Of all the East Coast/West Coast battles that have played out over the last century, perhaps one of the least talked about and most adorable is the one happening right now in Los Angeles and its environs among squirrels. One type of squirrel, a native species to California and coastal Western states, has been steadily losing ground to its East Coast counterpart, a transplant that hitched a ride to the area more than 100 years ago and has since become "the most common squirrel in much of Los Angeles," says LA Observed. SoCal Wild, a wildlife blog, has the story of how the recent arrival, the Eastern fox squirrel, muscled in on the local Western gray squirrel's turf and what the repercussions have been.

As its name might suggest, the Western gray squirrel is a staunch West Coaster. Native to the coastal states (California, Oregon, Washington), they're silvery gray with white stomach fur and they like to eat tree nuts. Their dietary preference is important: when they hide nuts and forget about them (adorable!) or when they leave their droppings throughout the woods (less adorable), they help propagate trees. Their useful scat can also help distribute a fungus that helps the roots of oaks and pines better absorb water.

They are totally unlike those trash-eating Eastern fox squirrels. A "fast procreator with an appetite for everything," these trumped-up rats first arrived at the turn of the Twentieth Century with the arrivals at what would eventually become the Veteran's Affairs compound in West LA. The squirrels were considered "pets," but it wasn't long before these reddish-brown beasts were escaping, eating nuts and fruit right off the trees, and making nuisances of themselves.

When they aren't eating and mating, Eastern fox squirrels are also pushing the limits of their range, always expanding into new territory. They had a little help from humans along the way. A graduate student's 2004 study found that people were trapping Eastern squirrels and unloading them in different locations—areas where Eastern squirrels hadn't been before. "Easties followed human development and slowly made their way along SoCal lowlands, setting up shop while grays in their pathway, quietly retreated into pocket populations."

The retreat of the Western gray squirrel population into isolated groups means that, like LA's local mountain lions, the Western gray population in inbred. They're held in their enclaves by traffic and civilization and unable to adequately branch out. There's a lot working against them—genetic isolation, increased competition from those stupid East Coast squirrels—on top of universal squirrel problems like having to avoid accidentally eating poison or becoming roadkill, or loss of their habitat. The result hasn't been positive for the Western gray squirrel: "Even with a few studies on the grays, it's apparent their numbers are decreasing."

A disappearing squirrel population may not immediately seem like a grave problem, acknowledges Alan Muchlinski, a CalState LA professor who's spent years studying the Western gray. But it's a fact that "introduced species cause problems with the natives and affect the ecosystem," and he cautions that "We just don't know what the complete consequences are" to this East Coast squirrel takeover.

Studies have shown that these two very different squirrels can coexist. Chris DeMarco, a graduate student "immersed in the squirrel world for three years" and working under that long-time CalState squirrel researcher, has found that Ferndell in Griffith Park seems to have both Western grays and Eastern fox squirrels and they seem to be able to share the same space. But that might not make any difference in the long run if Eastern squirrels expand their range to include local forests, like the ones near Mt. Wilson. "[T]hat could be catastrophic for SoCal grays," says DeMarco.

· Battle of the LA squirrels rages on [LAO]

· A Tale of Two Squirrels [SoCal Wild]

· Meet the Murderous, Inbred Mountain Lion Family of the Santa Monica Mountains [Curbed LA]