Winter Territoriality in Mountain Lions

1. What they did

Before this study, most of what was known about how much ground a mountain lion uses came from hunters and lion control work, and was largely guesswork. In 1964, Maurice Hornocker began a long-term study of mountain lions in the Idaho Primitive Area, a rugged wilderness in central Idaho. This paper covers the first four winters and asks how lions share space and what territoriality does for the population.

In winter, deep snow keeps lions and their prey (elk and mule deer) low down along the main streams, so the lions of the Big Creek drainage stay within a fairly small, well-defined area.

• Finding and catching lions. Each winter, from late November to late April or early May, the team searched for lions. Trained dogs were used to track and capture them. Each lion was tranquillised with a drug-filled syringe fired from a gun, marked, and released.
• Following tracks. Every set of tracks found was followed, and the team tried to capture every lion they tracked, so that the recapture data would not be biased. They also tracked known individuals to learn about their movements.
• Counting the population. Lions caught in the same area in successive years were classed as residents; those marked once and never recaptured were classed as transients. Recapture records were combined with tracks to count the lions present.
• Mapping winter ranges. For nine resident adults (four males and five females), the outermost points where each lion was caught, or tracked and then caught, were joined on a map to show its minimum winter range.

2. What they found

Captures and population

• 43 different lions were captured and marked. 31 of them were recaptured 89 times, for 132 captures in all. In total 541 days were spent searching for and tracking lions.
• About 19 lions (adults and young) were present in the winter of 1966-67 and 18 in 1967-68. Most were counted from recaptures, and a few only from their tracks.
• The population appeared to have stabilised at about 10 adults living in the area full time in winter.
• Nine resident adults, caught 59 times between them, gave most of the information on movement and territories.

Males

• Male No. 3, caught 14 times over four winters, used at least about 25 square miles.
• Male No. 18 stayed within the Rush Creek drainage.
• Male No. 7 was not caught in the last two winters, and male No. 26 was caught on the same range in both those years. The author thinks No. 26 probably replaced No. 7; the author’s data indicate that two resident males will not occupy the same range.

Females

• Female winter ranges ran from about 5 square miles (No. 29 in 1966-67) to about 20 square miles (No. 4 in 1965-66).
• A female’s range changed from year to year with her breeding status. Female No. 4, with three kittens of about 7 to 8 months, kept to the eastern part of her range. The next winter, with the same kittens now 18 to 22 months old, she was caught at the far ends of it. With new small kittens the following winter, she used only the western part. Female No. 29, alone after a year with three kittens, used only about a third of her previous range.
• Food was equally available across all ranges, so the author links these changes to the family’s growing need for food, limited at first by how far small kittens can travel.
• Resident females shared some common areas, and male ranges overlapped those of females. Neighbouring females seemed to adjust their ranges to each other without stress.
• Female No. 29 was recognised by her distinctive track, which showed she had been in the area since the study began, two years before she was first caught.

Avoidance instead of defence

• No territorial defence was seen. Transient males and females moved freely through residents’ territories. In tracking lions over literally hundreds of miles, there was no sign of one lion driving another off, and no lion showed evidence of fighting.
• From the middle of the 1965-66 winter, tracks in the snow showed that lions were avoiding close contact with one another, which the author calls a “mutual avoidance reaction”. Adult males avoided all other lions, and so did females. Lions tolerated each other only as males and females during breeding, and as mothers with dependent young.
• In one example, on 10 January 1967, a young unmarked male was caught at an elk they had killed the day before, inside the territory of resident male No. 3. Tracks showed a large male had passed within 50 yards of the young male and their kill that day. The next day the team tracked that large male, No. 3, and caught them about 3 miles away. No. 3 had made no attempt to challenge the young transient and apparently avoided the young male on purpose.
• The same areas were used by different lions, but never at the same time: lions were spaced in time as well as in space.

Scrapes

• Lions make scrape or scratch marks and urinate and often defecate on them, leaving a visual as well as a scent mark.
• All lions, but especially males, make these marks on trails, high ridges and at lion crossings, and some are permanent marking stations within each territory. Both sexes visit these sites and usually travel much the same routes.
• Several times, a lion tracked to one of these sites suddenly changed course, sometimes going back along its own trail for a long way. Each time, another lion or family of lions was found to be in the area.

3. What they concluded

• Using Etkin’s definition of territory (behaviour that keeps an animal to a particular area, without necessarily driving others out), the resident males clearly hold winter territories, but they do not defend them.
• Lions space themselves by mutual avoidance, helped by visual and scent marks, rather than by fighting. The author reached these conclusions about the scrapes before learning of similar work on domestic cats, which describes such marks working “rather like railway signals”.
• Spacing in time as well as space may also improve hunting success, because a lion hunting by stealth does better where prey has not just been disturbed by another lion.
• The main function of territoriality in this population appears to be spacing individuals out. This spacing, reached without apparent conflict, acts to limit population size, and lets the arrangement adjust to changing conditions, to other lions, and to each female’s breeding status.
• Territoriality appears very important in regulating lion numbers here, though the actual regulating mechanisms are not known.
• A solitary predator depends on its physical well-being to survive, so mutual avoidance seems to have evolved as a much more economical way of spacing than fighting. Fighting may happen at times, but the author believes it is extremely rare.

4. How tracking was or was not used

Tracking was central to the study, alongside capture and recapture:

• Trained dogs were used to track and capture the lions.
• Every set of tracks found was followed, and the team tried to capture each lion they tracked. A lion tracked and then captured counted as an “observation” when mapping winter ranges.
• Tracks were matched in time with recaptures to add to the population count; some lions in Table 2 were counted from tracks alone.
• Individual lions were recognised from their tracks: female No. 29 had a distinctive track, and tracks suggested female No. 16 was present in a winter when she was not caught.
• Snow tracking revealed the “mutual avoidance reaction”, including lions turning back at scrape sites when another lion was nearby, and the resident male who passed close to a young male at their elk kill without a challenge.
• Scrape marks with urine and scat were recorded on trails, ridges and lion crossings.

5. Tracker or observer certification

Not reported. The author did the tracking with W. Wiles, who assisted in all aspects of the field work, and with trained dogs. Nothing is said about their tracking experience or skill, although the population counts, individual identifications and avoidance findings rest partly on reading tracks in snow.

6. Other technologies, skills or innovations

• Trained dogs to track and capture lions.
• Chemical immobilisation: Sernylan (phencyclidine hydrochloride) injected into the muscle with Cap-Chur syringes fired from a specially designed powder-charge gun; 71 doses, averaging 1 mg of drug per 1.71 lbs of body weight.
• Individual marking of every lion caught, allowing recaptures over four winters.

7. Implications for conservation (from the paper)

• Territoriality, through mutual avoidance, appears to limit the number of mountain lions in an area, keeping the population fairly stable without fighting.
• Such a mechanism appears necessary for the survival of populations of solitary, specialised predators.