Hummingbirds navigate narrow spaces with their remarkable flight abilities

Hummingbirds are renowned for their ability to perform aerial acrobatics, demonstrating unique flight patterns that allow them to fly upside down and backwards. A recent study using high-speed video has revealed a new dimension to their flight skillset, showing that hummingbirds are capable of passing through gaps narrower than their wingspan, using certain aerial maneuvers.

Unlike other birds that can bend their wings at the wrist to move through dense vegetation, hummingbirds demonstrate less flexibility in the movement of their wings. To navigate through narrow spaces, hummingbirds, due to their wings sticking out directly from their bodies, resort to some intricate maneuvering.

A recent study, published on November 9 in the Journal of Experimental Biology, has shown that Anna’s hummingbirds (Calypte anna) fly sideways to move through spaces that are too small for their inflexible wings. To prevent clipping the sides of a hole they traverse through, the birds flutter their wings while maintaining their path through confined spaces, rather than employing their full wingbeat range. After a few successful attempts through an obstacle, the birds alter their strategy to flatten their wings against their bodies and dart through the openings in the manner of a bullet.

“This revelation offers a new view into the phenomenal capabilities of hummingbirds,” says Bret Tobalske, a biomechanist at the University of Montana in Missoula who was not involved in this study. He finds its findings highlighting the unique sideways flight maneuver to be “quite extraordinary,” demonstrating once more how special hummingbirds are among avian varieties.

This research could aid engineers in designing drones or robots capable of navigating intricately tight spaces. Noted for their flight control prowess and excellent spatial memory, hummingbirds offer engineers a wealth of inspiration. However, as pointed out by Bo Cheng, a mechanical engineer at Penn State not involved in the study, drone technology has not yet reached the flight competency seen in hummingbirds. The high-speed beat of a hummingbird’s wings - approximately 40 beats per second for an Anna’s hummingbird - affords them precise control during flight, an ability that engineering is still trying to replicate.

The rigidness of hummingbird wings prompted biologist Marc Badger to question just how these little birds cope with obstacles and confined spaces. While a doctoral student at the University of California, Berkeley, he observed the swift birds consuming nectar from feeders and occasionally chasing one another through nearby bush branches with no visible injuries. This observation led him to question the secret behind this skill.

Throughout his research, Badger and his team captured four male Anna’s hummingbirds in the wild and acclimatized them to fly between two feeders inside an enclosed flight area. The team introduced obstacles with an opening ranging from 6 to 12 centimeters in diameter, equivalent to about a half or a full wingspan of a hummingbird, once the birds became accustomed to the new environment.

To the naked eye, the hummingbirds moving between feeders might seem like blurry figures on a computer screen tracking the area, according to Badger, who presently works as an engineer at Aescape, a therapeutic robotics firm based in New York City. However, high-speed cameras positioned on the side and beneath the hole revealed that the birds, initially, used a sideways flight technique to navigate through constricted spaces, eventually switching to diving through the hole.

“The sideways scooch was a startling revelation,” remarked Robert Dudley, a physiologist at UC Berkeley. He had assumed hummingbirds would resort to the ballistic strategy, pulling their wings against their bodies, as most songbirds do. “To see that they slow their speed and then maintain their altitude while moving sideways was an unexpected behavior which had never been seen before,” he added.

Whether these navigation techniques were learned during the course of the study or whether the hummingbirds used inherent strategies remains unknown, says Badger. He observed that all four birds began with the sideways flight technique before transitioning to the bulletlike method suggesting that these tactics are likely also used in the wild.

The exact reasons why hummingbirds might employ either technique is another area needing further exploration. According to Badger, the sideways flight technique could potentially provide flexibility to steer clear of predators hiding behind obstacles. There is, however, a downside, as continuous wing flapping may cause the feathers to hit objects and possibly shatter. “My theory,” says Badger, “is that they picture what lies ahead and understand their environment first, at which point they switch to the more ballistic method to avoid potential hazards.”

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