Photo by D. Sillman
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Last week I talked about the trees in my yard. This week I want to record my observations on the squirrels that live in and feed on those trees! My son-in-law, Lee Drake contends that the single thing that makes an American neighborhood different from neighborhoods in Europe or Asia or Africa is the presence of squirrels. Whether they are running around in the yards, going up and down the trees or darting across the streets, squirrels are quintessentially an American neighborhood fixture! North America has an abundance of squirrels, and they have adapted themselves very well to the presence of humans.
I have written many times about the gray squirrels that gorged at my bird feeders back in Pennsylvania. Their gluttony, their agility and tenacity, and their sometimes silly but occasionally violent interactions with each other, made them great objects for observation and speculation.
On my first night in Greeley back in late July, I was sitting out in my daughter’s back yard. Her two dogs (Gedi and Heidi) alternated between sitting with me and running manically back and forth under the crossing utility lines to bark at two squirrels who seemed to be going across the wires just to get the attention of the dogs. It felt very normal and very home-like to have squirrels close by behaving in such a silly manner.
Photo by D. Sillman
At my new house another set of squirrels were roaming around in the backyard honey locust tree and the front and back yard Ponderosa pines. The seed-rich pods of the honey locust and the large cones of the pines were big attractions for the squirrels! The back yard was covered with chewed-up locust pods, and the soil and gravel under the pines was littered with fragmented pine cone debris. A few days after we moved in Deborah swept the cone fragments off of the back patio, but two days later, the surface was once again
Photo by D. Sillman
cover by debris. Sitting out in our sun porch in the late afternoon or early evening we hear a nearly constant clatter of pine cone fragments raining down on the porch roof.
I watched these new squirrels carefully comparing them to the very familiar gray squirrels that I knew in Pennsylvania. These “Greeley squirrels” were about the same size as my Western PA squirrels, but their tails looked a little bit longer and a little less bushy. Their bodies were also a bit sleeker and trimmer, but that might be due to the many years of nearly constant daytime feeding the Pennsylvania squirrels had had from my black oil sunflower seed feeders! The Greeley squirrels were also less fuzzy looking on the edges of their bodies. The Pennsylvania gray squirrels had white tipped body hairs that set up a hazy aura around them. The body lines of the Greeley squirrels were much crisper and much more clearly defined. The Greeley squirrels were also a different color than the Pennsylvania gray squirrels. They were a uniform, reddish brown all over. They did not have white bellies like the PA squirrels nor did they have the blend of brown, gray, black and white hairs that make up the compromised “gray” of the PA squirrels’ common name.
Realizing this, I suddenly knew that these Greeley squirrels were not gray squirrels (Sciurus carolinensis) at all! They were fox squirrels (Sciurus niger) !
Photo by J. Gallagher, Wikimedia Commons
I have encountered fox squirrels twice before. The first time was down on Assateague Island out in the maritime forest of the National Seashore. Those fox squirrels were the formerly endangered “Delmarva squirrels” (Sciurius niger cinera). The Delmarva fox squirrel look like a gray squirrel (gray-brown body, white belly, big, bushy tail), but they are huge! Gray squirrels typically weigh about a pound, but the Delmarva fox squirrel can weigh up to three pounds! They look like small dogs running around up in the trees! Their larger size makes them slightly less agile and slower afoot than other types of squirrels, and these features increase their susceptibility to both natural and introduced predators and also make them extremely visible to human hunters. This increased predation pressure along with significant habitat loss dangerously impacted the Delmarva fox squirrel populations and caused them to be placed on the Endangered Species List in 1967. Their recovery, however, has been robust, and they were removed from The List in November, 2015.
Photo by D. Sillman
My second encounter with fox squirrels was at my home in Pennsylvania. A large, orange-brown fox squirrel showed up one spring and spent the next year or so hanging out with my local group of gray squirrels. The fox squirrel was significantly larger than the other squirrels in the group (about 1/3 bigger, so nowhere nearly as large as a Delmarva squirrel), and he stood out from the group because of his unusual coloration. He seemed to fit in with the group of squirrels quite well, though. They all ate together at my bird feeders, climbed around in the trees together and did not seem particularly antagonistic or antipathetic to each other. One day, though, the fox squirrel was just gone.
There are ten subspecies of fox squirrels in North America, and the subspecies found in northern Colorado is a relatively recent local arrival called Sciurus niger rufiventu. This subspecies has spread its midwestern range all the way up to the front range of the Rocky Mountains. This subspecies of fox squirrel is about 50% smaller than their eastern counterparts, so looking at these “Greeley squirrels” I was not struck by an obvious size disparity between them and the gray squirrels with which I was familiar.
Why did fox squirrels migrate into the “city forests” of northern Colorado while gray squirrels (with whom they share an extensive midwestern range) did not? A paper describing the ten subspecies of fox squirrels speculated that the tendency of fox squirrels to forage on the ground and to comfortably move between distantly planted trees made them able to move across the even relatively vast, open stretches of prairie. Gray squirrels, on the other hand, strongly prefer habitats dominated by densely planted trees. They also prefer to move up in the trees via interconnected branches (I observed this preference often in my PA gray squirrels!). Gray squirrels would be much less likely, then, to migrate across open grasslands or from distant tree to distant tree than fox squirrels. Gray squirrels are found in a number of cities and towns on the west coast, but that introduction was via direct human intention and action.
Observing the fox squirrels in the honey locust tree: two or three squirrels feed in the crown of the tree at one time. Each squirrel moves about independently of the others, and I have seen no disputes over branch locations or pods selected to feed upon. The clusters of the long, green pods are located toward the ends of the relatively slender, terminal branches, so when one of the squirrels is feeding the branches dip quite low and shake vigorously with any of the squirrel’s movement.
Photo by D. Sillman
The pods are in clusters of 5 to 7, and the feeding squirrels don’t appear to take any time to evaluate or compare the different pods. They simply shinny out to the pod cluster and immediately pull one pod off and begin to feed on its seeds. The squirrel holds the pod in both front paws and maintains his position on the thin branch only by the grip of his rear feet. The squirrel works its way from one end of the pod to the other (like eating an ear of corn!) (the direction of pod consumption is most often from the squirrel’s left to its right).Then the squirrel drops the pod to the ground. Usually the squirrel then moves to another pod cluster often on a different set of branches to continue feeding rather than taking another pod from the previously used cluster.
Photo by D. Sillman
Examining the dropped pods, I note that not all of the seeds in the pod have been eaten, but I cannot tell if this is because the unconsumed seeds were not yet ripe, or if they were smaller than the seeds consumed or had some other feature that caused the squirrel to reject them. My feeling is that the pods and the seeds are so abundant that the squirrels are just being hasty and careless in their feeding. The squirrels can be seen in the honey locust tree feeding on seed pods at almost any hour of the day.
I just noticed that there is a large mass of dried leaves and sticks jammed into one of the high forks of the honey locust tree. The leaf mass looks like the descriptions I have read of a fox squirrel nest. It must be great to live among such an abundance of edibles!
One last point of trivia about the midwestern fox squirrel (Sciurus niger rufiventu)! It was first described and its species name was authored in 1803 by the famous French biologist, E. Geoffroy Saint-Hilaire! Many zoological and botanical specimens from the New World were sent back to Europe for evaluation by experts. Saint-Hilaire is one of my favorites of this time period because of an observation he made about the morphology of a lobster. He noted that the embryology of the lobster (which is in modern terms a “Protostome” animal) developed in a reversed orientation (front to back and top to bottom) than a typical vertebrate (which is in modern terms a “Deuterostome” animal). Saint-Hilaire was ridiculed for these published observations, but he was right! In embryonic development Deuterostomes and Protostomes have reversed head and tail ends, and in Deuterostomes the nerve cord develops on the back (the “dorsal” side) while in Protostomes the nerve cord develops on the belly (the “ventral” side). I find it energizing that my new squirrels were named by such a brave and careful observer!