Bird species primarily migrate south in winter to seek food sources and safe nesting locations.
All around the world, as autumn arrives, flocks of birds can be seen flying south in preparation for a harsh winter. This scene is so common that you might hardly notice it, yet it represents a remarkable journey covering hundreds of thousands of miles.
Driven by instinct, these migratory birds can annually complete an astonishing distance. But why do they undertake this journey? The obvious answer is to escape the freezing winter, but there are many underlying reasons.
Do all bird species migrate south in winter?
While it may be difficult to find birds in your area during winter, this does not mean that all bird species migrate at this time. This behavior is characteristic of certain species known as migratory birds.
Only about 40% of bird species regularly migrate south in winter. However, the migration story is quite complex; some species migrate locally, some head south, while others stay put.
Seasonal migration is the most common type of migration in birds.
Migration does not necessarily mean flying south. Some species choose to move to different altitudes, living in higher regions during summer and descending to lower areas in winter. Others migrate sporadically in groups to find food, while some species migrate to molt, selecting safer locations to wait for their feathers to regrow.
Nonetheless, seasonal migration is indeed the most common type of migration in birds. And it is not solely related to cold weather.
Why do they migrate?
Bird species are often quite skilled at surviving harsh weather conditions. They can endure the cold and biting winds of winter, but finding enough food and resources is a different story. Birds primarily migrate south in winter to seek food and nesting sites.
During winter, food sources for birds gradually diminish. Insects and other food supplies decline during this period, making it difficult to find safe nesting locations. They fly south to warmer regions, where food is abundant and shelter is easier to find.
Some bird species do not migrate far, but for those that prepare for a long journey, the trek can be grueling yet incredibly impressive. Thousands of years of evolution have honed their migratory instincts, and scientists are still striving to understand the factors that dictate this migration. Genetic factors play a role, but changes in temperature and sunlight also seem to help birds know when to migrate and where to go.
Scientists do not fully understand how birds can navigate so accurately. Young birds often undertake their first journey alone and can return precisely to where they were born the following spring.
Researchers believe that some sensory abilities aid birds in this process. For example, birds can sense the Earth’s magnetic field, and their sense of smell also contributes to their navigational skills.
Additionally, long-distance migration is essential for the survival of bird species. Studies show that birds with long migration distances tend to have higher survival rates through winter compared to those that migrate shorter distances.
Why don’t birds settle permanently in the South?
Baltimore Orioles are common in North America. After breeding in the Northeast, they migrate to Florida, Mexico, Central America, and South America for the winter. (Photo: Gulo in Nature).
However, once they reach warmer climates with abundant food, why don’t these birds settle there permanently and instead return to the Northern Hemisphere in summer, given that this back-and-forth journey consumes a lot of energy and poses numerous risks?
Scientists explain that while the South has plentiful food supplies, it is not a paradise. The threat from predators here is much greater compared to temperate environments.
The trade-off for tropical birds is that they can lose up to 90% of their nests to predators, compared to a loss rate of 50% or less for birds in temperate habitats.
Moreover, migratory birds also have to compete directly with native species. Additionally, the warmer climate is also ideal for the survival and spread of infectious diseases and parasites.
To take advantage of the optimal living conditions in both regions, birds have developed a truly perfect strategy.
These migratory birds time their return to the North for spring – a time when food resources explode, offering numerous seeds, fruits, and insects. On this return journey, they will utilize these resources for breeding.
Furthermore, spring and summer in the North have significantly longer days compared to nights, giving birds more time to forage to feed their growing young.
Additionally, as they return north, the populations of their natural predators have significantly decreased following the harsh winter. Therefore, migratory birds can enjoy a safer breeding season.
