailers, off highway vehicles 

(OHVs), and trucks that may be used in 

extractive operations such as logging. Vehicles 

can also be counted using magnetometers 

and other sensors, but because these devices 

do not deliver information about vehicle type 

and speed, scientists use them only for special 

applications, where pneumatic counters are 

impractical.

Global Positioning System (GPS) instruments are now available for wildlife monitoring. GPS collars for medium and large animals operate for months or years, internally 

storing data on positions and times. Data from 

the collars can be downloaded over a radio 

link, so scientists can learn how animals are 

moving while the collars remain in place to 

collect more positions. Expected advances in 

miniaturization will soon permit GPS tracking 

of medium-size birds such as sage grouse.

With simultaneous application of these 

technologies, researchers can determine traffic 

effects on selected species. Analysis of traffic 

and animal movement is done over multiple 

time scales because some animals may not 

respond immediately to traffic, but instead 

may respond to longer term changes in average traffic levels or in types of vehicles.

Gunnison Basin Studies

The Gunnison Basin of western Colorado 

has two important species that may be disturbed by traffic, with attendant management 

consequences: elk (Cervus elaphus) and Gunnison sage grouse (Centrocercus minimus). 

Elk Movement and Vehicles 

Elk migrating between summer range on 

Black Mesa and in the West Elk Mountains, 

and winter range along the northeast rim of 

the Black Canyon of the Gunnison, have an 

increasing population. A working hypothesis advanced by the Colorado Division of 

Wildlife is that late summer OHV traffic on 

Gunnison National Forest fosters early movement of the herd to its winter range. There, 

in Black Canyon of the Gunnison National 

Park and on nearby private land, the herd finds 

refuge from hunting with the result that elk 

populations cannot be managed effectively. 

The large numbers of grazing elk compete 

with cattle for fodder on private lands, and on 

public lands they move through sensitive sage 

grouse habitat.

USGS is collecting its second season 

of vehicle data along the elk migration 

route, and in late 2005 will place collars on 

approxi­mate­ly 20 elk. Later placement of 

an additional 30 collars will bring the total 

count to 50, a number sufficient for definitive 

study. After two to three years of observation, 

as GPS locations continue to be acquired, 

answers should emerge as to the extent that 

vehicles influence the timing of elk movement. If managers make changes in their traffic 

policies, then continued observations will 

determine whether management changes are 

having the desired effect.

Gunnison Basin Cooperative Study Area

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Human Impacts on Sage Grouse 

Habitat Use and Movements

Sage grouse exhibit elaborate mating 

rituals at courting sites known as leks. Bird 

watchers and other members of the public 

understandably want to observe these 

behaviors, but it has long been observed that 

grouse abandon their leks, and therefore their 

breeding activity, when disturbed by humans. 

Breeding may also be disturbed by large 

animals, such as elk and cattle. 

Breeding success is particularly important 

for the Gunnison grouse; in 2000 its 

population was estimated at 4000 birds, less 

than 1% of the 1950 estimated population, 

and its range is now fragmented into 8 

distinct areas. Roads may be a factor in the 

Gunnison Sage grouse population decline, for 

a number of reasons including disturbance 

by vehicles and increased vulnerability to 

predators. Power lines are often associated 

with roads and add risk by providing perches 

for predators.

During the spring of 2005, USGS 

monitored motorized vehicle use on a network

of roads that give access to Gunnison sage 

grouse leks. This was the first monitoring 

program that provided local land managers 

with definitive, quantitative information 

about the number of vehicles present during 

the breeding season. Scientists from the 

cooperating agencies and from Western State 

College have been planning an augmented 

observation program involving GPS tracking 

of cattle in order to better understand 

possible disturbance of grouse breeding by 

livestock. Quantitative disturbance data will 

provide a basis for consideration of adaptive 

management options, including restriction 

of grazing during the grouse breeding and 

rearing seasons of spring and early summer. 

Long Term Monitoring of Sage Grouse 

Habitat

Habitat responds constantly to weather, 

land use, invasive species, and other factors. 

Traffic disturbance occurs against this changing background, so USGS and BLM have 

designed a habitat monitoring program, using 

high resolution satellite imagery, as a companion to traffic and grouse monitoring. These 

These graphs illustrate summary traffic data for two roads in the Gunnison Basin. Corral Gulch Road gives access to a logging 

lease on Gunnison National Forest, and has higher traffic levels (and larger vehicles) during the week. Crystal Main Road 

is similar but used primarily for recreation; it has higher traffic levels on weekends. Higher speeds and traffic levels on the 

recreational road may imply higher risk of vehicle-animal collisions.

observations will document changes in the 

road network, general type of vegetation, and 

vegetation canopy. Observations are planned 

four times per year for thirty years. 

Contact Information

Douglas S. Ouren

Phone: 970-226-9476

E-mail: doug_ouren@usgs.gov

Raymond D. Watts

Phone: 970-226-9378

E-mail: rwatts@usgs.gov

USGS Fort Collins Science Center

2150 Centre Ave Bldg C

Fort Collins CO 80526-8118

Web: http://www.fort.usgs.gov