Humans have long been fascinated with the annual comings and goings of birds. But their journeys can be tough and perilous. On World Migratory Bird Day we take a look at some of the dangers faced by birds on the move.
Each year migratory birds, big and small, fly thousands of kilometers in search of the best weather and habitats for breeding, raising their young and feeding. As soon as the winter chill arrives, they fly off to areas where conditions are more favorable. These journeys are astonishing not only in their scope - the tiny arctic tern, for instance, makes a pole to pole trip of 70,900 kilometers, annually - but also because a migratory bird's excellent navigation skills would rival a GPS. Still, migratory birds' journeys are becoming increasingly hazardous because of - you guessed it - the unholy trinity of climate change, habitat destruction and poaching.
Disappearing resting stops
A bar-tailed godwit in its breeding plumage
Imagine you had travelled hundreds of kilometers by foot along a route you had used many times before. You're thirsty, hungry and your feet are aching. Now imagine the hotel in the middle of nowhere - your usual place of rest on this journey - had disappeared. The next hotel is a long way off and you've run out of food and water. What would you do? This is what's happening to birds. Cities, farms and industry are swallowing up rest areas critical for the frequent flyers. For instance, 65 percent of the Yellow Sea mudflats in China, North and South Korea, have been lost since the 1950s. The mudflats are of great importance to birds migrating along the East Asian-Australasian Flyway and their disappearance is contributing to rapid declines in species such as the bar-tailed godwit.
And expanding deserts
In other places, such as northern Africa, desertification is causing problems. Overgrazing in the Sahel - a grassland region on the southern edges of the Sahara and a favorite dining spot of millions of birds crossing the immense desert - has caused plants to disappear. As result, the Sahara is spreading, making it more difficult for some birds, such as sand martins, to cross. Fewer sand martins are gracing European skies compared to 50 years ago.
Across the globe each year, migratory birds are hunted in their millions for a variety of reasons, including subsistence use, recreational activities and traditional practices. Nets are one of the main methods used to capture them. For instance, along the north coast of Africa, nets kill millions of birds every year. The Mediterranean is also one of the worst regions for migrating birds. Two million were killed in Cyprus in autumn 2015, according to conservation group Birdlife. Species such as blackcaps, are caught using nets, guns or sticks covered in adhesive lime, and served as a local delicacy.
Dying for a delicacy
Further afield in China, another songbird has become an increasingly fashionable dish that's also thought to be medically beneficial. The small yellow-breasted bunting was a frequent sight in the skies over northern Europe, where it summers, and over its winter quarters in southern China and India. However, since the 1980s their population has plummeted 90 percent as demand for the "delicacy" has risen in wealthier Chinese circles.
Migrating has become a high-stakes obstacle course for birds thanks to man's contributions to the landscape in the form of tall structures, according to the RSPB, a British bird protection group. Wind turbines, lighthouses and power lines pose a threat to migrating birds through collision or electrocution, as do flares on floating oil and gas platforms at sea. Birds fly toward the light and are killed in the flames. Then there are skyscrapers, television aerials and radio masts. "Migration routes took thousands of years to develop; evolution hasn't prepared birds to cope with these modern hazards," says the RSPB.
Climate change and migration patterns
In some cases, unseasonable weather causes migratory birds to change routes, shorten or cancel their journeys. For instance, small bird species that usually leave the colder climes of northern Europe in winter for Spain or Portugal might stay put. If the weather changes, they are not able to cope with low temperatures and won't survive. The premature onset of spring weather also means birds are arriving and breeding earlier. While warmer temperatures mean flowers bloom and insects hatch earlier too, the peak times are longer aligned, meaning birds sometimes do not find enough food for their newborns.