One of the most interesting aspects of avian biology is bird migration. Their physical prowess, consistency, and sense of direction are simply astounding. But why do birds annually subject themselves to such physical strain in order to travel such vast distances?
When food supplies become limited in the autumn and winter, birds migrate. Birds may find the summers in the north to be so good that many migratory species decide to nest there.
But in the winter, things become so bad that birds have to migrate south to escape the bitter cold. The global trend is consistent and encompasses a vast array of distinct bird species.
Every year, the globe goes through four distinct seasons, with the degree of difference between them increasing with latitude. Put another way, the difference in seasonal temperatures increases with distance from the equator.
The north pole is closer to the sun in June and the south pole is closer to the sun in December due to the tilt of the earth during its orbit around the sun. The seasons originate from this, which explains why winter occurs in South America and summer occurs in North America.
By crossing the equator and entering the southern hemisphere, birds may dwell in a state of continuous summer. However, long-term migrations like these aren’t usually required. Many birds really migrate just inside the United States and Canada, sometimes not even venturing outside of their own states.
A large number of birds do not make it through the perilous migration route. Even if weather, hunters, predators, and weariness have an impact, birds nonetheless migrate annually like clockwork.
To discover more about the wonders of bird migration, continue reading.
How do avian migration preparations go?
Birds cannot just dive into long-distance migration without training. While certain birds, like barn swallows, can readily eat on the fly, others travel slowly, stopping often to rest and feed. Some birds, nevertheless, finish their whole migration in a single trip, even crossing seas where they are unable to stop.
Continue reading to find out how birds get ready for lengthy migrations.
Dietary modifications and energy storage
Long-distance migrants need to accumulate enough fat reserves to provide them the energy they need to go. Some birds prepare for their migration by virtually doubling their typical body weight.
They do this by eating more food overall and by emphasizing items that will allow them to store fat. Birds are not required to deliberately consider this. On the contrary, hormones cause them to begin eating more.
Not only do birds consume more food, but they often alter their diets as well. For example, songbirds that consume insects often turn their attention to fruits since they may store fat in them.
Changes in the muscles and organs
Certain birds even go so far as to partly shrink and re-absorb organs in order to create way for the creation of new body parts in preparation for migration.
The most well-known example of this amazing preparation is the bar-tailed godwit. These birds have smaller digestive tracts but larger hearts and stronger wings.
This is what they must do to ensure that they are in optimal physical shape for their nonstop 7,000-mile voyage from Alaska to New Zealand across the Pacific Ocean.
Molting
Before setting out on their voyage, migratory birds molt their feathers. Usually, this occurs immediately after their mating season. Migratory birds are better flyers because they have a new set of feathers.
How do birds find their way around?
Every year, species as tiny as rufous hummingbirds must travel hundreds of kilometers to and from their breeding and overwintering habitats, making bird migration an arduous task. As amazing as the physical stamina needed to get the birds there is the capacity to return year after year to the same locations!
Continue reading to discover some of the fascinating ways that birds migrate and navigate.
Both instinct and education
It is believed that birds travel to and from their overwintering habitats using both instinct and sense. Certain bird species must depend on instinct to undertake their initial migration, while others follow their parents to discover the path to their overwintering habitats.
First-time migrants have the simplest navigational strategies; they know to fly in a certain route for a predetermined duration of time. It is believed that they pick up on certain features and maybe even scents along the route, which helps them create a mental map that will enable them to visit the same location year after year.
Magnetic domains
It has long been known that birds can sense direction by using the Earth’s magnetic field. The term magnetoreception refers to this extraordinary sensory capacity.
Although many of the specifics are still unknown, scientists have shown that birds can “see” magnetic lines. The optic nerve travels from the eyes to the brain carrying the stimulus.
There’s another amazing use of magnetoreception in birds. Because of signals from a section of the beak that contains magnetite, they are also believed to be able to sense the strength of magnetic fields. Because of this, birds may be able to create a map of their surroundings by using the differences in magnetic strength.
Direction of the stars
Birds are able to navigate by using the sun’s position as a compass. Birds must, of course, take into account the time of day and even the season to some degree while navigating by the sun since it does not seem to stay in one spot all day.
During the day, the sun is a terrific guide, but what about at night, when birds migrate? Astute investigations have shown that birds can navigate during migration by using the positions of stars.
Rather of memorizing constellations, they navigate by using the positions of the stars that make up the night sky’s axis.
Are birds migratory in nature?
Not all bird species migrate. There may be more or fewer migratory birds than local stationary birds, depending on the temperature and latitude where you live.
The majority of birds visit the Arctic and northern temperate regions during the summer since the winters there are too severe for most bird species to survive. However, the seasonal variations are less severe in more tropical places, where many birds may remain in one place all year round.
Why do some birds travel while others stay put?
Many birds reside in places where the year-round conditions are favorable. If a bird can endure the local weather and has access to a consistent supply of food and water throughout the year, it does not need to migrate.
Certain birds may live very far north without migrating, such as northern cardinals. They have evolved to withstand low temperatures and search for the seeds and plant material necessary for their survival.
Because there is always food available, cardinals can survive, but what about birds that eat seasonal things like insects? Many songbirds, such as warblers, are among these species that are compelled to go southward to warmer climates where insects are still active.
How far do birds migrate?
Depending on their species and the locations of their breeding and overwintering habitats, birds migrate over varying distances.
Certain species may fly for up to twelve thousand miles, while others can only travel a few hundred miles or so throughout their migration. Of all the birds, the Arctic tern is reputed to have the longest migration.
In the world of birds, latitudinal and altitudinal migration are the two most prevalent types of migration. When the seasons change, longitudinal migrants often move north and south. These migrants have a reputation for traveling the farthest, sometimes logging several thousand kilometers annually.
Another excellent illustration of a long-distance migratory is the peregrine falcon. Every spring, these birds may fly an incredible 9,000 kilometers between Argentina and Canada.
Migrations that are inclined tend to cover significantly shorter distances. In the summer, these birds migrate to higher altitudes, and in the winter, they relocate to lower altitudes. Even though they may go in any direction, altitudinal migrants may only cover a few hundred kilometers at a time.
One excellent illustration of a short-distance migratory is the Costa hummingbird. These little birds move, sometimes even staying in California, between the coastal regions of the West Coast and the deserts of the American Southwest.
An unverified hypothesis
Less than half of bird species migrate, in actuality. Climate change is also causing modern migratory patterns to adjust, and as a consequence, departure dates seem to be changing.
Another viewpoint comes into focus when we examine past historical periods during which the earth’s climate fluctuated, such as the Ice Ages. It’s possible that birds migrated toward the equator when temperatures dropped at the poles. It is also possible that some of them moved back farther north or south when the ice period retreated millennia later.
Many of the birds that are recognizable to us today may not have had any need to go to the places where they currently spend portions of the year and which we presume to be their native habitat if not for their forebears.
Skeletal remains also reveal that their predecessors were relatively late evolutionary visitors to the main centers of the human population, having established themselves much earlier in history in what we now consider to be remote locations.
Could it be that contrary to what we humans perceive, the swallow, osprey, goose, and sparrow are not really leaving their ancestral homes, but rather returning there until a far-off future when the climate varies enough for them to live there year-round? Nature is replete with examples of natal philopatry, which is the phenomenon where adults eventually return to the place they were born to reproduce, such as salmon, eels, turtles, and others.
Do birds consider their existence in our neighborhoods to be nothing more than a bother that will eventually be forgotten when the next interglacial era starts?
