As SoCal Squirrels Vie For Territory, Smartphones Can Keep Score

Here's another story in our series on citizen science in California, our way of celebrating Citizen Science Day on April 16.

As a young child, I spent many nights sleeping at my grandparents' house in the flats of Northridge, not far from the CSUN campus. Upon waking I'd tiptoe down the hallway, carefully so as not to let the floorboards creak under my weight, and climb onto their bed, a perch from which I could survey the early morning goings-on in the backyard. Thanks to all the fruit trees my grandfather had planted over the years, it was a haven for local wildlife.

I watched crows hop across the grass, hummingbirds zip among the flowers, and squirrels chase each other along the fences and power lines. If you grew up, as I did, in the San Fernando Valley, you could be forgiven for thinking of the valley's resident squirrels as locals.

It was not until many years later that I'd come to learn the truth: those cute, wide-eyed squirrels that I'd spent so many hours watching from my grandparents' bedroom? They were trespassers from a distant land, invaders who had driven out the locals nearly a century before — and now the subject of a citizen science project to track their presence.

The squirrels' conquest began several miles to the south, through the Sepulveda Pass. In 1904, the Veteran's Administration hospital in West LA was called the "Sawtelle Veteran's Home," and it served vets from both the Civil and Spanish-American Wars. The Civil War vets were often from the American South, places like Kentucky or Tennessee. Some of those vets brought their pet squirrels along with them. (Like our modern backyard chickens, these animals were pets right up until they wound up in a stewpot.)

Here is where verifiable fact gives way to folklore: it is said the vets would feed their furry friends with table scraps. Administrators at the V.A. found this an unsuitable use of government-funded resources. Faced with the prospect of letting their companions starve, the vets took a slightly more welfare-oriented approach. "They turned the squirrels loose, right there on the V.A. grounds," Jim Dines, curator of mammals at the Natural History Museum, said several years ago when first recounting the tale for me.

For a time, the squirrels remained in the vicinity of the V.A., but thanks to the ever-increasing erection of telephone wires and above-ground cable, the squirrels learned they could use them to avoid getting hit by cars or nabbed by domestic cats. County records reveal that by the 1930s, the invaders – eastern fox squirrels, Sciurus niger – had discovered an agricultural bounty waiting for them in the valley, to the detriment of local farmers. Los Angeles at the time was far less developed than it is now, much of the valley having been occupied by orchards of citrus and walnut.

That's probably not the only time that eastern fox squirrels were introduced to the Southland, but as a result of their can-do spirit and general adaptability, they rapidly came to dominate the region.

Our native western grey squirrel, Sciurus griseus, is something of an ecological diva. Whereas the eastern fox squirrel is content to feast on anything and everything (a camera trap deployed by Natural History Museum researchers once caught a squirrel chowing down on a pizza crust), its western grey relative is far pickier. It requires native oak trees to survive, depending on its acorns and on the fungi that grow among its roots for sustenance, along with the leaves and fruits of a few other native trees that commonly grow alongside oaks.

While our urban development pushed these habitat specialists into the few remaining native oak forests in the San Gabriel, Santa Monica, Santa Susana, and Verdugo Mountains, there they remain at risk of displacement by their eastern counterparts. Because while the fox squirrels are happy living in the suburbs, they're equally happy establishing a homestead in undeveloped areas.

Some years ago, before Julie King became the Catalina Island Conservancy's Director of Conservation & Wildlife Management, she studied squirrels. In particular, she was interested in understanding the squirrels' inter-species dynamics in places where their ranges overlapped: did they get along, did they fight? And if so – who won?

She was surprised to find that in antagonistic interactions, it was usually the grey squirrels that started the fights, and it was usually the greys that triumphed. Instead, the fox squirrels' overall domination might have to do with their fecundity. They deliver litters twice each year, while grey squirrels reproduce just once each year. The natives are simply outnumbered by their competition. In spots with sufficient resources for both species to coexist, they seem to get along just fine, but in smaller habitats, the fox squirrels quickly prevail. In one spot in Pomona several years ago, the wholesale replacement of grey squirrels by fox squirrels took just three years.

A 2013 survey conducted on behalf of the LA Zoo found that western greys persist west of the 405 and east of the Cahuenga Pass, plus one possibly genetically isolated population within Griffith Park. "In between the 405 and the 101, [in] Beverly Hills, Bel Air, Franklin Canyon, Stone Canyon…they're just gone," said mammal researcher Miguel Ordeñana, who is also citizen science coordinator at the Natural History Museum. "I have a specimen that I use for outreach a lot that's from Beverly Hills, a specimen collected in the 1970s. But they're not there anymore." In less than fifty years, the species simply disappeared from the neighborhood.

Researchers at the Natural History Museum, like Dines and Ordeñana, need help ascertaining the future of western grey squirrels. As with the RASCals project, interested folks can snap any photo of a squirrel with their smartphones and send them to the Southern California Squirrel Survey through the iNaturalist app, or by emailing the photo to nature@nhm.org or uploading the photo to Facebook, Instagram, or Twitter using the hashtag #NatureinLA. (Southern California is also home to the California ground squirrel, Merriam's chipmunk, another invader called the eastern grey squirrel, and a handful of desert species.)

Thanks to simple photos matched with timestamps and geotagging data, researchers can document the expansion of eastern fox squirrels and the simultaneous disappearance of western grey squirrels in an effort to understand what factors allow the two species to coexist peacefully and where the best spots are to focus efforts to protect western greys.

While the species as a whole appears to be doing just fine, with a range extending from central Washington to Baja California, our local populations are clearly at risk, both from increasing urban development and from displacement thanks to eastern fox squirrels. And western grey squirrels play an important role in native oak woodlands. By burying acorns and forgetting to dig some of them up later, they help oaks to reproduce. They also turn over the top layer of soil at the base of oak trees by digging, which aids the trees in retaining water during the driest parts of the year. The oaks, in turn, provide food and shelter for a wide variety of birds, mammals, insects, and other critters.

And then there's the other problem: while residents of the San Fernando Valley are clearly accustomed to the appearance of eastern fox squirrels, in other places where homeowners can remember a time before they were ubiquitous, they're often thought of as unwelcome pests. What should be done in those cases? Elsewhere, people deal with invasive species – like crayfish and lionfish – by putting them on the dinner plate. Should we perhaps once again be pondering the palatability of squirrel stew?