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.