Autumn is a time for winding down. The hot summer is behind us, and with the cooler days and shorter daylight hours nature is changing, evoking brilliant colours on the leaves of deciduous trees, changing animal behaviour, and slowly preparing for the winter ahead.
The last of this year’s Western garter snake offspring are just being born. The mating season ends for the North American bison – the calves will be born next May or June – while Barren ground caribou have arrived in their rutting areas and begin their annual mating season. Grizzly and Black bears are searching for denning sites. Early in October, Blackfooted ferret fans will celebrate the third anniversary of the species’ successful reintroduction to Saskatchewan’s Grassland National Park.
And it is bird migration time. Semipalmated sandpipers take flight from the upper Bay of Fundy, an important staging area for this species that migrates to Central and South America. American robins in their second year have developed their adult plumage and are now in-distinguishable from their elders. Trumpeter swans in northern areas travel to their winter grounds in Idaho, Wyoming and Montana where geothermal activity warms pools and streams.
In October and November, thousands of raptors – hawks, harriers, vultures, falcons, osprays and eagles – migrate to the south in huge flocks. Sometimes hundreds of hawks fly together at great heights, averaging speeds of 50 km/h.
But not all birds leave; many overwinter here and stick around to splash a bit of colour across the gray winter canvas. Among them are chickadees, Blue jays, cardinals, and some species of woodpeckers. Chickadees and Gray jays collect and store food when it is plentiful and use these caches when fresh food is not readily available. Other birds band together in foraging flocks or make periodic irruptions (sudden, food-driven temporary increases in the local population of migrant birds) away from their normal ranges when food supplies run low. Look for more about our winter wayfarers in the next edition of Nature Notes.
Winter strategies for wildlife demonstrate how animals deal with the need to conserve energy, store survival food, and adapt to demanding conditions. Many small mammals find temporary hiding places to protect themselves from harsh winter weather. Bats, chipmunks, woodchucks and all native Ontario reptiles and amphibians retreat into dens to hibernate so they can conserve their energy during the food-scarce winter months. In this state, heart and breathing rates slow down, along with body temperature and metabolism. As a result, fewer calories are required and the animals can survive the winter relying on their fat stores alone.
Some animals gather and bury food in the Fall, others feed excessively before winter comes to store extra fat in their bodies. Adaptation examples include insulating fur, change of fur colour to fool predators, and spreading toes or hooves to act like snowshoes. Foxes have extra fur around the pads on their feet and ears, and warm coats to help prevent frostbite. Raccoons and squirrels still scamper around on milder winter days, but take cover when the weather is frigid.
Deer survive in winter by relying on fat reserves they build up over late summer and early Fall. An adult deer can increase its body weight by 20 – 30 per cent before the snow falls. The built-up fat reserves account for 40 per cent of a deer’s daily nutrition requirement. Deer also start eating less in November, gradually reducing food consumption to about 50 per cent of their normal intake. During this time, deer tend to be less active and find sheltered places to keep warm and to sleep.
Some critters simply hibernate, but wasps – at least most of them – do not. As Fall arrives, the queen in a hive dies, along with most of the worker wasps that build and maintain the hive. Only the queen’s daughters – the new queens – live to the following season. A few males survive into the Fall to breed with the new queens before succumbing to the cold. The new queens go into a torpid stage in sheltered areas and emerge in the Spring to start their own colonies to establish the next generations.
The dead of winter, however, does not mean death of wildlife, be that fauna or flora. Life goes on and is usually richest where two types of habitat meet and overlap, such as at the edge of a forest. In their book Wild City, naturalists and authors Doug Bennet and Tim Tiner explain that such overlapping habitats are called ecotones and that the most diverse of them are forest margins, whether they border on meadows, marshes or lakes. In cities, treed fencerows and roadside fringes connected to remnant woods, parkside groves, ravines and greenbelts are also extensions of forest edges.
Most of the native wildlife that has adapted best to cities includes many bird species and mammals that are, by their nature, denizens of woodland margins. Forest edges also offer a place to root for many trees and shrubs that need a lot of sunlight. Besides aspens, poplars and white birch, they include hawthorns, chokecherry, high-bush cranberry, alternate-leaf dogwood, speckled alder and staghorn sumac. Flowers like coltsfoot, wild geranium and spotted jewelweed also proliferate at forest edges, as do honeysuckles, Virginia creepers and wild grapes. Forest edge songbirds include redstarts, common yellowthroats, Nashville warblers, yellow warbles, and mourning warblers. Among the butterflies that hang around forest edges are mourning cloaks, tiger swallowtales, question marks, spring azures and fritillaries.
Good news: a decade after the alien emerald ash borer (EAB) started infecting and killing millions of healthy ash trees across Canada, an imported tiny Asian wasp may rein in the devastation. It lays its eggs in ash borer larvae, killing them before they have a chance to reach maturity and breed. The wasps won’t eradicate ash borers completely but they may help reduce EAB numbers to the point where they will no longer be killing healthy trees. That is good news because ash makes up a large percentage of Canada’s deciduous forest cover and losing those trees to the EAB is disastrous in several ways: not only is there an economic cost associated with the loss of timber, the disappearance of ash from the forest also severely curtails biodiversity because many other species rely on ash forests for habitat and food.
In China, where the emerald ash borer is indigenous, the insect attacks only sick or stressed trees, suggesting that, over time, Chinese ash trees have developed a natural resistance. So far, our native Canadian ash trees don’t have this resistance, but it might evolve over time. It is possible that the EAB will kill 99 per cent of Canadian ash trees and the surviving one per cent may develop a different phytochemistry. They will be the ones that will reproduce, so a healthier ash tree species may evolve in the long run. That, however, will take time – and time is something our ash forests don’t have. So maybe the introduced Asian wasp may come to the rescue.
When you take an autumn hike in the Rouge Valley or on your favourite nature trail, observe the changes in the environment, look for ash trees and for wildlife at the forest edge, and be aware that November 21 is World Fisheries Day. Happy hiking! S.G.
Sources: Canadian Wildlife Federation, Toronto Wildlife Centre, Engadiner Post, Wild City, and field notes.