Hawks fly in zigzag patterns to take advantage of strong tailwinds, study finds

The mystery of why Eleonora’s hawks migrate on longer routes in a complex ‘zig-zag’ pattern has long baffled scientists.

But they are now on the verge of discovering the answer after discovering that the birds do this not only to benefit from stronger tailwinds, but also to take detours to feed and avoid the entanglement of tropical rainforests.

This is because heat and rain can impact gliding and flapping when hawks fly overhead.

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The researchers wanted to know why the birds do not take the shortest route to reach their winter homes in Madagascar from their breeding grounds in the Canary Islands, as well as vice versa.

If the hawks were flying straight, they would have to fly about 4,900 miles (8,000 km).

However, the study by the University of Amsterdam and the Doñana Biological Station in Spain found that the birds actually traveled over 5,500 miles (9,000 km) on average in the fall and over 6,800 miles (11,000 km) in the spring.

They also spend six days more on stopovers in the spring than in the fall.

The study combined data from GPS trackers fitted to the falcons with global weather models and satellite imagery to uncover how seasonal winds and Africa’s diverse landscapes shape the migration of Eleonora’s falcons.

“It is striking that the number of flying hours flown in spring and autumn are the same, even though the spring routes are considerably longer,” said lead author Wouter Vansteelant, of the University of Amsterdam.

“There was a simple explanation for this when we linked it to the wind data: birds benefit from a stronger tailwind in the spring.”

To see how zigzagging behavior helped hawks maximize tailwinds in different landscapes, Vansteelant and his colleagues compared birds’ tailwinds at various points along the route of their chosen migratory path with tailwinds. they could have received over the shortest possible route. .

“The falcons turned out to zigzag in spring and autumn to get as much tailwind as possible – or as little headwind as possible – during the terrifying crossings of the Sahara Desert and the Indian Ocean,” said said Vansteelant.

“It’s a common and well-known strategy among migrating birds.”

If the hawks were flying straight, they would have to fly about 4,900 miles (8,000 km). However, the birds actually travel 5,500 miles on average in the fall and 6,800 miles in the spring.

The researchers also found that the falcons made direct flights east or west over the Sahelo-Sudanese zone in both seasons, giving them less tailwind than they could have given them. find on a shorter route.

However, the wind is relatively light in this region, and these east or west detours have allowed the falcons to drastically reduce the flight distance over the rainforest of the Congo Basin in the fall and over the Sahara. in spring.

Complex: The mystery of why Eleonora’s hawks migrate on longer “zig-zag” routes has long baffled scientists. They fitted the birds with GPS trackers (pictured) in a bid to learn more about their behavior

Indeed, the heat can hamper the birds’ flight abilities, while the rain over the Congo Basin impacts their restless flight, the researchers said.

“Birds migrate via detours more frequently than they follow direct routes,” Vansteelant said.

“It is likely that many other migratory bird species react to wind conditions in an equally flexible way.

“When faced with strong headwinds, birds are better off flying away from the shortest route until they can get back on track through weaker or higher wind fields. favorable.

“When the wind is weak or favorable, on the other hand, birds may also take detours for other reasons, such as rounding barriers or going to quality foraging areas.”

Despite the discovery, the question remains how the falcons manage to find and navigate these complex routes.

Vansteelant said: “We have now been able to track a number of hawks for four consecutive years.

“Based on this data, we will be able to determine how consistent they are in their route choices and timing, and how much they improve their migration performance through experience.”

The study was published in the journal Ecology of movement.

WHY DO MIGRATORY BIRDS FLY IN A V FORMATION?

Birds fly in a V formation to help them fly more efficiently, staying aloft while expending as little energy as possible.

Scientists learned the secrets of migratory bird aviation after attaching tiny recording devices to a flock of 14 northern bald ibises that not only tracked their position and speed via satellite, but measured every wing beat .

The 14 birds used in the study were hand-bred at Vienna Zoo in Austria by the Waldrappteam, an Austrian conservation group that reintroduces northern bald ibs to Europe.

Birds fly in a V-formation to help them fly more efficiently, staying aloft while expending as little energy as possible (stock image)

The birds were studied as they flew alongside a microlight on their migration route from Austria to their winter home in Tuscany, Italy.

Lead researcher Dr Steve Portugal, from the Royal Veterinary College, University of London, said: ‘The distinctive V-shape formation of flocks of birds has long intrigued researchers and continues to attract scientific and popular attention. , but a definitive account of the aerodynamic implications of these formations has remained elusive until now.

“The complex mechanisms involved in V-formation flight indicate a remarkable awareness and ability of birds to react to the wing trajectory of nearby flockmates. V-formation birds appear to have evolved complex phasing strategies to cope with the dynamic wakes produced by wing flapping.

When flying in a V-formation, the birds’ wing flaps were approximately “in phase,” meaning all wingtips followed roughly the same path, the scientists found.

This helped each bird pick up additional lift from the upwind of its neighbor ahead.

Occasional changes in position within the formation meant that sometimes the birds flew directly behind each other.

When this happened, the birds changed their wing beats to an out-of-phase pattern to avoid being caught in the wind.