By Jerry Sullivan
I didn't plan to make a career out of writing about squirrels. I wrote a column a year ago about black squirrels--a color phase of the familiar gray squirrel--and about fox squirrels, a related but quite separate species. I noted that although the standard reference--Hoffmeister's Mammals of Illinois--declared that black squirrels occur along the North Shore, I had seen one on Stratford Place, which at 3400 north is decidedly not North Shore.
Fox squirrels, I wrote at the time, occurred in two places in Chicago that I knew of. One population lived in Lincoln Park in and around the bird sanctuary behind the totem pole at Addison. The other lived along the river in Horner Park between Irving Park and Montrose. I asked people to write if they knew of fox squirrels in other areas or if they had black squirrel sightings to add to mine.
I got more mail from that one column than I usually get in a year. People reported sightings of black squirrels up and down the lakefront and on the northwest side. Carolyn Pulizzi wrote of a population of fox squirrels in her backyard in the neighborhood around Diversey and Pulaski. So I wrote another column reporting on what my readers had found, and that column produced another pile of mail. There are a lot of people out there paying attention to squirrels. Rick Pope sent me pictures of black squirrels sitting on the back fence of his house on West Barry. Fred Church added some historical perspective with a report that he had been seeing black squirrels on Stratford Place for 28 years.
From the northwest side, Cathy Bloome told of black squirrel sightings on Sunnyside between the 5700 and 5900 blocks. Roland Flessner, who commutes by bike from near Irving Park-Cicero-Milwaukee to Cicero and Touhy told of sightings near his home in Lincolnwood and along the North Branch trail. Ed Cohen sent me a shaky Polaroid taken in his backyard on Chase of a nearly black squirrel. He had earlier reported seeing a pure black squirrel in the same location. His latest letter pointed out that the photographed squirrel had some gray in the tail. "The one I wrote about at first," he writes, "was pure black. I talked to a woman on the street who is a real estate agent, and she told me that someone moved in from Ontario. I guess that my original sighting hitched a ride." To cap all this, I saw a black squirrel hanging around the alley where I park my car--less than a block from my own apartment.
Also, Pulizzi sent me photographs of the fox squirrels in her backyard. I wasn't entirely sure that the pictures showed fox squirrels. The coloring was right--a buffy orange hue on the underparts and ears--but the animals didn't look quite large enough. Fox squirrels are noticeably bigger than gray squirrels.
It seemed obvious that I would have to write another column in response to all this mail, but I didn't have a peg to hang one on until I saw a story in the Tribune about some people who loved squirrels so much they had formed a club to bring together like-minded Sciurophiles to pool their admiration for these adaptable arboreal rodents. The story quoted Joel Brown, an associate professor of biology at the University of Illinois at Chicago, who was identified as someone who had been studying squirrels for 13 years.
So I looked up Brown and asked him about our local squirrels. First I showed him Pulizzi's pictures of her backyard squirrels. He instantly verified that they were indeed fox squirrels. He also told me that there were fox squirrels in Grant Park and in a number of suburbs as well.
In the days before the steel plow and the two-man saw arrived in Illinois, gray squirrels lived in the dense woods that grew in the river bottoms and other places protected from fire. Fox squirrels occupied the oaks of the savannas and the woodland edges. Settlement shattered all the old categories, ending the tidy ecological separation between the two species and throwing them into direct competition. From 1900 to 1950 the fox squirrels seemed to have the edge in this contest. Their numbers increased locally, regionally, and statewide.
Since 1950 the balance has shifted. Gray squirrels are advancing at every level--statewide, regionally, and locally. Brown is watching the process around his home in Oak Park. It's a slow shift, block by block. "We had nothing but fox squirrels when I moved there, but the grays are slowly advancing." It might take eight years to expand their range by one block.
Why is this happening? Brown has a hypothesis--and he emphasizes that it is no more than that--based on the original habitat preferences of the two species. The forest interiors where the gray squirrels lived are places squirrel food is rather hard to come by. The seeds of maple trees are rather small. The tall shrubs are generally not nut producers, and the herbs of the ground layer are mostly spring ephemerals that sprout before the maples leaf out in spring and wither away before mid-summer. However, on the plus side, predators capable of handling a squirrel are not too common.
The savanna and woodland edge habitats of the fox squirrel are precisely the opposite. Acorns, hickory nuts, walnuts, and hazelnuts are all over the place. But savannas and edges are very dangerous places. Predators abound. Coyotes, red-tailed hawks, great horned owls, to name a few, are presences to be reckoned with.
Shaped by the different selection pressures of their favored habitats, according to the hypothesis, the two squirrel species developed different abilities. Gray squirrels became master foragers, able to find and protect an adequate food supply under conditions of scarcity. Fox squirrels got good at avoiding predation. Both species of squirrels are something of a handful--or talonful--for predators. They are quick, strong, and equipped with claws on all four feet, large incisors, and jaws capable of breaking down the hulls of their favorite nuts. So Brown's hypothesis is that in situations where food shortages are exerting the greater pressure on populations, the gray squirrel has an edge. Where predation is the more important factor, the fox squirrels enjoy greater success.
In Illinois before 1950 wild predators, roving dogs and cats, and large numbers of hunters were all out after squirrels. Since 1950 most wild predators are less common--coyotes could be the single exception--and we have more leash laws and inside cats, and hunters are far less common than they used to be. All these factors combine to make food getting--and keeping--a far more critical issue than avoiding predation. So the advantage has shifted from fox squirrels to gray squirrels. Fox squirrels hang on in the city near river corridors (Horner Park), in the lakefront parks, and at Pulizzi's house (near a railroad corridor) where predators may still be around.
Part of a fox squirrel's ability to avoid predators can be attributed to its larger size, but behavior plays a big role too. The fox squirrel is generally regarded as more laid-back than the gray with a gentle easygoing disposition. Grays are high-strung, fidgety, aggressive. In any direct encounter between the two species the fox usually gives ground to the gray.
So shouldn't this make the gray squirrel better able to escape predators? Not exactly. According to Brown, the gray squirrel runs instantly from anything suspicious. The fox squirrel will pause a moment to be sure there is good reason to run. To gauge the effect of this difference Brown suggests that we imagine a martian ecologist studying the effects of automobile predation on humans. Setting up a blind at, say, the intersection of Michigan and Chicago avenues, he sits for two years and records no examples of successful predation by wheeled vehicles on pedestrians. Looks like predation is insignificant. But if he had asked the pedestrians whether their behavior was affected by the presence of cars, they would certainly all have said yes. If you want to cross those streets, you have to be thinking about cars every second.
Just so a gray squirrel, nervous about predators, running first and only looking back once it is 15 feet up a tree, spends a lot of time and energy staying out of the way of fangs and claws. Meanwhile the less excitable fox squirrel is gathering all the acorns in the neighborhood.
I guess if you want to help fox squirrels, let your dog run loose.
A final word about black squirrels: They are just a color phase of gray squirrels, and there is a range of colors from black with some gray to pure black. They can turn up anywhere, but they seem to be more common in the northern parts of the animal's range. Ed Cohen will be interested to know that Ontario is noted for its large numbers of black squirrrels, so maybe the animal on his block did come from there--although it could much more easily have come from here. Aberrant color phases in wild animals are usually selected against by natural conditions. The famous white squirrels of Olney, Illinois, would not survive if they weren't protected by the town. It may be, however, that the disadvantage of being an all-black squirrel is reduced in urban circumstances, so they could become more common in cities than in the countryside. It has been suggested that the greater abundance of black squirrels in the north is because they can soak up more solar energy quicker than paler animals. And maybe they are harder for predators to locate in dark forests.
By the way, fox squirrels also have black phases. Hence their scientific name: Sciurus niger. Seems that the first fox squirrel known to science was black.