Durwood Allen has always been a name on my mental list. As wildlife biology major in college I always managed to drift towards one or two of his research papers as a source of primary material. Although the wildlife biologist eventually went on to national status, he spent a good deal of field time working for the old Michigan Department of Conservation from 1935-1946. Perhaps because he earned his PhD from Michigan State University, I naturally thought he was one of the best (which he was, of course, but not for the limited reason I just mentioned). Among his many publications, perhaps the Wolves of Minong, about Timber wolves, was his best known but the one that brings me to this blog posting was Michigan Fox Squirrel Management (1943). I know you all have this on your summer reading list but few are wiling to admit it.
Every time I try to look up something about Fox Squirrels I end up with citations referring back to this work. Because the research was done primarily in Michigan it is a great source for finding out why and how Michigan Fox squirrels do what they do. True, these squirrels pretty much do the same thing wherever they live, but they do look -and occasionally act -different when “out-state.” Their scientific name Sciurus niger, for instance, rather than meaning “foolish brown road crosser” actually means “black tail user” (loose translation, mind you). Midwestern Fox Squirrels are orangish brown and they only rarely come in black. Out east, however, they often are black, or have black heads with white muzzles and all sorts of unnatural coloration. They were originally named based on an “out east” specimen (by Linnaeus in 1758) and thus the reason for the black coloration reference.
While recently watching a Fox Squirrel dedicate a day’s work towards winter nest-building, my curiosity was piqued. This fellow was doggedly (squirredly?) gathering up leaves and carrying them high aloft to his nest structure. He was one of our so-called marsh squirrels which subsist on the fringe of Cottonwood Trees surrounding the cattail marshes. His route from ground to nest and back was a very specific one. At the base of one Cottonwood tree he would quickly gather a mouthful of leaves and scurry up the trunk on the eastern side. At a certain point he would curl around to a branch on the southern side of the trunk and perform a pair of flying leaps taking him to his nest via three separate branches. The leaps are admirable, especially given the fact that Fox Squirrels are not considered to be as agile or able as their lesser cousins the Grays (watch the movie clip here). He followed this circuitous path without variation for as long as I watched him. I can’t tell you how many times, but it was longer than a normal attention span would allow.
My Durwood Allen moment came when trying to discern the finer points of nest building behavior. Rather than make something up (an entertaining, albeit shameful option) I chose to augment my observations with real research results. My observations were clear enough. This squirrel wasted no time at his nest. He rammed the new load of leaves into a side entrance, shuffled them around a bit, and quickly emerged for another foraging trip. The ball shaped structure consisted of a combination of sticks and leaves and was located right up against the trunk of the tree. According to Allen’s work, the typical Fox Squirrel nest has a side entrance, is about 7 inches in diameter, and located 30 feet up. It looks like my squirrel read the rulebook.
Fox Squirrels – at least those individuals who survive centerlines and curbs – tend to built two nests per year. They construct loose summer nests in the outer branches and typically resort to tree cavities in the winter. Where tree cavities are at a premium in the cottonwood tree lines, our winter squirrels construct tight winter nests right up next to the trunk.
There is no correlation between the size or location of squirrel nests and the severity of upcoming winter weather. I guess you could say that crumbling winter nests are an indication that a hard winter is in progress because these structures quickly fall apart if not constantly maintained. Since dead frozen squirrels can’t maintain their nests properly, their bad nests are some measure of bad winters (not a forecast, but more like an Indian weather rock prediction). Looking at the size of the squirrels, as opposed to the size of their nests, is probably a better way to judge their individual survival chances. It goes without saying that you must remove the road factor from this equation.
Watching my average-looking squirrel leaping through mid-air caused me to wonder how much the average Fox Squirrel weighs. Allen reveals that the average adult weight of his Fox Squirrel population was 28 oz. – or a little over a pound and a half. Any individual around this target weight should have no problem making through the winter. The heaviest one that Allen recorded weighted in at 43.5 ounces – over two and a half pounds. I doubt that portly rodent would have been able to make the nimble jumps necessary for cottonwood climbing. Such a beast would fit in nicely with the current crop of piggish Fox Squirrels that park themselves at our backyard bird feeders far from the marshes.