The emmigration of animals, and birds in particular, is one of, if not the most, amazing events of nature.
Here is a link to a Youtube video about bird migration;
A map depicts the migration of 19 sooty shearwaters that were tracked using electronic tags in a recent study.
The research showed that the birds migrated 40,000 miles (64,000 kilometers) a year, flying from New Zealand to the North Pacific and back. It is the longest animal migration ever recorded electronically.
Map courtesy PNAS/Inset photo courtesy Steve Shunk/USGS
The Mystery of Migration
Mangrove and wetland wildlife at
Sungei Buloh Nature Park
Why do birds migrate?
The reasons are complex and not fully understood. But a simple explanation is food and a safe place to breed. Birds which breed in the summer in the extreme north such as the Arctic benefit from an abundance of food as plants and insect life flourish in the long daylight hours; and because few large permanent predators can survive the harsh winter. Many birds that breed in the Arctic simply lay their eggs on the ground. Being able to fly, they can avoid the harsh winter conditions, and be the first to arrive to enjoy the summer benefits. In fact, some have suggested that the question should be why don’t all birds migrate. Flight gives birds a huge advantage in finding new sources of food and good places to breed, that it is strange that not more birds migrate.
How did bird migration routes become established?
Migration is affected not only by food supply, but also by wind and oceans currents. These make some routes and locations easier to reach. While many birds migrate from northern breeding areas in the summer, to southern wintering grounds (mainly because there is more land near the northern pole than the southern), there are many other migration patterns. Some birds breed in the far south of South America, Australasia and Africa, and migrate to northern wintering grounds. Some birds migrate horizontally, to enjoy the milder coastal climates in winter. Other birds migrate in terms of altitude; moving higher up a mountain in summer, and wintering on the lowlands. All kinds of birds migrate, from large cranes, birds of prey, to tiny hummingbirds. Even flightless birds migrate! Emus move from breeding sites in the rainy season to more permanent water sources in the dry. Penguins migrate in the ocean. Auk babies migrate by swimming until they fledge and can fly! Even birds that spend their entire non-breeding time in flight, such as seagulls, also move around on the ocean to follow seasonal food abundances.
How do birds migrate such long distances?
Birds exploit the winds to their favour so they can go the distance by burning minimal fuel. They may shift altitude to find the best wind “conveyor belt”. Winds at high altitude may blow in the opposite direction from wind on the ground, and usually are blowing strongly. Larger birds rely on thermals (hot air) rising from the ground in the mornings to gain altitude by simply soaring. These birds usually migrate during the day. They may also follow strong updrafts along ridges.
The longest migration is undertaken by the Arctic Tern (Sterna paraisaea). It breeds in the Arctic North in the summer, then flies all the way to the other pole to spend winter on the Antarctic ice pack. The shortest distance between the two poles is 15,000km, but the birds usually travel a more circuitous route and can cover up to 20,000km; making a round trip of 30-40,000km!