While we await the region’s autumn rains, the rest of the country prepares for winter. After last year’s ordeal, flocks of snowbirds east of the Rockies are preparing their escape routes.
Some will visit our region. Others will head south.
Our behaviour mirrors a time-honoured tradition begun by our feathered friends eons ago. Scientists recently established that the region’s migrating birds are at heart northern residents that, like their human counterparts, head south to avoid winter.
For years, scientists believed migrating birds first started leaving southern territories to travel northward across and between continents because of intense competition for space and food in the crowded tropics.
But that theory is now turned upside-down, geographically speaking. After analyzing the family trees and territorial origins of sparrows, warblers and blackbirds, scientists found that long-distance migration was twice as likely to arise among bird ancestors from temperate regions as among ancestors from the tropics.
The majority of the species started migrating by moving their winter ranges southward.
As winters warm with changing climate, those temperature pressures will ease. We might see flocks of some birds leaving our region later in the fall or even staying through the winter, as many local Canada geese and humans have done.
In another study, British researchers found that individual birds of some species arrive at their breeding grounds like clockwork at the same time every year.
However, the scientists also found that warming climate at the birds’ northern territories might be shifting the timing of the birds’ migration over time and across populations.
After tracking a flock of black-tailed godwits in Iceland for 20 years, the researchers found that these large, long-legged, long-billed shorebirds now arrive in Iceland about two weeks earlier than they had at the study’s start.
The birds nest earlier in warmer years. Birds that hatch earlier migrate south earlier. This, in turn, can lead to earlier spring migrations, which can position individual birds to better respond to early warm temperatures — if they occur — by mating, nesting and laying eggs correspondingly earlier.
Over generations, the flock’s migration date creeps up.
But temperatures alone don’t account for how some birds are able to migrate immense distances. The amount of energy a bird needs to fuel a two- or three-week flight between North and South America requires changes in biology, too.
University of B.C. researchers found one oddball explanation for how the Audubon’s warbler, a tiny songbird found from the Pacific Northwest to Mexico, became a long-distance traveller.
Most birds either stay put in one region or migrate, but this common warbler behaves differently in different locations.
Northern populations breed, then migrate south for the winter. Southern populations sit tight throughout the year.
The warblers have the same mitochondrial DNA as myrtle warblers, a different species that migrates to the southeastern U.S. and Central America. Mitochondrial DNA is the genetic material of a cell’s powerhouse.
The scientists pinpointed a region near the Utah-Arizona border, where the myrtle warbler’s genes for travelling displace the Audubon’s warbler’s ancestral mitochondrial genes.
Whereas we humans use airplanes or vehicles powered by fossil fuel to travel great distances, birds must store and use the required energy within themselves.
Mitochondria generate the energy that cells need to contract heart muscles, flap wings and do whatever else a bird requires to fly migration marathons.
After an initial mating that introduced the myrtle warbler genes into the stock, subsequent generations of Audubon’s warbler might have taken advantage of the distance traveller’s mitochondria to power their own long-distance migrations.
Winter temperatures influence the seasonal travels of many two-legged creatures — both bird and human. High-energy transport capabilities — flapping flight, airplane or motor vehicle — make those migrations possible.