Birds have always been a source of inspiration for humanity, with airplanes suggesting a human desire to imitate them. But they have more to teach than the power of flight. Twice a year, when hibernating animals like bears and squirrels are either curling up for a deep sleep or stretching their way into spring, migratory birds are getting ready to embark on epic journeys over land and sea.

And in so doing, they play a crucial role in keeping nature in balance. As they fly from one place to another, pollinating plants, spreading seeds and controlling pests by eating insects and other invertebrates, they help to maintain ecosystem health, which in turn contributes to food security. 

And that's not all. Francisco Rilla, a wildlife biologist and consultant to the UN focusing on conservation and migrating species, said migratory birds also serve as "bioindicators." 

In other words, because they tend to avoid polluted areas, their movements provide useful information in the assessment of water and air quality.

To the ends of the Earth and back 

On their fall journey, birds watch the waning daylight — which they understand to mean essential food will soon be in shorter supply — for a sign that it's time to head south.

Some, like the tiny Arctic tern, leave the dark cold Arctic for the winter, flying all the way to the Antarctic Circle, clocking up a round trip of some 90,000 kilometers (55,900 miles). This extensive journey makes them the world-record holders for the longest migration route in the animal kingdom.

Another champion is the bar-tailed godwit, which flies from the northern US state of Alaska to the Australian island of Tasmania. A 5-month-old bird holds the Guinness record for the longest nonstop flight, having covered 13,560 kilometers in 11 days and one hour. 

Bar-tailed godwits, which feed for two months in Alaska, can shrink the size of their internal organs to create space for the energy-rich fat stores needed to keep them going during the long journey. But for some species, climate change is making such a feat less likely.

How is human activity affecting migration?

Migrating birds use the sun, stars, coastlines and large bodies of water to guide them on their journeys across the world. But some places where they stop to rest and refuel along the coasts are being altered by floods connected to rising sea levels.

Small crustaceans, which are an important food source for migratory birds, can struggle to build their shells and skeletons in oceans made more acidic by having to absorb more carbon dioxide. And this has a knock-on effect on migratory birds.

Without sufficient food, they are less likely to survive arduous journeys or successfully reproduce.

Birds, like humans, are also threatened by the increasing intensity and frequency of extreme weather events such as storms. Strong winds can drag them down and kill them.

Equally, climate change can impact how migratory birds behave.

Warmer temperatures can remove the threat of food scarcity, leading birds to shorten their routes or not flying back to their original habitat at all.

This, in turn, can lead to conflicts over food between migratory birds and resident animals. While some migratory birds, such as the Arctic tern, have compensated for strong winds by expending more energy on their journeys, other species have succumbed to the pressures of human activity.

One such bird was the slender-billed curlew, which was declared extinct in 2024. Researchers believe the breed failed to adapt to habitat loss.

How to help migratory birds on their journeys

Though humans often feed birds, Rilla said putting food out for migratory birds can do them more harm than good. If they are given bread and seeds meant for people, they might feel too full to eat the things that provide them with crucial nutrients. He added that putting food in places where it will be easy to spot could expose birds to predators.

Instead, Rilla recommended helping these travelers by urging governments to expand the network of protected areas through international treaties such as the Convention on the Conservation of Migratory Species of Wild Animals.

The United Nations Environment Program is aligned with these recommendations, but suggests going further by creating more bird-friendly places. This year's World Migratory Bird Day, on May 10, emphasizes promoting the coexistence between humans and birds. The key message is encouraging the creation of healthy habitats, reducing pollution and avoiding glass buildings, which pose a significant collision risk for birds.

If migratory birds start to disappear, it could affect agriculture and the food chain. In other words, as Rillo said, "whatever happens to them could also happen to us."

Edited by: Tamsin Walker