Hummingbirds are extraordinarily agile birds, capable of navigating through the most cluttered environments to reach the most challenging flowers and insects. However, the exact way they execute these maneuvers has been a longstanding mystery. Deciphering their flight dynamics, a recent study reveals that they actually employ two distinct flight techniques to pass through tiny openings up to half their wingspan.
Typically, most birds freely extend their wings in the air without encountering many obstacles. In contrast, those that feed on nectar, fruits, and seeds often need to traverse highly cluttered environments and negotiate tiny gaps. To achieve this, they fold their wings and bring them close to their bodies to gain space. However, hummingbirds, or “oiseaux-mouches,” have lost the ability to fold their wings at the wrists and elbows. Despite this, they exhibit remarkable flight dynamics, surpassing most larger birds in agility.
Hummingbirds can perform stationary and backward flights, as well as ultra-fast and nearly omnidirectional acrobatic maneuvers. To enable these various maneuvers, their wings must simultaneously provide the necessary force and speed, executing between 40 and 50 beats per second. Unlike insects, these birds significantly alter the kinematics of their wings and the aerodynamic force vector relative to their bodies to generate nearly omnidirectional linear and rotational accelerations. Under certain conditions, they can transition from stationary flight to a radically different body orientation in less than 0.2 seconds (equivalent to 5 or 6 wing beat cycles)!
On the other hand, the study’s lead author, Marc Badger from the University of California, Berkeley (UCB), notes that unless hummingbirds employ distinct strategies for navigating narrow openings, they may be unable to enter spaces narrower than their wingspan. Despite their inability to fold their wings at the elbows and wrists, these birds can maneuver through dense foliage and deeply curved corollas. The study, detailed in the Journal of Experimental Biology, aims to unravel how hummingbirds execute such complex maneuvers in the blink of an eye.
Crossing Openings Smaller Than Their Span
To observe the flight dynamics of Anna’s hummingbirds (Calypte anna), experts constructed a chamber of 16 square centimeters, divided in the middle by a partition. On each side of the chamber were artificial flowers that were alternately filled with a sugary solution. When the birds were on one side, the flower on the other side filled with a solution (and vice versa) to encourage them to shuttle between the two sides.
The partitions were regularly exchanged and featured either circular or oval openings for the birds to move from one side to the other. The diameters ranged from the wingspan of the birds (about 12 centimeters) to half of that length (6 centimeters). Each type of partition (7 in total) was presented 10 times to each hummingbird, resulting in 140 high-speed filmed trials for each. Simultaneously, a computer program tracked the position of each bird’s beak and wingtips as it approached and passed through the opening.
Researchers observed that the birds used two distinct techniques to traverse the partitions. The first involved approaching the opening, hovering in front for a few seconds—likely to assess the gap—then laterally crossing the opening, extending one wing forward and the other backward, forming a more or less cross-like shape with their bodies, all while continuing to beat their wings. After this, they pivoted forward and continued flying to reach the flower. The second strategy involved folding the wings backward to keep them along the body and crossing the partition beak-first, resembling a high-speed projectile. The birds momentarily suspended their flight and resumed wingbeats once safely past the obstacle.
Analyzing the two strategies, Badger and colleagues noted that birds opting for the first strategy (lateral flight) tended to fly more cautiously and slowly than those using the second (bullet-like crossing). However, as they became familiar with the openings, they appeared to gain confidence and started adopting the second strategy. Nevertheless, the latter was almost always used for the smaller openings, particularly the 6-centimeter one.
These results demonstrate that hummingbirds have developed flight strategies specifically adapted to confined spaces, capable of traversing openings significantly smaller than their wingspan. Additionally, distinct cautious and confident approaches were identified. However, approximately 8% of the birds collided with the walls while passing through the openings, with one experiencing a major collision. Nevertheless, they quickly recovered to retry and successfully execute the adapted maneuver.