Bolsa Chica Ground Squirrels

by Mike Armstrong

PROBABLY the most visible native mammal on the Bolsa Chica Ecological Reserve is Otospermophilus beecheyi, the Beechey’s Ground Squirrel.   They are seen in many parts of the reserve, but most obviously along both sides of the Mesa Trail and on the slope above the trail along the Pocket Wetland.  This species lives in CA, OR and Baja California, and is now expanding its range into SW Washington and SW Nevada.  A pair of ground squirrels in our climate will normally have up to nine pups, fewer in colder areas.  These large litters allow for a high rate of predation, which, as we will see, is good for Bolsa Chica’s raptors and other squirrel-loving carnivores, but keeps the squirrel population viable too.
Ground squirrels may live up to six years here.  The female does most of the direct care of the pups, but the male has vital roles as a sentry and in defending against snake attacks on their burrows.

As their scientific name shows (‘spermatos’ means seed and ‘phileo’ means love in Greek), the ground squirrel is a seed lover, but also eats many green plant materials and some insects, especially during drought conditions.  They don’t need liquid water to survive, since their digestive systems can convert carbohydrates from seeds into water.

They live in burrows at night and in inclement weather.  The burrows are about 4-5 inches in diameter with larger main entrances, can be from five to thirty feet in length, and go as deep as six feet under the surface.  Several families may make large colony burrows over time, but each family keeps an individual entrance.

Deep burrows among rocks are favored when available since they can prevent predators like coyotes and badgers from digging out the occupants.  Rocky areas, such as the bluff above the Pocket Wetland, are few at Bolsa Chica, but we have no badgers.  (Although the “tejon” (badger) is returning to Orange County.)

As with many herbivores, most predation falls on the young pups.  Rattlesnakes, a major predator, have trouble swallowing adult ground squirrels but can and do eat many pups.  Birds like Great Blue Herons and Great Egrets eat many, as do the large raptors like Red-tailed Hawks.  Herons and egrets sometimes eat adult squirrels but use special techniques for killing them and making them small enough to swallow.  Some parent birds apparently teach these to their young, some don’t.

Ground squirrels protect themselves against most predators mainly by vigilance and communication of threats to the community.  When you see squirrels foraging on the ground, there is usually one, typically an older male, sitting on top of the fence or a tall plant.  He is a sentry.  Should a hawk, heron, coyote, or other predator be sighted, the sentry will utter a high-pitched alarm squeak that to me sounds like “KEEK-cha-cha!”  It means “get in a hole!” Usually, the rest of the squirrels respond very quickly.  Should the intruder be a snake, the response from the other squirrels nearer to the threat will be a series of lower-pitched notes that are repeated until help arrives or the threat moves on.

RATTLESNAKES are one of the primary predators of juvenile squirrels.  Pups are often caught in their burrows, trapped underground.  Rattlers are called pit vipers because of a pair of small organs below their eyes that detect the ultraviolet radiation of the body heat of mammalian prey—they can “see” their prey in the absolute dark of a deep squirrel burrow.  The protective mission of adult squirrels is to “keep that damn’ serpent outa the house!”   They do this in a variety of ways.

Say a full-grown forty-inch Southern Pacific Rattlesnake is cruising the mesa, looking for dinner.  It smells or hears ground squirrel pups in a nearby burrow and glides silently toward it.  What’s to stop him from entering and eating them?

Well, ground squirrels and rattlers have been living here for countless years, and the Beechey’s have developed a menu of passive and active defenses against the rattlesnakes.

In the area of “chemical warfare,” female squirrels often seek and find newly-shed rattler skins.  First, they roll all over them, transferring snake smell to their own coats.  Then they eat the skin and nurse their young.  The point of this strange behavior is to imbue the prey with the smell of the predator.  Rattlers have a very sensitive sense of smell, and, after this procedure, a rattler is more likely to pass by the burrow of the anointed squirrels, smelling a competitor and thinking that the inhabitants of this burrow are likely already eaten!

In the same area of “chemical warfare,” many populations of adult Beechey’s have developed a total or partial immunity to rattlesnake venom.  Even partial immunity saves lives of adults because the snakes often don’t fully envenomate prey that they can’t eat.  They try to save their limited supply of venom for dinners they can enjoy or predators they can’t evade.  This immunity also allows the adult squirrels to be more aggressive in fighting rattlers in defense of their pups than they might otherwise be.  They know instinctively that even a successful strike doesn’t necessarily mean death or serious injury.

Beechey’s also use the rattler’s UV sensors against them.  The squirrels accomplish this by sending extra blood to the blood vessels in their tails, which causes them to heat up abnormally.  This spoofs the snake by showing a second squirrel UV image, which the squirrel enhances by stiffening and raising his tail and waving it.  This gives the snake TWO moving UV targets and may convince it to give up the hunt either through confusion or just not wanting to tackle two opponents.  In some cases, an entire colony of squirrels will start this behavior, giving the snake the impression of an angry crowd!

When these defensive measures don’t deter a snake from approaching a burrow, adult squirrels may physically attack it, using tactics very much like the ones snake-eaters like the Asian and African Mongooses use to wear down their prey—provoking strikes, dodging them, then biting the snake before it can recover.  This is intended to wear out and discourage the snake, not kill it, since ground squirrels aren’t snake eaters.  Videos show that squirrels can wear out a snake, even larger, faster striking snakes than rattlers, by their daring acrobatics. Snakes may be accomplished assassins, but ground squirrels can be little ninjas when they are defending their young!

Unfortunately for the squirrels, but fortunately for the rest of the environment, not all squirrels are so diligent in defending their young, and the young, being young, don’t always practice good defense.  Sometimes they stay out too late after a sentry alarm and get caught too far from a burrow to avoid a hawk or a coyote.  Sometimes they get so caught up in eating luscious Yellow Bladder Pod or in a game of tag that they don’t hear, or don’t heed, Pop’s warning squeak at all.

A ground squirrel’s life isn’t all life-or-death confrontations with predators.  When they are alone with a trail camera they show lots of signs of play, including mock combats, races and chases, and acrobatics on limbs, fences, and on our Native Plant Growing Space equipment!

The right ratio of squirrels to land is good for the environment. It keeps the carnivores fed and provides housing for many other species in both occupied and abandoned burrows.  The burrows also allow rain to percolate deeper into the soil than it would without them.  But what is that right ratio?  What if there are too many squirrels?

THE answer to that usually depends on who is making that judgement and why.  My own experience of this comes from my youth on a ranch in central Sonoma County when it wasn’t yet the Wine Country. Aromatherapy for us was the smell of livestock, the smell of money.  The more stock you could run on a given piece of land, the less poor you thought you would be.

In 1948, the various governments were in full support of attitudes toward nature that were relics of the frontier.  If something didn’t obviously help you make a living, it was an enemy.  For example, the State Fish and Game (NOT “Wildlife” then) Regulations carried a long list of animals considered predatory.  “Varmints” we called them—animals and birds considered damaging to agriculture and/or game populations.  They included all carnivores—birds, mammals, snakes, and many of what we would now consider songbirds: jays, magpies, finches, flickers and other woodpeckers.  Some of these species were already extinct or nearly so in many areas of California.  Some herbivores were also on that list, ground squirrels among them.  All of them were considered unprotected, meaning they could be killed without a license or any other control.  Game animals and birds were subject to controlled harvesting as they are now.

But the various federal, state, and local governments went a step further with some species that were considered especially dangerous to agriculture, especially carnivores that were considered dangerous to livestock.  At the behest of lobbyists for the cattle and wool-growing associations, cash bounties were offered for the killing of predators, especially coyotes, bobcats, and mountain lions. The other two apex predators, grizzly bears and wolves, didn’t survive the end of the frontier period for similar reasons.

Add the disastrous effects of DDT on carnivorous birds like hawks, owls, and vultures, and the ground squirrel was left with very few predators.  Their populations soared.  With the overgrazing that was regularly practiced to squeeze the last pound of beef, the drop of milk, and the last ounce of wool out of the land, our (then) copious winter rains ran down the ground squirrel burrows and loosened land denuded of native plants by grazing, and erosion began—huge gullies and whole hillsides slipping away. SOMETHING NEEDED TO BE DONE!

The local solution to too many ground squirrels in our area, aside from shooting, trapping, and cussing, was to poison them with strychnine baits.  This did kill a lot of squirrels, but not all of them.  It also killed everything that liked to eat dead ground squirrels, meaning all remaining carnivores and scavengers, not to mention quite a few valued dogs and cats.  I lived there twelve years and often returned in the following years to visit and help out.  In all that time I never saw or heard a coyote, a fox, or a bobcat.  Even vultures and ravens were scarce.

The squirrels, without predators, came back in droves and only declined to a sustainable (for both squirrels and ranchers) level when the government dropped the wool subsidy and sheep overgrazing declined.  Banning the use of DDT brought back many of the avian raptors, and the squirrel population stabilized so that they were present, but not a cause of erosion and landslides.  When I returned to the ranch (now part of a Land Trust) after many years of absence, one of the first things I saw was pair of coyotes!  And then heard Papa Beechey’s alarm squeak from atop one of the remaining Mexican-era stone field walls!


A NOTE OF CAUTION: ground squirrels are handsome, cute, and easy to observe.  But handling them is dangerous.  They should not be allowed to climb on people or live next to people.  Taming them so that they will eat out of your hands is easy and potentially deadly for both you and the animal.  Ground squirrels in the Southwest US carry a long list of diseases that people can get, and every year some do, almost always from handling the animal so that they are bitten by it or by the fleas that almost all wild animals carry.  Feeding them in your neighborhood may encourage them to move into yards and burrow near people, potentially infecting pets.  Feeding them in the wild may increase their population beyond the holding capacity of the natural food in the area, leading them to depend on humans for food and become aggressive little panhandlers, leading to bites, including flea bites.  When they spend time looking to people in the wild for food, they aren’t eating the native plants that really nourish them, and the young squirrels may not even learn what to eat and how to eat it.  And they certainly aren’t paying proper attention to predators when they are looking for a handout from us.  It is best to leave them be.

Photos from the Growing Space Wildlife Cams

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