Migration

[fredpuli47]

Has anyone ever found an explanation for apparently inexplicable migration ? I'm thinking of humming birds that migrate as far as Canada and seabirds that migrate thousands of miles almost from one pole to the other. Surely food can't be the reason since the birds must have nectar far nearer than Canada or food in the oceans without travelling almost the length of the Earth. And mating and nesting sites can hardly be absent en route. Or are those false assumptions?

[squarebear]

I thought it was to do with temperature?

[stewey]

Some information here.

Non-stop Flights

Many Ruby-throated Hummingbirds travel more than 2,000 miles to go from Panama to their breeding destination in Canada. People wondered how the Ruby-throat could cross the Gulf of Mexico without stopping to refuel, a minimum trip of ~500 miles (the shortest distance across the Gulf).

To answer this question, R.C. Lasiewski conducted a study in 1962, The energetics of migrating hummingbirds (Condor 64:324). As a result of his experiments with hovering hummingbirds in metabolic chambers, Lasiewski concluded that a male Ruby-throated hummingbird, weighing about 4.5 g, of which 2 g was fat, could fly nonstop for 26 hours, consuming the fat at the rate of 0.69 calories per hour.

At an average speed of 25 mph per hour (40 km/hour), the bird's flying range would be about 606 miles (975 km) - easily enough to span the Gulf of Mexico.

In a more recent study, Calder and Jones (1989) using arrival and departure masses and rates of gain from Rufous Hummingbird banding data, determined that a 747 mile (1,202 km) flight of a Rufous appears to have been possible. At an airspeed of 43 km/h, the Rufous was able to travel 747 miles in 28 hours or two 373-mi (601 km) legs in 14-hour days apiece, depending on unknowns of tailwinds & successful refueling points.

Therefore, on its 2,700-mile journey from Mexico to Alaska, a Rufous Hummingbird will stop at least 4 times to refuel.

[jomifl]

Some animals carry out apparently pointless migrations because millions of years ago the migration was benificial in some way and over the intervening years the original reason for the migration has disappeared, but the animals keep on doing it because it is instinctive.

[wildwood]

Migration is a matter of subjective observation. Does a bird live in Africa and migrates to Europe to breed because Africa is too dry and the insects are then rare, or does this bird live in Europe and goes to Africa in the colder season because insects dry up there.

Migrations are undertaken for food, or overwintering to escape the worst of their normal habitat. Some birds only move a couple of hundred miles. The Arctic tern does a complete Pole to Pole trip every year and lives its complete life in lightness - being so small it can not survive the long (and dark) winters on the Pole.

The likes of Hummingbirds must find flowers that allow each individual species' beak to extract nectar. Their migration is gradual as they need to tank up often. By the time they reach their destination the place they left would be without flowers to suit their bills.

Migration is not a phenomenon exclusively exercised by birds. Many insects and mammal species also move about to follow the food availability.