There are roughly 10,000 species of birds on Earth, and just under half of them are migratory. About 4,000 bird species migrate back and forth between their breeding and wintering grounds, and for two-thirds of them this means long-haul journeys of up to 20,000 kilometers (12,400 miles) each year.
The birds can rack up impressive air miles. The cuckoo travels for a striking eight months of the year, and swallows can cover up to 1,000 kilometers a day.
More and more migratory birds are becoming endangered
Migratory birds face many dangers during their flights over land and sea, but their deadliest enemy is man. Climate change and hunting are among the biggest risks. Of the birds breeding in Germany alone, 43%, including many migratory species, are listed as endangered by the International Union for Conservation of Nature.
By some estimates, collisions with glass panes are the leading human threat to birds after habitat loss. An estimated billion birds die this way each year in the US alone, as they get confused by reflections of sky and trees in windows. While weaker migratory birds can die on the journey from exhaustion, glass also kills stronger animals with better prospects for reproducing.
The good news is that these accidents can be easily prevented, for example by applying printed patterns to glass windows. Studies have shown that bird-of-prey silhouettes, on the other hand, are ineffective as deterrents.
A recent British study documented how birds are at particular risk from wind turbines located along migratory routes such as the German Baltic coast, the western Mediterranean coast of France and the southern coast of Spain. However, the study also shows that there are many locations for new wind turbines where the risk is significantly lower.
Power lines are more dangerous than wind turbines
There are other straightforward ways to prevent bird collisions with wind turbines, such as sensors that automatically shut them down when animals approach. And researchers from Norway found that if rotor blades are painted black, birds can better recognize and avoid them.
Significantly more birds die from power lines than from collisions with wind turbines, according to the study. Power lines pose a particular danger to animals that fly low to the ground. Again, the study found that marking power lines more conspicuous could help.
People also kill migratory birds intentionally. In the Mediterranean region alone, a good 20 million wild birds are illegally hunted or shot each year.
Illegal hunting of wild birds
Wild birds are considered a delicacy in many countries around the Mediterranean, including Egypt, Italy, Cyprus, France, Malta and Lebanon. Most are sold on the black market to restaurants or private individuals.
Caught in nets, with snap traps, or with glue applied to branches, the animals usually die in great pain. Glue-rod hunting is banned in the EU.
How climate change affects migratory birds
Climate change is now also influencing the behavior of migratory birds. Milder winters mean more and more birds are choosing to forgo their journey and stay in their breeding grounds all year round. This is mainly an issue for partial migrants: species such as robins, of which some individuals usually migrate and others do not.
Yet short- or medium-distance flyers, such as starlings, are increasingly staying in their summer territory all year round, too. The advantage is that those who stay in the breeding area during the winter can make an early start on grabbing the best nesting spots in spring, meaning those who do travel may miss out.
Climate change is also causing major problems for long-distance migratory birds. According to the British Royal Society for the Protection of Birds, more than 80% of Europe's long-distance avian travelers already have to fly longer and farther to find wintering grounds with enough food. Nightingales, researchers predict, will likely have to travel a good 800 kilometers farther in 2070 than they do now.
Instead of moving to Spain and North Africa, as they did until a few years ago, many blackcaps now migrate from Central Europe to Great Britain in winter. The increasingly mild climate there now makes wintering possible. Another clear advantage is that the flight distance is much shorter and there are no dangerous glue rods or trap nets.
This article was translated from German by Johanna Thompson.