2023-11-19 06:00:24
A Delphine’s Hummingbird or Brown Violetear (“Colibri delphinae”), in the cloud forest of San Antonio, near Cali (Colombia), February 23, 2018. LUIS ROBAYO/AFP
Not everyone is lucky enough to have hummingbirds in their garden. But even if you and I had, we are not sure that we would have found there material for scientific discovery. Marc Badger is a biologist at the University of Berkeley. Since his thesis, these champions of flight agility that are hummingbirds have occupied a large part of his research. And it was while observing their territorial disputes around the feeder that a question suddenly struck him. “I saw the dominant chasing the intruders and the latter fleeing through vegetation that seemed very dense to me. How did they get through? » In an article published on November 9 in the Journal of Experimental Biologyhe and his collaborators deliver a truly striking response.
The solution may seem obvious. To pass through openings smaller than its wingspan, a bird only needs to fold its wings. Except the hummingbird can’t do it. He who displays at the base of his wings the fastest active joint of the entire vertebrate world, who has developed unique aerial skills allowing him in particular to achieve his famous hovering, has paid the price for this power: an absence of intermediate joints. Shoulders, then, but no elbows or wrists. So how to do it?
To see this clearly, the researchers placed Anna’s hummingbirds – each wing of which measures 12 centimeters – in an aviary equipped with a central dividing wall. Using drops of nectar, they motivated them to cross the wall. Then they reduced the size of the holes: 12 × 12 cm, 12 × 8 cm, 12 × 6 cm, 8 × 8 cm, 8 × 6 cm and 6 × 6 cm. All under the eye of cutting-edge cameras, the sequences of which they slowed down and analyzed.
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To their great surprise, they saw two strategies emerging. In the first, the birds approach the hole cautiously then cross it sideways, one wing after the other, continually continuing their beats. The point-to-point analysis showed that if the second wing is always directed towards the rear of the body, the first takes different positions, towards the front or towards the rear. And, at any moment, the bird can turn back.
The second strategy is more radical: the hummingbirds rush forward, ball in head, interrupt their beats, stick their wings along their body… and pass. They only begin to wave their limbs again once they have passed the bottleneck.
Why two techniques? “Because it allows them to arbitrate between the different risks, depending on the situationexplains Marc Badger. If a predator, such as a cat, is on the other side, rushing through the hole is obviously dangerous. It is then better to choose the prudent strategy. But conversely, this poses a greater risk of collision of the wings against the wall and wear. So when the terrain is safe, they prefer freewheeling. Furthermore, this last strategy is the only possible one when the hole is really too small. »
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