Have you ever seen flocks of geese flying south in the fall? Have you heard them honking? Have you wondered why they are flying in a formation that looks like a “V”? Have you wondered where they are going? They, like many other birds, are migrating.
The word migration comes from the Latin word, migratus, which means “to change.” The word has special meaning when it refers to animals. Migration is the movement of an animal from one region, or habitat, to another. This happens at regular periods of time, and during a particular season. Animals migrate in order to breed, grow, find food or avoid cold weather. For birds, this occurs twice a year. They migrate in the spring and again in the fall.
What Makes A Bird, A Bird?
All bird species have feathers. There are several other characteristics that birds share, but feathers are the only characteristic completely unique to birds. Many might say that it is flight that makes birds special, but did you know that not all birds fly? Emu, kiwi, cassowary, penguin, ostrich and rhea are birds that don't fly. Some birds swim, like the penguin, which does its flying underwater. Learn all about flightless birds.
Birds have many interesting adaptations to benefit their life in the air. They have lightweight, yet strong, bones and beaks, which are adaptations to reduce weight for flying. Birds have incredible eyes, ears, feet, and nests. We enjoy listening to the songs of birds. Discover more about birds.
Why Do Birds Migrate?
Birds seek out places that have warmth, food and are safe for breeding. In the Southern Hemisphere, especially in the tropical climates, it is warm enough — since there is little change in the length of the days from month to month — that birds are able to find an adequate food supply year round. The steady daylight gives birds plenty of time to eat each day, so they don't need to go someplace else to find food.
Conditions are different in Northern Hemisphere countries like the United States and Canada. During the long days of the northern summer, birds have more hours to feed their young on the abundant insect population. But as the days shorten during autumn and food supplies become scarce, some birds migrate south.
Not all birds migrate. There are some species that manage to survive winter while staying in the Northern Hemisphere. Typically, familiar species such pigeons, crows, ravens and blackbirds stay put all year round.
Permanent residents are non-migrating birds who remain in their home areas all year round.
Summer residents are migratory birds that move north in the spring, nest during the summer, and return south in the fall.
Winter residents are migratory birds who fly south for the winter.
Transients are migratory species who nest farther north than our neighborhoods, but who winter farther south. We only see transients as they are passing through.
When Do Birds Migrate?
Each species migrates at a certain time of year and time of day. Some are very irregular in their migration patterns. Some species start their migration south in early July, and some don't migrate until the weather gets too harsh or food becomes unavailable later in the fall. Experiments show that the length of the day stimulates migration. In spring, you might see migrating birds as early as January in Florida!
Where Do Birds Go?
Many species migrate very long distances. The most common pattern is that birds migrate to the temperate or arctic Northern Hemisphere to breed in the summer and migrate south to warmer regions for the winter. There are four main flyways, or migration routes, in North America that most birds follow between their summer and winter locations.
Migrating birds follow certain traditional migratory routes and pass through at predictable times. These routes tend to avoid land forms that might block their way, such as mountains, or water. For soaring birds, such as ospreys, eagles, vultures, and hawks these routes follow paths that take them by areas that generate hot air funnels to rise up from the land. They use this hot air, known as thermals, to soar. By spiraling up a thermal and gliding down to the next one, they save energy needed for long journeys.
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. This allows them to eat during the day, and avoid some predators.
How Do Birds Find Their Way?
Navigation is complicated because it requires that birds know three things: their current location, their destination, and the direction they must take to get their destination.
Some birds use the sun and the stars to navigate. Some also use the sighting of landmarks like rivers, mountains or coastlines. Some might use smell, while some might follow other birds in the flock. But birds can still navigate on cloudy days and fly across the ocean where there are no landmarks. So how can they do this?
Scientists have come to believe that birds monitor the earth's magnetic field using tiny grains of a mineral called magnetite that are located in their beaks. The iron-containing mineral might act like a compass. Other scientists think that the birds can actually see the magnetic field with their eyes. Not all is known about how birds find their way, but they probably use more than one method. Learn more about bird navigation.
So Why Do They Fly In A V Formation?
Flying in that V formation is not an accident. Large birds such as geese and ducks fly in this formation to reduce the effect of friction on their wings. This allows the birds to fly further and more efficiently than a bird flying alone by itself.
There is a 70% increase in efficiency when flying in V formation. The lead bird and the last birds flying farthest back in the V work the hardest, while the birds in between benefit from the flapping motion of the other birds.
In addition to improving their flight, this formation also benefits the communication among the birds. This formation places the birds close together, allowing them to hear and see one another. They honk information to each other (or quack or whatever sound they make) and can watch over one another to keep together.
What Are The Dangers Of Migration?
Sometimes birds must fly across harsh habitats such as deserts, where there is little water, or oceans, where there is no place to land and little food to eat.
Even if they find food and water, they must land to be able to take advantage of the opportunity. This means putting themselves in danger of becoming someone else's food.
There can be many predators along the migration route. Depending on the size of the birds, they can find themselves in danger from cougars, foxes, wolves, humans, or many others. Some birds can actually be attacked by larger birds while in flight. Sometimes stormy weather may make the trip difficult and cause death in severe cases. And occasionally birds have been known to fly into the path of airplanes. This can be dangerous to both bird and airplane.
How Do Ornithologists Study Birds and Migration?
Bird banding image courtesy of fws.gov
Bird banding or ringing is one method used to study wild birds. Scientists attach a small, individually numbered metal or plastic ring to a bird's leg or wing. They also use special nets known as mist nets as a way to capture birds. This way they can capture and re-capture the same individual bird and measure and weigh it and gather other important information over time.
The Pelican Network has some excellent photos of that process. Sometimes scientists use satellite tracking to follow birds on their migration routes. The U.S. Geological Survey offers a brief description of this technology. NASA also explains how radar can teach us about bird migration.
Birdwatching
Birdwatching is the second largest hobby (gardening is the first) in North America with over 31 million participants. People all over the world follow and watch birds and their behavior. They learn to identify birds by their song and by their behavior. People do it for fun, but if you study birds as a career, you are an ornithologist. Learn about birdwatching adventures you can have at Visit Idaho or BirdingPal.
You might want to explore another Science Trek topic and become familiar with Birds of Prey.
If you love birds and think that this might lead you to a future career, take a peek at the job of an ornithologist at Seattle's Burke Museum.
Fascinating Facts
The Arctic Tern has the longest known migration route. It flies about 22,000 miles each year between its breeding grounds in the high Arctic and its winter grounds in the Antarctic.
The swallows of Capistrano have been known for their special migration habits. Cliff swallows flew to the San Juan Capistrano Mission in California and arrived every year on March 19th. On that date since the mission was built in the late 1700's, people have watched as hundreds of birds arrived on their migration from Argentina. Then they left again on October 23rd just as they came in — all together as a flock. The swallows probably came to this general area even before the mission was built, but no one was there to see it happen. In recent years the birds have stopped this annual trip. Scientists are trying to determine what has made them miss their appointment.
Birds can fly at speeds ranging from 20 to 50 miles per hour. Larger birds fly faster than smaller birds. If the flock flies for 10 hours a day, then they can fly about 400 miles a day!
Radar studies show that most flight occurs at less than 10,000 feet, but some birds have been recorded flying as high as 27,000 feet! Birds on long-distance migrations fly at higher altitudes than those who fly short-distances.
