Most Red-tailed Hawks migrate south in the fall, however some, such as this bird that has been living in London this winter, will stay unless they face sustained, inclement weather. Red-tails, Canada Geese, and Northern Cardinals are among the so-called facultative migrants. Photo by Paul Nicholson.
Every spring and fall, we hear the honking of Canada Geese overhead, and when we look up, we will often be able to see the classic “V” formation of the geese in flight. Even youngsters learn about this phenomenon in school.
So why is it that we can still see some Canada Geese in and around London in the heart of the winter? Shouldn’t they have all headed south months ago?
As it turns out, the Canada Goose is one of the bird species that intuitively engages in some advanced risk management. Migration is often a high-risk activity for birds. The flight is energy intensive, and there are real risks associated with inclement weather, food scarcity, fatal collisions, and predation en route. There are plainly risks associated with staying put as well. Food security and winter weather are two of the greatest risks that birds overwintering in Ontario face. A subset of Canada Geese will accept the risks of staying in Ontario. There will be enough food through the winter to sustain a limited population, and if the weather is inclement for a sustained period of time, the birds still have the option of flying to the south side of the Great Lakes.
Birds that remain in the northern parts of their range as long as their basic needs are met through the winter are called facultative migrants. The Canada Goose isn’t the only facultative migrant in London and Middlesex County.
Each fall, while birding along the north shore of Lake Erie, there will be several days when I witness the migratory southbound flight of thousands upon thousands of Blue Jays. The birds are flying to the eastern U.S. We all know, however, that Blue Jays are frequent visitors to winter bird feeders here, and if you do a local bird watching hike in January, February, or March you will likely hear or see a Blue Jay. The ones that stay behind do so because there is enough food to sustain them.
It surprises some Londoners to learn that the American Robin is a facultative migrant as well. We often think of the Robin as being one of the first signs of spring. In truth, some of these birds can be seen here in all twelve months of the year. To be sure, most do fly south in the fall, but the Robins that stay in Middlesex County will survive on a diet of fruit, berries, and insects if they can be found. If there is a two-week spell of heavy snow and food becomes more difficult to find, they may then fly south to Ohio or elsewhere in the north-east U.S.
The Red-tailed Hawk is yet another facultative migrant.
Birds that are “hard-wired” to migrate are referred to as obligate migrants. This includes most of the Middlesex County nesting bird species such as warblers, vireos, flycatchers, and gnatcatchers.
It has been proposed by Dr. James J. Gilroy, a bird scientist with the University of East Anglia in the U.K., that the since the migration of facultative migrants is more flexible than the migrations of obligate migrants, “facultative migrants may be more resilient to environmental change.”
Another, smaller group of bird species are the non-migrants. Birds such as the Northern Cardinal, the Black-capped Chickadee, the Downy Woodpecker, and the Red-bellied Woodpecker simply stay here year-round. They have physiological adaptations that serve them well in the face of both hot and cold temperatures.