Most are familiar with flocks of migratory birds soaring through the skies in autumn and spring. But what do we know about them apart from the fact they migrate? We've dug up some astonishing facts for you.
With World Migratory Bird Day coming up on May 9, we started wondering about these feathered creatures and how even the tiniest of birds manages to make the sometimes perilous journey to its wintering grounds. Here's what we found out. Feel free to add more surprising facts in the comments.
We all know just how arduous a long-distance trip can be whether by train, boat or airplane but that is nothing compared to what birds do to reach their winter habitats. The Arctic tern makes thelongest journey
, flying on average 44,000 miles (70,900km) during its annual migration from pole to pole. The bird travels from Greenland to the shores of Antarctica and back to its breeding grounds in Greenland.
The longest recorded journey for a tern was over 81,600 kilometers (50,000 miles) - a distance equalling more than three times the earth's circumference. The bird doesn't fly straight south, however. Instead, it travels along West Africa's coast, crosses the Atlantic ocean and flies over South America to its final destination.
Many on the move
About one-million starlings migrate through Rome during autumn and winter time and describe beautiful patterns in the sky before spending the night in the trees by the Tiber river
Given the exhausting distances involved, you'd think such mind-boggling migration patterns were rare but far from it In fact, 2,000 species of bird - 20 percent of all known species - make regular seasonal movements.
Dangerous air transit
Birds manage to make such mammoth journeys despite various threats, including those posed by humans. In the Mediterranean region alone, millions of migratory birds are hunted and captured each year with guns, nets or twigs covered in adhesive bird lime.
At least two million are said to be caught in Cyprus each year but Egypt tops the list with 140 million birds being caught yearly on their way from Europe to Africa. On the way back they are also hunted in countries such as Albania, leading to population declines because fewer birds get to breed.
Humans have also affected birds' migratory patterns. For instance, overgrazing in the Sahel - a grassland region on the southern edge of the Sahara where millions of hungry birds dine after crossing the immense desert - has caused plants to disappear and the area to dry up. The Sahara is now much wider and some birds, such as sand martins find it much harder to cross. Fewer sand martins visit Europe compared to 50 years ago.
Green energy is usually regarded as something good but for birds it can also be dangerous. A solar plant in the United States uses mirrors to focus sunlight onto a receiver to generate electricity but it’s affecting birds too.
Due to the reflected sunlight, the air above the solar plant gets hot, so hot that within the first year of operation about 500 birds flying over it got toasted by the heat or solar flux; another 500 birds died following collisions with the plant.
Wind turbines and power lines also pose a threat to migrating birds through collision or electrocution.
The problems for migratory birds caused by the expansion of various means for generating and distributing energy, inspired the initiators of World Migratory Bird Day to make this year's theme: "Energy - make it bird friendly!"
No map or compass needed
Migratory birds don't rely on the shape of a landscape for orientation but instead navigate with the help of the earth's magnetic field. This system is practically flawless but humans have disrupted it. Researchers have found that even weak electric fields can affect a bird's ability to navigate.
Before they set off on their long journeys, many migratory birds enter a state of hyperphagia, where hormone levels compel them to put on weight so they can use the stored fat for energy while traveling. Some birds double their body weight before migrating.
Restless, even in captivity
Sand martins fly south to South America, southern Africa and south Asia in winter but even birds in capitivity are restless during migration season
Even birds raised in captivity and have never had the opportunity to migrate are observed to become restless during the migration season. Researchers saw the birds trying to fly in their natural migration direction and also found corresponding traces in the cage's sand.
Engraved into history
Coins usually feature depictions of famous people or historic buildings but as an old Indian coin collection has shown migratory birds can also make it onto money. The Siberian crane is portrayed on an old copper coin, proving the country has been the summer home to this migratory bird for more than a century.