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Lion's bane

Lion's bane Emi
03 Aug
2015
Despite protection from hunting, the annual survival rate for mountain lions in South California is dangerously low. A 13-year study details how they are mainly killed by their greatest threat, human activity

With the widest range of any wild animal in the western hemisphere, pumas roam the rough margin of mountainous regions from the Andes up to the peaks of the Canadian Yukon. For centuries, mountain lions (aka pumas, cougars, catamounts or panthers) have been imbibed into human culture and are, these days, the mascots for dozens of sports teams. 

For the lions, however, this interaction is not so light-hearted. The development of towns and roadways to support a burgeoning population of 20 million means human and mountain lion habitats are closer than before. In a 13-year study, the University of California, Davis has been looking at the impacts of this proximity. Focusing on an area in the South California region, it found that over half of all mountain lion deaths were caused by human activity.

The two habitats of the eastern peninsular ridge and the Santa Monica mountains are separated by a busy interstate and a network of roads and towns. While it is illegal to hunt mountain lions in California, 17 per cent of the animals were shot for ‘depredation’ because they had become a threat to people and domestic animals in nearby towns. Other causes of death were by illegal poaching and man-caused forest fires. 

pumas2Map showing the two groups of GPS co-ordinates for mountain lions in the Santa Ana and Southern Peninsular mountains (Image: University of California, Davis)

ROADKILL

The biggest killers, however, are motorists. Interstate 15, a ten-lane highway separating the two mountain ranges, has become nearly impossible for the lions to cross. It is estimated the surrounding (and expanding) network of roads can hold 250,000 vehicles a day. For this reason, 28 per cent of mountain lion deaths in the sample population were from vehicle collisions.

However, the interstate poses another, less immediate threat. By cutting off the Santa Ana mountains from the rest of the peninsula, the gene pool has become restricted and is beginning to decline. Without more biodiversity, the lions can and will become more susceptible to disease.

Winston Vickers, lead author of the study, said ‘nowhere in the US, outside of the endangered Florida panther, have mountain lion populations been documented that are this cut off and with survival rates this low. The odds of an individual animal making it across I-15, surviving to set up a territory, successfully breeding, and then their offspring breeding so the genes are spread throughout the population is harder to have happen naturally than one would expect.’ If adult mountain lions don't make it from east to west over the interstate, the Santa Ana lions are expected to deteriorate. 

coygarMountain lion warning on a road in Arizona (Image: Shutterstock)

SHRINKING GENE POOL

During the 13 years of the study, only one mountain lion is thought to have made it westwards across the interstate. M56, a male adult, made it from one side to the other and successfully produced at least four offspring before a car ran him over. Of the four, one was taken into captivity for being too familiar to people, another was also hit by a car and the third was poisoned. The fourth, a female, raised two kittens to adulthood, one of which F126, is known to be alive.

‘So all the genetic hopes of this population may be pinned on this one animal, F126 – a female we know is circulating,’ said Vickers. ‘Given the odds of that female producing kittens, and those kittens producing kittens, it will take generations and generations to see if M86’s effort in crossing the road was worth it.’

While fragmentation cannot be reversed, further development-based fragmentation can be reduced through proper land use planning. Meanwhile, ways to reduce roadkill such as exclusion fencing are in the in discussion and planning stages. ‘Where safe crossings are not currently present,’ says Vickers, ‘we are very involved in promoting planning and funding for those. However, the process can be years long and expensive – in some cases tens of millions of dollars.’

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