The image of geese heading south in V-shaped flocks is perhaps the classic picture of migration, the large-scale annual movement of migratory birds between their summer breeding habitat and their winter non-breeding grounds.
Of the 650 species of birds that breed in North America, more than half are considered migratory birds.
Why do migratory birds travel
Migratory birds travel to move from areas of low or declining resources to areas of high or growing resources, and the basic resources that are searched for are food and nesting sites, and migratory birds
that nest in the northern hemisphere tend to migrate north in the spring to take advantage of the increasing numbers of insects and emerging plants and the abundance of Nesting places.
As winter approaches and the availability of insects and other food declines, migratory birds move south again.
Fleeing from the cold is a motivating factor, but many species, including hummingbirds, can tolerate freezing temperatures as long as an adequate supply of food is available.
While short-distance migration may have evolved from a fairly simple method of foraging, the origins of long-distance migration patterns are more complex.
They have evolved over thousands of years and are controlled at least in part by the genetic makeup of migratory birds, and they also incorporate responses to weather and geography.
Migratory birds winter in the tropics. It seems strange to imagine leaving the habitat and embarking on a migration north.
Why make the arduous journey north in the spring? One idea is that over many generations the ancestors of these tropical birds spread north from their tropical breeding sites, and
the seasonal abundance of insectivorous food and greater day length allowed them to raise more young (4-6 on average) than their home-dwelling tropical relatives (2-3 in average).
As the breeding grounds of migratory birds moved north during periods of glacial retreat, the birds continued to return to their tropical home where wintry weather and reduced food supplies made life more difficult.
warblers, orioles, and swallows that have evolved from forms that originated in the tropics.
What motivates migratory birds to migrate
Migration can occur due to a combination of changes in day length, lower temperatures, changes in the food supply, and genetic predisposition.
For centuries, people who kept migratory birds in cages have noticed that migratory species go through a period From restlessness each spring and fall, it rises frequently toward one side of its cage.
German behaviorists have dubbed this behavior migratory restlessness, meaning migration disorder. Different species of birds and even segments of populations within the same species may follow different migration patterns.
How do migratory birds navigate
Migratory birds can cover thousands of miles on their annual journeys. Migratory birds often travel the same route year after year with little deviation.
First-year birds often migrate for the first time alone, and somehow they find their winter home even though it has not been seen.
The secrets of migratory birds' amazing navigational skills are not fully understood, in part because migratory birds combine several different types of senses when navigating.
Among the features that are seen during the day, there is even evidence that the sense of smell plays a role, at least for the homing pigeon.
Some species, especially migratory birds such as water geese and cranes, follow preferred paths in their annual migrations.
These paths are often associated with important stopping sites that provide food supplies necessary for the survival of the birds. Small migratory birds tend to migrate on wide fronts across landscapes.
Recent studies have revealed that many Many young birds travel different routes in spring and fall, to take advantage of seasonal patterns in weather and food.
Risks facing migratory birds
Undertaking a journey that can span a round trip of several thousand miles is a dangerous and arduous task, an effort that tests the physical and mental capacities of migratory birds with
the physical stress of the journey, lack of adequate food supplies along the way, bad weather and increased exposure to predators all. Factors that increase the risks of flight.
In recent years, distant migrants have faced an increasing threat from communication towers and tall buildings.
Many migratory bird species are attracted to the lights of tall buildings, and millions are killed each year in collisions with structures.
and wintering sites. Once identified, steps can be taken to protect these key sites. and conservation, and each spring approximately 500,000 sandhill cranes and some endangered screech cranes use the Central Platte River Valley in Nebraska.