The basic framework of corridor analysis consists of identifying areas of habitat which are suitable for the wildlife species in question. Habitat suitability depends upon the needs of a given species. It can be approximated by overlaying layers such as current vegetation, topography (aspect, slope, elevation), distance to water, and perhaps climatic variables such as average temperature and precipitation. Because different wildlife species vary in their sensitivity to human disturbance, habitat suitability is constrained by disturbance variables such as distance to roads, distance to towns, traffic volumes, hunting status, etc. Generally, a coverage of known distribution of a species (sightings, radio-telemetry locations, hunter-kill and road-kill sites) is also developed.

A probability contour is finally developed from the convergence of these coverages to indicate the likelihood of a given area being suitable for a given species. Where this probable habitat connects areas of known population centers, it is often termed a corridor.

Mountain Lion Corridor Pilot Project

For example, to model suitable habitat for mountain lions we initially used 1:100,000 coverages developed by the Interior Columbia Basin Ecosystem Management Project. Current vegetation coverages (structure stages and cover types) were derived from NOAA AVHRR imagery and were mapped using 1 km2 pixels. Predicted road density was derived by ICBEMP scientists using layers of management regions, lifeforms, elevation, slopes, and UPS roads using a rule-based algorhythm. These layers were reclassified, combined, and assigned a road density class for each possible combination. Streams, and lakes, were vector-based layers derived from TIGER and USGS databases. Known mountain lion distribution coverage was derived from hunting district and hunter survey data. Because mountain lion habitat suitability is strongly correlated with availability of prey species, coverages of known mule deer, elk, and mountain sheep distributions were also used.

This Pilot Project was completed using ICBEMP data during the summer of 1996. Radio-locations of dispersing cougar were used in cooperation with the Montana Department of Fish, Wildlife, and Parks to see if cougars travel within the areas we identify as probable movement corridors. This project was completed during the summer of 1997. Early results are displayed on the CERI cougar dispersal pages. Recent results and future GPS radiolocation results will be displayed on our Dispersal Study pages.

Beartooth Game Range Mountain Lion Pilot Project Area

This area, in the Big Belt Mountains, is represented using Landsat MSS imagery overlaid with a USGS streams layer. Holter Lake is located on the left side of the image with the north end of Canyon Ferry Reservoir at the bottom of the image. Juvenile lions tagged with radios in this area are likely to disperse in almost any direction.

The next step was to take a closer look at the corridor areas identified using the Montana Gap Analysis data to refine our corridor analysis.

Potential movement corridors were then mapped using 3 indices of habitat.

A simple first stage model was completed using vegetation coverages that were ranked on a scale of 1 to 4.

1) avoided habitat

2) neutral habitat

3) favorable habitat

4) preferred habitat

This model is done on a large scale using 1-square kilometer pixels. It also incorporates
Road density , and Vegetation heterogeneity ("edge").

Implicit in the model are:

However, this is only a model of habitat through which a cougar would probably move. It is not necessary to assume that the cougar could remain and find sufficient habitat to live there. It is assumed that a cougar could move through large areas of movement habitat if necessary and find prey, cover, and stalking terrain within a day or so.

A portion of these results, was done using ArcGRID to identify a Least-Cost-Path corridor for Bozeman Pass. The graphic depicted here was developed with a grizzly bear habitat model, but similar models were done for cougar and elk.

Known mountain lion distribution

Known mule deer distribution

Known elk distribution

Known bighorn sheep distribution