Bobcats _2015_04_23
The kittens before they were ear-tagged. Biologists removed them from the den to do the ear-tagging, and to take blood and tissue samples, before returning them to the den. Image: Santa Monica Mountains National Recreation Area 

Earlier this week, biologists working in the Santa Monica Mountains National Recreation Area in Los Angeles got to play with a pair of absolutely adorable blue-eyed bobcat babies. Well, they weren't playing with them exactly; they were affixing them with small ear tags so that researchers will be able to continue to identify them as they grow up.

It's all part of a study that's been on-going for nearly 20 years, which looks at the ways in which carnivores like bobcats (Lynx rufus) are affected by urban development. Los Angeles, after all, is one of the most heavily urbanised cities on the planet.

Earlier this year in the journal Ecological Applications, University of California, Los Angeles (UCLA) researcher Laurel Serieys, together with colleagues from UCLA, Duke University and the US National Park Service, reported that LA's bobcats were being stymied by the city's notorious traffic.

The researchers collected blood and tissue samples from 365 bobcats and compared their genes to work out a sort of bobcat family tree. They found that the area's 405 and 101 freeways, among the most congested freeways in the country, act as barriers to gene flow, resulting in three distinct, genetically isolated groups of cats.

The widest-ranging population is found in the Santa Monica Mountains (the orange dots). The second population lives directly north of the Santa Monicas, opposite the 101 freeway in the Simi Hills (the yellow dots). The third group (green dots) lives in the highly urbanised areas of the Hollywood Hills and in Griffith Park, where they share their space with the famous mountain lion P-22.

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Because the three groups are isolated and are prevented from mixing their genes, the cats are already becoming somewhat inbred – especially those east of the 405.

Unfortunately, the pointy-eared cats have to contend with more than just busy freeways. The population north of the 101 suffered an outbreak of mange between 2002 and 2006, which was associated with the use of rat poisons. When it comes to bobcat genetic diversity, the impacts of disease on that population were even more severe than the effects of freeways.

There is a silver lining however: even in the face of genetic isolation, natural selection appears to be working to preserve variation in genes that are fundamental to maintaining the health of individuals. "These findings suggest that all is not lost in bottlenecked populations because natural selection can still act," said Robert Wayne, a professor of evolutionary biology at UCLA and senior author on the paper, in an official statement.

But cats facing the combined effects of isolation and rat poison will have a difficult time surviving in the long term. So what can be done to help these urban carnivores thrive even in the face of development? For a start, we can ban the types of rat poisons that lead to mange. We can also construct wildlife crossings to allow animals to move over or under busy highways. At least one such crossing is currently being planned. Once completed sometime around 2018, the two populations on either side of the 101 freeway may have a chance to mingle.

In the meantime, researchers continue to monitor LA's bobcats. The two kittens, just three or four weeks old, are being called B326 and B327. Their mom, B255, has been under the watchful eye of researchers since 2010. Her kittens were tagged while she was away from her den, probably hunting for food.

Bobcat With Eartag _2015_04_29
B327 with her ear tags in place. Kittens this young are never fitted with GPS collars, so the ear tags help identify the cats when remote cameras snap images of them. The youngsters can also be tracked thanks to mom's GPS collar. Image: Santa Monica Mountains National Recreation Area/Facebook