World Migratory Bird Day: Flying for survival

Habitat loss is by far the biggest threat facing birds. Intensive farming and deforestation are making it harder for long-distance fliers to find the shelter and food they need to build strength for their taxing migration. Take the golden-winged warbler. Its numbers have dropped 60% in 50 years, partly due to land clearing for palm oil, coffee and cattle in its wintering grounds in South America.

Migratory birds also rely on key stopover sites where they can refuel — without them, species may never reach their destination and could eventually die out. The Yellow Sea wetlands shared by China and the Korean Peninsula are one of the most important rest stops for birds, but coastal development, reclamation for agricultural land and pollution have caused a decline in populations.

The critically endangered spoon-billed sandpiper is one of the species that relies on China's Yellow Sea coastline during its marathon journey from Russia to southeast Asia. There are only an estimated 210 pairs of the species left. In 2019, parts of the wetlands were added to the World Heritage List in an effort to prevent the sandpiper, and other endangered birds, from dying out.

Malta is another such stepping stone for more than 150 bird species traveling between Europe and Africa. The Mediterranean country is also popular with poachers, who kill or capture thousands of wild birds during spring and autumn hunts. The practice has been devastating for breeding populations of songbirds, especially finches. Sometimes a caged decoy bird is used to lure others within range.

Migratory birds also have to contend with man-made structures along their flying pathways. Collisions with wind turbines, skyscrapers and power lines are not uncommon. During the day, birds might be confused by the sky reflected in a building's window and plow into the glass. At night, they can be drawn to bright city lights or lighthouses, often resulting in fatal crashes.

Pollution that ends up in bird habitats inevitably impacts their food supply and health. If they ingest toxins or get oil on their feathers during migration, they may struggle to fly and may not survive the journey. Plastic waste in the environment is also a hazard, because it can look a bit like food to birds. If they eat it, it fills their stomachs and causes them to starve.

Changes in the climate are adding to stresses on bird habitats, prompting shifts in breeding and migration patterns. In the Sahel region of western Africa, prolonged drought has led to desertification, reducing green areas that migrating birds, such as these sand martins, rely on when crossing the desert on their long haul flights to Europe.

Studies show that rising temperatures are driving some species to take flight earlier, change their migration route, or cancel their journey altogether. Warmer spring weather also means flowers bloom and insect numbers spike earlier — that's bad news for long-distance travelers who might miss the peak abundance of their food sources, and won't have enough to feed their chicks.