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By Winston Vickers on March 27, 2017

For 16 years, veterinarians with the Karen C. Drayer Wildlife Health Center at UC Davis have conducted research on mountain lions in Southern, and more recently with the Institute for Wildlife Studies in Northeastern, California, to monitor the lions’ habitat use, prey animals, health and disease, and human interactions.

Using cage traps with road-killed deer for bait, the researchers capture and sedate the cats, and take blood, DNA,  fecal, and other samples while checking or applying GPS collars. They have placed GPS collars (and one VHS collar) on 89 lions to date. They have also analyzed data from three additional animals collared as part of another study, collected DNA samples from more than 150 live and deceased lions, and analyzed lion mortality records going back 30 years.

Here’s what the studies tell us so far about our feline neighbors:

1. Collisions with vehicles during road crossings are the number one cause of death of GPS-collared mountain lions in the study.

Aerial view of Southern California roads and urbanized habitat
Urban development reaches into mountain lion habitat in Southern California. (Kit_Leong/Getty Images)

To establish and circulate in their territories and find mates, mountain lions must travel long distances, causing them to have to cross busy freeways or other busy roads commonly. Several specific highway sections have been identified by the researchers as hotspots of crossing and risk to the lions. As a result of this research, a $10 million fencing project was completed in Orange County by the Foothill/East Toll Road agency, and roadkill of all species in the fenced section has dropped to almost zero.

Male mountain lions have home ranges of 145 square miles on average, and females approximately half that.

2. Mountain lions are exposed to a variety of infectious diseases, and certain viruses can move between mountain lions, bobcats and domestic cats.

An orange domestic cat walks through an urban landscape
Domestic and wild felines can share disease where they interact in urban habitat. (RadulePerisic/Getty Images) 

The research team and collaborators at Colorado State University have documented that the bobcat strain of the Feline Immunodeficiency Virus (FIV) has infected some lions in Southern California, with unknown impacts so far. Other diseases have caused the death of several GPS-collared lions in the study, and one small epidemic may have occurred. Disease is a greater concern when lions are genetically isolated as in the Santa Ana Mountains, and could potentially contribute to future decline in that population.

3. Certain poisons meant to kill rodents, called anti-coagulant rodenticides, end up in the tissues of mountain lions. 

Containers of rat poison demonstrate one threat to lion
Poisons, like these rodenticides, harm lions. (Mourad Gabriel/UC Davis Integral Ecology Research Center)

These poisons can reach levels that are fatal to the lions. The researchers are trying to determine how the compounds get there since mountain lions rarely eat rodents directly. However, since lions eat animals such as coyotes, that do eat rodents, the lions may be getting poisoned that way. As a result of this work and that of others, some of the poisons that are most likely to harm wildlife have been taken off the market.

4. Mountain lions often die if they kill domestic animals, like sheep and goats.

These deaths of both lions and domestics are preventable with proper animal husbandry — that is, bringing domestic animals into protective structures at night.

Goats in an enclosure as an example of lion prey and animal husbandry
Use of livestock enclosures keeps both goats and lions from being killed. (Gregory Urquiaga/UC Davis)

Deaths secondary to depredation permits issued due to killing of a domestic animal were the second leading cause of death overall in Southern California, the number one cause of death for lions east of I-15, and the only cause of death so far for lions in the Northeastern California study. The study team has, and continues to, work with collaborators on education of animal owners about proper animal husbandry practices and testing of devices intended to deter predators from livestock enclosures.

5. Mountain lions are active from shortly before dusk to shortly after dawn.

A highway scene at dusk, when lions are more active.
Watch the road for lions crossing at times when the animals are most active. (Gregory Urquiaga/UC Davis)

These are the times that they are most likely to be using roads and trails that people also use.

6. Not only is crossing of the I-15 freeway in Southern California rare, but successful breeding and survival of mountain lions that cross the freeway and their offspring is also rare.

Lion and two cubs crossing under a freeway overpass
One occurrence of connectivity and rearing was caught on film, from which this shot was taken. (UC Davis)

As a result of the I-15 barrier, mountain lions in the Santa Ana Mountains are severely genetically restricted, with the resulting danger of inbreeding-related reproductive and physical problems. Pedigree analyses completed recently indicate that only one animal that has been detected as having crossed I-15 east to west during the study period has definitely reproduced, and he and half of his offspring are deceased. Other freeways in the region may also be barriers, and this is under investigation with our collaborators at the University of Wyoming, Dr.'s Holly Ernest, Kyle Gustafson, and Erik Gagne.

A Population Viability Analysis is underway for the Santa Ana Mountains population to determine their risk of extinction if nothing is done to improve their connectivity.

The research findings have been communicated to decision-makers to be certain that they are informed about the potential negative impact of proposed developments on the Santa Ana Mountains lions.

7. Deer are the mountain lion’s preferred prey, but coyotes and other animals like raccoons and skunks are also commonly eaten.

A lion and her cub were photo-captured feeding on deer
This lion, F52, has taught her cubs to feed on deer and various wildlife. (UC Davis)

In areas where deer and bighorn sheep or pronghorn antelope overlap in range, some mountain lions will prey on them as well. In the Northeastern California study area, wild horses and pronghorn antelope also are periodically taken.

8. The survival of mountain lions in California calls for more land conservation.

three lions wearing radio collars travel across a field at night
These lions travel by night. All lions need land to roam and live upon. (Irvine Ranch Conservancy)

Only approximately one third of all key mountain lion habitat and corridors in our Southern California study area is currently protected for conservation. Another 20 to 30 percent is partially protected as part of Department of Defense or American Indian Reservation lands.

The research team has collaborated with Dr. Kathy Zeller of the University of Massachusetts to use GPS data, camera data and modeling to identify the most important lands for conservation action so that scarce conservation dollars are spent by governments and others in the most effective way possible for the lions and other wildlife.

9. You can keep yourself and the local mountain lions safer.

A safe hike in the foothills with many small children
The outdoors is safe for humans, pets and lions when precautions are followed. (Karin Higgins/UC Davis)

Safe interactions with our wild neighbors depends on simple safety practices, including avoiding backcountry trails after dark, not hiking or biking alone, protecting your pets and livestock, and learning to see the world through the eyes of wildlife.

Winston Vickers leads research and staff for the Karen C. Drayer Wildlife Health Center’s Southern California Mountain Lion and Bobcat Project.