Migratory birds travel long distances each year to find abundant food resources, escape unfavorable weather conditions, and find suitable breeding sites.
Every year, migratory birds experience a powerful internal need related to their internal biological clock. This clock, largely regulated by the length of the day (what is called photoperiod), causes a restlessness known as Zugunruhe, or "migratory restlessness." Essentially, the birds become nervous and feel the urge to move at specific times of the year. Hormonal factors also come into play: changes in their levels of hormones, such as melatonin or various sex hormones, trigger these massive migrations. This biological phenomenon drives them to return to specific locations, often the same ones each year, to breed or spend the winter in areas richer in food, thus optimizing their chances of survival and reproduction.
The climate directly guides migrations: when winter approaches, food decreases significantly in certain cold regions like Northern Europe or Siberia. Insects die or hide, and berries and seeds become scarce. Migratory birds then head straight to warmer areas, full of resources at that specific time. Conversely, in spring, when northern regions warm up again, food reappears abundantly. The birds then return in the opposite direction to these territories that have become hospitable again. Some birds even move according to the amount of rainfall, seeking out wetter areas where worms and insects proliferate. Their instinct drives them to follow these variations in climate and food availability to ensure their survival.
Migratory birds first rely on their physical abilities: they accumulate a lot of fat before departure, a true energy reservoir to cover the distance. During flight, they often practice soaring, taking advantage of rising warm air currents to conserve their energy as much as possible. Some species even adopt the technique of V-formation flying, which reduces the effort for each bird by allowing them to benefit from the protective effect of the turbulence created by those in front. Another trick is that they use natural landmarks, such as rivers or mountain ranges, and can orient themselves using the sun, stars, or even the Earth's magnetic field. Finally, their migration is punctuated by regular stops: these breaks allow them to feed, recover, and recharge before continuing their journey.
Every year, millions of birds take to the road to migrate, but this great journey is far from a safe stroll. Along the way, they must face extreme fatigue, violent weather, and a regular lack of food. Many exhaust their energy reserves, and some may even die on the way due to complete exhaustion. Violent storms complicate their journey and can force entire groups to deviate from their path, thereby increasing the distances they need to cover. And then, there are the predators: from raptors to terrestrial animals that seize the opportunity to catch exhausted birds. The light pollution from cities often disrupts their usual landmarks, sometimes leading them into the heart of dangerous urban areas. Not to mention the obstacles created by human activity: glass buildings, antennas, wind turbines... so many invisible traps responsible every year for the deaths of numerous migrants. As for human activities like hunting or the destruction of essential habitats such as wetlands, they complicate their journey even further. In short, migrating quickly becomes complicated and can even become quite risky for a bird.
Migratory birds, through their regular movements, clearly influence the biodiversity of the regions they pass through. They are often important vectors for seeds, helping certain plants grow in distant locations. Their droppings serve as natural fertilizers, enriching the soil and slightly altering plant growth. However, they can also sometimes carry parasites and diseases, leading to negative impacts on local populations of birds or other animals. These migrations also create seasonal spikes where many predators take advantage of the temporary presence of migratory birds, which temporarily alters the entire food chain. Their temporary absence, on the other hand, can reduce pressure on certain species or resources, thus providing valuable respite for some ecosystems.
Some species of migratory birds are capable of flying for several days in a row without stopping, thanks to their exceptional ability to store energy in the form of fat.
Migratory birds use various combined navigation methods (sun, stars, Earth's magnetic field, and geographic landmarks) to find their exact destination each year, thousands of kilometers away.
During migrations, some birds fly in V formations to reduce air resistance, thereby saving up to 20 to 30% of their energy.
The non-stop flight record is held by the red barge, capable of covering up to 11,000 km without landing to refuel or rest.
Currently, the red barge holds the record for the longest recorded non-stop migration. It can fly approximately 11,000 kilometers without stopping, connecting Alaska to New Zealand in just 8 to 10 days of continuous flight.
Some bird species can indeed sleep in flight, adopting short phases of uni- or bi-hemispheric sleep (one half or the entire brain at a time). This ability allows them to cover significant distances while minimizing fatigue.
Most species generally follow similar migration routes each year, but the exact paths can vary. Factors such as food availability, weather conditions, and environmental changes often influence the specific routes taken by migratory birds from one year to the next.
Sure! Here’s the translation: "Yes, climate change significantly impacts migrations. Some species alter their routes, leave their breeding grounds earlier or later, or extend their residency period in areas that were previously only temporarily inhabited. These adaptations can have important consequences for the ecosystems crossed as well as for the bird populations themselves."
Birds use various orientation mechanisms to guide themselves during their migratory journeys. They often combine visual cues (landscapes, waterways), Earth's magnetic fields through a kind of internal compass, and the position of the sun and stars to adjust their trajectory.
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