February 9, 2022
In the oak woodlands of the Willits Mitigation Lands southern piece of property, called Plasma, the deciduous Valley Oaks are full of much life and sounds. Besides the entertaining ‘waka waka waka’ of our resident Acorn Woodpeckers, the churring of our new winter migrants, the Lewis’s Woodpeckers, is still a delight to hear. Another sound I am hearing everywhere in this woodland is the loud barking and chirping sounds from the Gray Squirrels who are running and jumping from oak tree to oak tree.
The Western Gray Squirrel, Sciurus griseus, is one of my favorite rodents to watch. It also happens to be diurnal, which means the Gray Squirrel can be observed during the day. In the fall they are preoccupied with the task of gathering acorns and other winter foods, but what are they doing now, in the winter? They are not sitting around doing nothing that is for sure. As I walk through this forest I hear and see them running up and down the trees, chasing each other in what looks like circles. The pair do not seem to notice me at all as they run on the ground, jumping up a trunk, winding around the trees as they move higher up, then doing an impossible aerial jump to another tree. They appear to be flying above my head. Mating and bonding behavior begins in December and can go through June and includes biting and wrestling. It looks like good energetic fun yet upon watching the videos it is clear there is more to it than that!
There is another type of tree squirrel that can be confused with the Western Gray Squirrel and that is the Eastern Gray Squirrel, Sciurus carolinensis. This squirrel was introduced to the west coast in the early 1900’s along with the Eastern Fox Squirrel, Scirus niger. Both are squirrels that live well with humans in urban and more developed areas. Since their introduction their populations have increased in areas of southern California, Sacramento, and Sonoma County. So far, I have not seen either of these non-native species in our county, but they have been reported on the coast and in Lake County. The biggest difference between the Eastern Gray Squirrel and the Western is that the Eastern is smaller and browner overall, with brown on its face and in its tail which replaces the gray, white, and black as seen in the larger Western Gray Squirrel. The Eastern Fox Squirrel is all brownish red with pointier ears. Both introduced species prefer to live in city parks and not in rural woodlands, and that is a good thing for the Western Gray Squirrel because they are direct competitors for the same food and shelter resources. Washington State listed the Western Gray Squirrel as threatened in 1993 due to the steep decline in population numbers due to the introduction of the two eastern species. They are now found only in a small part of their former range in California mainly because they are dependent on large stands of trees, preferably oaks, to serve as their homes and food sources. Much of these forest-types have been removed.
According to C.A. Clark in his article for Bay Nature published on May 28th, 2019:
“Western grays are true woodland creatures and need a continuous stretch of mature oak trees to provide their food and shelter. They are highly arboreal, preferring to be up a tree or near a tree, and will not use fragmented habitat with lots of exposed spaces and few trees. The bulk of their diet is acorns, pine nuts, and truffle-like underground fungi, all of which come from trees. Acorns and pinecones are produced by mature trees, and the truffle-y fungi are species that live in symbiotic relationships with the roots of trees, helping them to take up nutrients and resist disease (western grays themselves are a big positive for forest health since they spread the spores of the truffles around when they eat them). While more aggressive with other squirrel species, they are much more timid with humans, preferring to make their nests away from busy human-created areas. They have only one litter a year.”
These are all reasons why the Western Gray Squirrel populations in urban areas have declined while the other two non-native species have increased. Eastern Gray and Fox Squirrels are more ecosystem flexible like the Norway Rat, and do not mind close contact with humans. Willits is still a rural area with plenty of tree cover, and though wildfires, cars, and tree cutting has a negative impact on these important oak woodland species, we fortunately have an abundance of Western Gray Squirrels.