In mammals, the general pattern of dispersal seems to be that males are more mobile, while females remain nearer to their natal areas.

Cougar GPS dispersal project

Dispersal patterns of subadult animals as they reach sexual maturity are an important factor determining gene flow, population genetic structure, and ultimately genetic diversity in populations. In mammals, the general pattern of dispersal seems to be that males are more mobile, while females remain nearer to their natal areas (Greenwood 1980). One of the reasons for this may be that group living mammals are primarily polygynous (Eisenberg 1981), thus subordinate males are excluded from breeding and are forced to move to other groups in order to increase their reproductive potential. In monogamous species, both females and males are excluded from breeding by a dominant pair and both sexes may need to disperse to reproduce successfully (Rood 1987).

It is generally hypothesized that dispersing animals will occupy the first unoccupied habitat they encounter (Waser 1985). However, there are instances where dispersers are tolerated within adult home ranges (McCord 1974, Anderson 1987), and other instances where dispersers travel long distances (sometimes returning later) even though suitable habitat appeared to be found nearby (Craighead 1994).

More on Cougar Disperal Project

In cooperation with the Montana Department of Fish, Wildlife, and Parks (MDFWP) and American Wildlands' Corridors of Life Project we investigated the movements of dispersing juvenile cougars in the Big Belt Mountains of central Montana.

When cougars reach about one year of age, they are weaned from their mothers and begin to live on their own.

Female offspring are tolerated by their mothers and generally remain nearby, establishing a home range adjacent and/or overlapping with their mother's. This is the general rule, but occasionally females will wander farther afield.

Male offspring, on the other hand, are forced to leave and establish a home range at a much farther distance. The reasons for this sexual difference in behavior are uncertain, but it seems to be partially a mechanism for ensuring the dispersal of genes by male movements, and avoiding inbreeding to some extent by separating young males from their mothers.

Male cougars, then, leave their mother's home range after weaning and begin traveling to find a place to live. According to Kerry Murphy, who studies cougars with the Hornocker Wildlife Research Institute, they go into a "dispersal mode" which can last several months. During this time they explore their environment, often traveling great distances and venturing into habitats that are less than perfect. At some point they decide to settle down, find a place with good habitat and little competition from resident males (if possible), and begin to establish a home range where they will spend the rest of their lives.

In order to understand this behavior better, and to relate it to protected habitat and connecting corridors, we followed the movements of dispersing juveniles using radio-telemetry. During the spring of 1996, 3 cougars were tagged with CERI radio-transmitters (built by Telonics Inc.); 2 were kittens that were close to weaning and one was a young male resident. The 2 kittens moved away from the west side of the study area with their mother during early summer and then managed to remove their collars. Since they were siblings and often played and wrestled with each other it is probable that they just chewed and tugged on each other's collar until it came loose. The collars were subsequently retrieved.

The young male (Thor) shared the west side of the study area with an older, much larger, male, and kept his distance throughout the summer. During the course of radiotracking, he crossed Holter Lake at the southern end many times. The Lake is about 1/4 mile or wider at this point. Thor spent much of the summer in a small patch of timber not far from a campground, but no campers ever seem to have known of his proximity. The large, resident male remained farther upslope and to the east. In the fall, Thor moved farther away onto a large private ranch where he was subsequently shot. The radio collar was returned in good shape. All 3 radio collars, plus 2 others provided by CERI were deployed again the following winter and spring.