|fwg is a long-term project of the ottawa field-naturalists' club|
Grey squirrels (Sciurus carolinensis) at the FWG
by Christine Hanrahan
Eastern Grey squirrels (Sciurus carolinensis) may be, if not the most ubiquitous, certainly the most visible animal in our towns and cities of eastern North America. So closely associated are they with urban areas, that it comes as a surprise for many to also find them in more natural settings. These animals are quite clever and definitely ingenious. Anyone who has maintained a bird feeder and tried to keep squirrels away knows this, as even "squirrel proof" feeders are often no match for these animals.
They are adaptable and creative in their use of both food and shelter, and it is these qualities, endearing to some of us, that also makes them unwelcome to others. Perhaps one of the biggest reasons they are disliked is simply that they are common. We seem to devalue the ordinary in life and emphasize the rare or unusual. And this is too bad, for a creature as "common" as the grey squirrel can make a fascinating subject of study.
One of the largest tree squirrels in eastern North America, greys weigh in at about 500-520 g (Banfield 1974, Forsyth 1985). They are roughly 50 cm in length, half of that being tail. And the grey's tail is very important to its overall health and well-being. Not only does it help the squirrel balance in the most precarious of places (running along hydro wires, for example), but as Woods (1980) says, "it also serves a number of other purposes, acting as a parachute, a signal flag, a sunshade/umbrella, and a warm wrap." Around my house this winter of 2007, there are several squirrels with completely naked tails, although their coat looks healthy. Will this make it difficult for them to survive a prolonged cold spell?
This species, like others of the squirrel family at FWG, is diurnal, with greatest activity early in the morning and late afternoon. However, in late summer and fall they are busy all day, searching for and caching food to tide them through the coming winter.
Grey squirrels have a melanistic (black) colour phase, which gives rise to the mistaken belief that they are two different species. Banfield (1974) suggests that there must be a reason why more grey squirrels in the northern part of the range are black while those in the southern part are usually grey. He speculates that the gene for the melanistic phase "must carry with it some unknown northern adaptation." Forsyth (1985) adds that perhaps the black coat "acts as a kind of solar heater." In the southern US, there are very few black squirrels and sources from the southern states consider the melanistic phase rare to non-existent there. In the times I've travelled in the south, I can't recall ever seeing a melanistic grey squirrel. There are further colour variations, with some grey squirrels sporting a reddish cast to their coats, and some black phase ones with a red tail. I've seen both of these variations at the FWG.
The grey squirrel's natural habitat is deciduous woodlands, particularly those rich with nut trees such as oaks (Quercus) and beech (Fagus grandifolia). They have readily adapted to urban settings such as backyards and parks, and are the one wildlife species known by almost everyone. Native to eastern North America, this species was introduced out west in the early years of the 20th century, and is now quite common in BC's Lower Mainland. It has also been introduced into Britain, to the detriment of the native red squirrel (Sciurus vulgaris), which has been reduced to small, isolated populations. Here in Ottawa, the eastern grey squirrel is near the northern limit of its range.
Although adept on the ground, grey squirrels are primarily arboreal. They are remarkably acrobatic and leap through the air, from tree to tree, with the greatest of ease! Every so often, however, they miscalculate and fall, sometimes landing with quite a thump. I've watched them pick themselves up in one swift, graceful movement and scurry up the tree in double-quick time. Occasionally they remain immobile for a few seconds, perhaps momentarily stunned. They are also very good at climbing buildings, particularly those made of brick which gives them a good surface to grip.
This species is almost as vocal as the red squirrel (Tamiasciurus hudsonicus), and when they get going they can raise a ruckus. They have a wide range of vocalizations, some very soft, some only given under certain conditions. The most commonly heard sounds are a sort of "clicking," given when agitated, and what Woods (1980) describes fairly accurately as "a series of rasping whicks." Next time you hear either of these sounds, watch the squirrel. You'll see that not only does its tail flick furiously, but its whole body may also vibrate with agitation. Surely this behaviour gave rise to the slang term "squirrelly" to describe someone acting in an irrational, agitated, or odd manner.
Grey squirrels are great tree-planters. Although they manage to find many of their cached seeds and nuts, many more remain undiscovered, the source of new trees. We certainly benefit from their tree planting activities at FWG. Many new red oaks are popping up all over the place and, thanks to squirrels, our walnut trees have substantially increased in number. Between 2002 and 2004, an inventory of walnut and butternut trees at the FWG revealed 43 trees - 11 butternut and 32 walnut (Crook 2004). In the summer of 2006, another inventory was done. While 5 new butternut trees were found, an astonishing 33 additional walnut trees were located, doubling the number since the last inventory (Annie Belair, FWG Management Committee, personal communication).
The biggest threat to grey squirrels is humans. Hunters shoot millions each year, usually for "sport" or their fur, but sometimes for food, particularly in the southern states. Cars kill thousands annually along roads in the Ottawa Valley and elsewhere. At the FWG, dogs, foxes (Vulpes vulpes), and raptors are the biggest predators, although in other areas, raccoons (Procyon lotor), mink (Mustela vison) and weasel (Mustelidae) will also take them.
According to several sources, the size of the grey squirrel's home range depends on sex. That is, females are said to occupy "home ranges of approximately 5-15 acres" (2-6 ha) and males "between 50 and 55 acres" (20-22 ha), particularly in summer months (Banfield 1974). Population density is considered to be, on average, "30 to 75 animals per hundred acres" (40.5 ha) (ibid). Woods (1980) suggests that suitable habitat may have one squirrel per hectare. But clearly a number of other factors influence density and home ranges.
There are perhaps between 10 and 12 grey squirrels at the FWG, with a temporary summer increase when the young emerge. This gives an average of about one squirrel per half hectare on our 5-ha site. In some years, numbers seem considerably less than this, occasionally higher. In my notebooks for 2003 and early 2004, I noted the scarcity of grey squirrels that fall and winter and the almost daily presence of foxes. Several times, FWG volunteers saw a fox kill and drag away a grey squirrel. No surprise then, the dearth of squirrels during that period.
As with most animals in the wild, population density of grey squirrels is tied in part to food supplies. Their favoured food - walnuts, butternuts, and acorns - are not produced in abundance every year. When these staples are scarce, squirrels must find other food locally, disperse to other areas, or starve. And even if they don't starve, poor-quality diet will leave them susceptible to disease and parasites. At such times, there are too many animals for the available food. However, in urban areas where bird feeders are common and a wide variety of other shrubs and trees grow, cyclical reduction of some food sources probably does not have the same impact. Food sources at FWG, although ample, will fluctuate, and competition with other animals, in particular red squirrels, can be a factor influencing numbers in the garden. However, with the Arboretum right next door, there is definitely an ebb and flow between that site and ours.
Like many Sciuridae, grey squirrels are omnivores; although their preferred food is nuts, their diet is varied and seasonal. They occasionally take birds' eggs and some insects, and will gnaw on bones for calcium. I have seen them chewing on dog bones left on my back deck, competing with red squirrels for the pleasure. Banfield (1974) notes that females are reported to "carry bones to their nest to eat during pregnancy, possibly because of a deficiency of calcium."
Summer, and especially fall, are times of plenty with nuts, berries and seeds in good supply. Spring and winter, however, can be lean and this is when they resort to other less-favoured and no doubt less-nutritious food, to stay alive.
Grey squirrels can have two litters a year with an average of 2 to 4 young born each time, but Forsyth (1985) believes that not all females breed twice. At the FWG and Arboretum I begin noticing young squirrels around early June. If there is a second litter, I confess I haven't noticed, although by late summer I'm usually focused on other things.
Much has been written over the years about the natal site of the grey squirrel. Some sources indicate that cavities are used exclusively, others say leafy nests or dreys. It is most likely that the female squirrel prefers cavities, which are safer, drier and warmer, but not always available. When this is the case, the familiar leafy nests high up in trees are used. I've examined a number of them over the years, and have found them quite substantial and heavy. They are usually well made of tightly packed leaves, and lined with a variety of shredded material including vines and grasses, often with a mass of twigs on the bottom. They look like they would provide a warm, cosy nest to raise young. If possible, they will utilize an abandoned crow's nest, adding twigs to the structure and then building their dreys on top. This gives them an even more secure platform. But when stick nests are not available, they will lodge their dreys in the forks of trees to help hold them in place. Both deciduous and coniferous trees are used, but around the FWG, most are in deciduous trees.
Tree cavities big enough for grey squirrels, are typically found in relatively mature trees. At the FWG trees are generally younger (smaller) than in the Arboretum, and cavities are fewer. However, if there are bird boxes large enough, grey squirrels will sometimes use these. I've been able to look at only a few grey squirrel cavities. Those I have seen, have been thickly lined with quantities of leaves mixed with some grass and strips of bark.
If individuals escape predators, cars, and starvation, they can apparently live quite a long time in the wild, up to 6 years, sometimes considerably more (Forsyth 1985). This contrasts with the eastern chipmunk (Tamias striatus) and red squirrel who may live 1 to 3 years.
Winter is a time of such hardship for so many animals that you wonder why they don't all just pack it in and hibernate for the duration. Grey squirrels, like their smaller cousin the red, are active all winter, although they may stay inside their dens or nests for a few days in really bad weather. They prepare for the wintry days to come by packing on the fat, growing a thicker coat and stockpiling food. Unlike red squirrels, they don't hoard their food in one spot, instead dispersing it across a wide area, a method called "scatter-hoarding."
The sight of grey squirrels industriously digging a small hole, depositing the nut, and then carefully patting the earth back into place is so familiar as to elicit no comment. Yet this is a remarkable activity and an act of faith. How does the squirrel know where that particular nut is buried in such a large area? We would have trouble relocating it again without resorting to flagging tape, a GPS, or some other method. So, how do they do it? Considering how vital it is to their winter survival, relocating these nuts has to be more than chance. It seems that greys have a very highly developed sense of smell which enables them to sniff out these stores, even under the snow (Banfield 1974, Lawniczak 2002). However, as we saw above, not all nuts are found again, and those left buried are the squirrel's contribution to tree planting initiatives. Small scrapings or holes in the earth, or soil-covered holes in the snow are a sign that a squirrel has been busy digging up its food.
In addition to an adequate food supply, a warm shelter is vitally important for surviving cold weather. In late summer through fall, grey squirrels begin working on their dreys. They often refurbish the ones used in summer, but will also construct new ones, especially if their old ones have fallen down or been removed. They will nip off branches complete with leaves and incorporate themn into the nest, but more often they gather fallen leaves.
Grey squirrels are intriguing little animals. If you have any stories to share about these creatures, please e-mail me at firstname.lastname@example.org