Answered by Doug Halford, Wildlife Biologist, INL ESER Program
Bird migration is the regular seasonal movement, often north and south along a flyway, between breeding and wintering grounds. Many species of bird migrate. Migration carries high costs in predation and mortality, including from hunting by humans, and is driven primarily by availability of food. It occurs mainly in the northern hemisphere, where birds are funneled on to specific routes by natural barriers such as the Mediterranean Sea or the Caribbean Sea.
The Arctic tern holds the long-distance migration record for birds, traveling between Arctic breeding grounds and the Antarctic each year – 56,000 miles! Albatrosses circle the earth, flying over the southern oceans. Shorter migrations are common, including altitudinal migrations on mountains such as the Andes and Himalayas.
The fastest long-haul flight would be the Great Snipe—surprising given how plump it can get before its winter migration. But what it lacks in aerodynamism, it makes up for in energy. Without relying on tailwinds that would help it go faster, this stocky bird has been recorded to reach speeds of up to 60 mph for a distance of more than 4,000 miles. It doesn’t even take any breaks and loses half its weight as a result.
Imagine going on a nine-day flight with no time to sleep and nothing to eat or drink. This is the way of the Bar-tailed Godwit; from Alaska to New Zealand, it holds the record for the largest non-stop flight of any bird, flying for over 6,835 miles without rest.
Birds migrate from areas of low or decreasing resources to areas of high or increasing resources. The primary resources being sought are food and nesting locations.
Birds that nest in the Northern Hemisphere tend to migrate northward in the spring to take advantage of burgeoning insect populations, budding plants and an abundance of nesting locations. As winter approaches and the availability of insects and other food drops, the birds move south again. Escaping the cold is a motivating factor but many species, including hummingbirds, can withstand freezing temperatures as long as enough food is available.
How Do They Keep Going?
Some birds eat along the route, but some birds eat more just before migration and store a special, high-energy fat in their bodies. This is necessary because some might not eat for several weeks as they migrate. Most birds that require food during the trip fly by night in small flocks.
Why do geese fly in a V? Scientists have determined that the V-shaped formation that geese use when migrating conserves their energy. Each bird flies slightly above the bird in front of him, resulting in a reduction of air resistance. The birds take turns being in the front, falling back when they get tired. In this way, the geese can fly for a long time before they must stop for rest.
Materials: hair dryer, square block, tape measure, masking tape
- With the tape, mark 2 positions on a flat surface; one for the head of the hair dryer and one for the block.
- Aim the hairdryer at the flat side of the square block and turn the dryer on “high.”
- Measure how far the block moved.
- Repeat the experiment with the dryer blowing on the corner edge of the block. Was there more air resistance on the flat side or the corner edge of the block?
- Try the experiment with a cylinder-shaped block.