A small population of cougars lives at the margin of metropolitan Los Angeles in the Santa Monica Mountains. But the isolation of the group, surrounded by freeways and development, has threatened their genetic diversity according to research published this week in the journal Current Biology.

Lead author and National Park Service biologist, Seth Riley, said over the 12 years of the study only one individual has crossed a freeway from outside the region to join the group and inject diversity into the gene pool.

Similarly only one male member has left the group, P-22, who made his way out of the Santa Monica Mountains and into Griffith Park. However, his new habitat is an even smaller and more isolated one with no opportunity for mating.

Under normal circumstances almost all of the young members of a population would leave their home range to seek mating opportunities elsewhere. But the danger of crossing major freeways has made that almost impossible for the cougars in the Santa Monica Mountains.

The isolation of the Santa Monica Mountain group has amplified the effect of behaviors that are rare in other more diverse groups of animals like inbreeding, and intraspecial killing of siblings, mates or young.

Riley and his team propose building wildlife "overpasses" that could connect natural habitats across freeways and provide a throughway for cougars to leave and enter the Santa Monica Mountains.