April 18, 2024

I, Science

The science magazine of Imperial College

by Ellen McNally (15 November 2023)

Hummingbirds are typically characterised by being agile, speedy birds reaching speeds of up to 30 miles per hour, but they have another skill to add to their roster. Researchers from University of California, Berkley have found that hummingbirds travel sideways through small gaps to reach their intended destination.

The discovery of this innovative method, not widely known due to hummingbirds manoeuvring too quickly for the human eye to see, was published on Thursday Nov. 9 in the Journal of Experimental Biology.

Many birds cruise through the air unhindered. However, species that feast on seeds, nectar and fruit for survival must navigate through tiny gaps in vegetation.

Typically, birds bend their wings to transport through, but hummingbirds are unable to bend their wing bones mid-flight. So how exactly do they negotiate these obstacles?

Hummingbirds employ two tactics. The most innovative of the two involves thrusting one wing forward while sweeping the second back, resulting in a sideways shuffle through the narrow gap, flapping their wings continuously to avoid losing height. On approach, the birds often hovered briefly to gauge the gap before passing through.

The senior author of the study Robert Dudley was stunned to see this, stating that “This concept of sideways motion with a total mix-up of the wing kinematics is quite amazing – it’s a novel and unexpected method of aperture transit.”

However, if the bird was more acquainted with the system, they resorted to the second method, which involved pinning their wings back towards their bodies, allowing them to shoot through like a bullet.

The results were recorded by using a two-sided flight arena. The team trained the birds to fly through a 16-square centimetre gap smaller than their wingspan, in the partition separating the two sides.

Flower-shaped feeders containing a sip of sugar solution were used on both sides, acting as a reward to encourage the bird to keep travelling back and forth.

The researchers then varied the shape and size of the aperture, filming the bird’s flight with high-speed cameras. The sideways shimmy was commonly used, however once the birds started approaching the smallest apertures, the birds automatically switched to the tuck and glide method, even though they were unfamiliar with the setup.

Marc Badger, first author of the study declared that “Learning more about how animals negotiate obstacles and other ‘building-blocks’ of the environment, such as wind gusts or turbulent regions, can improve our overall understanding of animal locomotion in complex environments.”

Dudley and his team hope to conduct further experiments in the future with a series of different apertures to determine how birds manoeuvre numerous obstacles.