Hummingbirds are the only birds that truly hover, in part due to their ultimate bird brains. Ruby-throated Hummingbird photo by Jim Konrad.

Hummingbirds are unique in many ways. Some of the smallest birds in the world, they are the fastest fliers relative to their body length, and they are also the only birds that can truly hover. To fly in this specialized way, hummingbirds have evolved several distinct adaptations, from a specialized wing shape to breast muscles that take up about 30 percent of their total body weight (most birds’ breasts weigh about 15 to18 percent of their total weight). Scientists have always suspected that the complex movement of hovering also requires a more complex brain, but hummingbird brains are very small and very hard to study.

Only recently did a team of Canadian scientists describe how hummingbird brains manage hovering. Their research, published in this month’s edition of Current Biology, shows that hummingbirds have brains unlike any other bird (or four-limbed vertebrate, for that matter), which permit them manage multi-directional flight.

According to the new research, hummingbirds spend a lot of their time hovering, which means they have more to consider than just front back-to-front axis flight. When hovering, a gust of wind might push them from the side, or a potential predator might strike from below. So hummers must be able to move in all directions.

The research team discovered that in an area of the brain called the lentiformis mesencephalic, which is the portion of the brain that responds to visual stimuli, hummingbirds didn’t have a strong back-to-front movement preference like all other animals tested to date. Instead, they seemed to have no preference, responding to motion in every direction equally.

The researchers also found that hummingbird brains are tuned to respond more strongly to fast movements than slow motions. This was a surprise because scientists had assumed that hummingbird brains would be tuned for low-speed hovering. But if you think about it, being optimized for high speed makes sense, too: An Anna’s Hummingbird can move at 385 body lengths per second during mating flights, which is screaming fast. (By comparison, an F15 Eagle fighter jet has a top speed of Mach 2.5, which translates to about 45 body lengths per second.) At that speed, the ability to make nearly instant course corrections is the difference between life and death – or mating and not mating, which is basically the same thing in evolutionary terms.

The fact that hummingbird brains perceive the world differently than other vertebrate animals is a fascinating ornithological find, but the researchers have other motivations for their study – understanding flight in nature to design better robots. The discovery of an animal brain that can move efficiently in three dimensions could be very valuable for artificial intelligence in flying drones, for instance, or computerized autopilot systems for helicopters. But potential commercial applications aside, isn’t it interesting to think that the tiniest bird brains might also be the most complicated?

You can refer to the new scientific publication from Current Biology at https://www.cell.com/current-biology/fulltext/S0960-9822(16)31394-X

For the original article, see https://www.audubon.org/news/new-research-shows-hummingbirds-need-exceptional-brains-hover