Every year, billions of small birds make one of nature’s most astonishing journeys, flying thousands of kilometres between Europe and sub-Saharan Africa and Asia, crossing scorching deserts and open seas with no place to stop, rest, or eat.
Now, a new international study published in the journal iScience has revealed a surprising secret behind how these tiny travellers survive.
The study has found that birds successfully undertake extremely long journeys by changing altitude while flying. They change the level at which they fly depending on what lies beneath them, with their body shape and feather colour also playing an unexpectedly bigger role.
HOW DO BIRDS FLY?
Using miniature multi-sensor tracking devices, researchers tracked 17 species of small migratory birds as they crossed two major barriers on their journey: the Sahara Desert and large marine areas such as the Mediterranean Sea and the Bay of Biscay.
The findings were quite revealing.
When crossing the Sahara Desert, birds typically fly at much higher altitudes than over the sea, often reaching 2,500 to 4,000 metres above sea level, especially during daytime.
In contrast, sea crossings usually occur at much lower altitudes, sometimes probably just a few dozen metres above the water surface.
Naturally, the next question was why.
The researchers behind the study found that the reason birds climb so high over the Sahara is due to the heat.
“These small birds fly almost exclusively at night, but they sometimes extend their night flights into the following day when crossing the desert. When the sun rises, we have found that they fly higher,” senior researcher Jocelyn Champagnon from Tour du Valat explained. “This behaviour probably helps them avoid overheating by reaching cooler air at higher altitudes. Conversely, when crossing the seas, they descend, which puts them at risk of colliding with future offshore wind developments.”
When it came to the role of a bird’s colour or its shape, the study became particularly fascinating.
Birds with larger wings tend to fly higher, likely because the larger wing area provides more lift in thinner air. Darker-plumaged species flew higher during daytime desert crossings, probably to reduce heat absorbed from solar radiation.
In other words, a bird’s feather colour is not just about appearance as it directly shapes its survival strategy across thousands of kilometres.
DOES THIS MATTER FOR BIRD CONSERVATION?
The findings will play a significant role in understanding birds and their behaviours, and thus, will inform the ongoing global efforts to protect endangered bird species.
Long distance migratory birds are declining. The findings, therefore, will also have implications for wind energy development in marine environments.
Many migratory birds cross seas at low altitudes, sometimes flying close to the water surface, which may bring them into the range of offshore wind turbines during long-distance flights.
Understanding when, where, and how high birds fly over marine areas can help improve the planning and operation of wind farms, reducing collision risks.
The study is a reminder of how finely tuned nature is, and how much we still have to learn before we build across its ancient flight paths.
Be it the popular Amur falcons flying from Asia to Africa, or other migratory birds like the Siberian Crane, the findings will help insulate their long journeys from human threats present at every corner.
