Hummingbirds: reversing is not a flight played backwards

A hummingbird can approach a flower, hover and then back away without turning around. In Anna’s hummingbird, Calypte anna, Nir Sapir and Robert Dudley studied this manoeuvre experimentally. Their 2012 paper is not a new report from today: we revisit it to understand the precise coordination hidden within an apparently simple scene. The species, also described by the Cornell Lab, occurs along North America’s Pacific coast and is known for its particularly brilliant plumage. [1][2]

The researchers observed five males in a wind tunnel, comparing backward flight, forward flight and hovering. To make the trials comparable, the birds fed at a device while airflow changed in relation to their position. High-speed recordings described the movements, while oxygen consumption allowed the team to assess metabolic cost. Watching a video and deciding which movement looked more tiring would therefore not have answered the same question. Appearance and measurement do different jobs. [1]

In backward flight, the body became more upright, the head bent further and the plane of the wingbeat moved closer to horizontal. This is a different coordination of parts, rather than the same action played backwards. Kathryn Knight’s account for the Journal of Experimental Biology connects these details with the natural scene: after reaching nectar, a hummingbird must be able to withdraw from a flower without making a large turn to face the opposite direction. [1][3]

At an airspeed of 3 metres per second, oxygen consumption during backward flight did not differ significantly from forward flight and was about 20% lower than during hovering. The result belongs to these trials, this species and this comparison. It does not mean that every backward manoeuvre by every bird always costs less. A wider range of speeds was studied in just one individual: an important limit when interpreting the finer details of the findings. [1]

Try an editorial observation exercise without disturbing animals: when watching a scientific video, pause to look first at the body and then at the wings. Does the bill point in the direction the animal is moving? Does the body keep the same angle? Writing down two separate observations helps distinguish orientation from direction of travel. It is a way to ask questions about footage; it neither recreates a wind tunnel nor measures energy use or speed by itself. [3]

The most useful discovery is therefore a small correction to how we look. An animal moving backwards need not turn around, nor simply reverse a familiar sequence of movements. The authors also note that backward flight is known in other groups of birds and insects, so we should avoid the absolute claim that only hummingbirds can do it. Their skill remains remarkable even when we give up the most convenient superlative in the story. [1]