It’s getting near that time of year when Canada’s bird population begins to migrate south again after their summer sojourn here in the north. Birdwatching has become very popular in recent years and often leads to many questions, especially for the newcomer to the activity. One being, “Gee, I wonder why birds migrate back and forth in the first place?”
Let’s find out.
A Two-Way Trip
A recent article in The Globe and Mail reported: “Spring migration, winding down to retirement and the pandemic made a birder out of Diana Gibbs.
In May 2020, the Toronto resident went with a bird watching friend to the park out on the Leslie Street Spit that sticks out into Lake Ontario. Ms. Gibbs, now 66, was beginning to retire from her career fundraising for human rights and social justice organisations.
‘The woods were just alive with sound,’ Ms. Gibbs says. ‘It was really quite striking … a memory that stayed with me.’
Ms. Gibbs joined the legions of Canadians who have discovered the joys of birdwatching, a flexible and addictive hobby that’s grown at a spectacular pace in popularity during the pandemic.”
Fly Away, Fly Away
This emerging fascination with bird migration is all well and good, but it begs the question of why birds migrate in the first place. We decided to investigate.
When spring arrives and we head into summer, a good number of birds chased south by our cold winters return to brighten our surroundings. This annual migration is caused by a desire to return to the place where they were born. But is that the only reason for the dangerous journey? Most of the birds that hatch their young in Canada spend part of the year in Mexico, Central America, South America or the Caribbean.
Some warblers remain for only three months in the Canadian forests where they hatched, spending six or seven months in South America and travelling for two or three months between the two destinations in the spring and fall. Other species such as the snow goose, hummingbird and heron spend only a few months in the north to nest before they travel south for the winter.
The reasons why birds migrate are open to a certain degree of conjecture, so to simplify matters somewhat we have summarised The Basics of Bird Migration: How, Why & Where from Birding Nirvana.
Two Theories Attempt to Explain the Phenomenon
In the first theory, it’s believed that some migratory birds such as plovers and sandpipers were originally from the northern latitudes but were forced to migrate south during the Pleistocene period (between about 2,580,000 and 11,700 years ago) as glaciers covered the northern hemisphere.
Taking advantage of the retreat of the glaciers about 10,000 years ago, the birds returned to their place of origin to nest. The winters were colder than they had been before the last Ice Age, however, so the birds migrated south at the end of each summer.
The second theory has it that some other migratory birds originated in the tropics. This would be the case, for instance, for hummingbirds, flycatchers and warblers. The abundant food and favourable climate of the tropics caused overpopulation and prompted the birds to move elsewhere.
The retreat of the glaciers encouraged them to move northwards to have their young. Migration had an unexpected advantage, as well. A study has shown that as the migratory birds moved to increasingly higher latitudes, their chances of escaping predators increased.
With each degree of latitude northward, the risk of predation of the birds’ eggs would be reduced by 3.6 percent due to the gradual reduction in the number of predators as one moves northward. This advantage would explain why birds would make the exhausting and risky trips, traversing entire continents to raise their offspring in peace.
Migrating north would have been a way to guarantee having a larger family which, to a certain extent, is an instinct they share with us.
If you’re contemplating becoming or already are a bird watcher, you may be interested in the following two blogs we published back in 2018. Birds of a feather – Part 1: Getting started with bird watching and Birds of a feather – Part 2: When and where to go birdwatching.