In the blink of a human eye, a hummingbird can beat its wing dozens of time, dive out of sight and even catch flying insects in midair. How is it possible for these tiny creatures to keep track of the world moving around them?
Their brains may be set up differently to better accommodate visual information coming from all directions, according to new research—which could have implications for the development of precision-flying drones and robots. In the motion-detecting part of the hummingbird brain—which is significantly larger than in other avian species—the neurons appear to be “tuned” differently, says lead author Andrea Gaede, a neurobiology researcher at the University of British Columbia.
"They're processing visual motion in a different way than every other animal studied to date," says Gaede.
In all other birds, amphibians, reptiles and mammals tested, including other species of small birds, the neurons of this brain area, known as the "lentiformis mesencephalic," are tuned to detect motion coming from behind better than other types of motion. This makes sense for most animals, Gaede says—an animal that can better sense motion on the periphery of its vision would be able to flee from potential predators approaching from the back.
Not hummingbirds. Gaede and her team took six anesthetized Anna's hummingbirds (Calypte anna) and put them into a chamber where they could see dots moving on a screen in different directions. They then recorded the signals coming from their brains using electrodes implanted in them in response to the different types of motion, and compared them to tests done the same way on Zebra finches and pigeons.
The researchers overcame significant difficulties to be able to adapt brain recording techniques to the small size and delicacy of the hummingbirds, said University of Chile avian neurology researcher Gonzalo Marín, who was not involved in this study.
Unlike in the finches or pigeons, the neurons in the hummingbirds' motion-sensing brain area appear to be tuned to prefer motion from all different directions fairly equally, according to the study published today in the journal Current Biology.
Why would the tiny hummingbird do things so uniquely? Because they have to, according to Gaede.
"They have to be aware of their surroundings in a different way than other animals," Gaede says. Think about it: When you spend a lot of time hovering in front of small flowers to drink, you need to have precise control of their movements—all while beating your wings around 50 times per second. Other birds like falcons may move just as quickly while hunting, but they're usually moving through open air without any obstacles nearby. "They're often hovering at flowers in a cluttered environment [...] they don't want to get knocked away," she says.
Being able to sense motion equally in all directions could also give hummingbirds an advantage when they're flying at high speeds, evading predators and doing intense mating dives to impress females. It would, however, not give them the same advantage in seeing potential predators from behind that other animals have.
Gaede hopes next to study hummingbirds as they're in motion to see how their brains are processing information. "It might be an even more interesting picture," she says, though the small size and dynamism of the birds makes it still unclear how that will be done. Marín said that similar studies of hovering insects have found responses to visual stimulation that were not seen when doing tests while immobilized.
In humans, neurodegenerative disorders such as forms of palsy that impair a person's balance might be harming the human motion sensing brain area, Gaede says. More research into how these areas process motion in hummingbirds could lead to better understandings of how this area works in humans too, and how it could stop working and be fixed. Learning more about hummingbirds hover so well could also help another flying thing that needs to hover precisely, Gaede says: drones.
"This could provide information for determining new algorithms for visual guidance," Gaede says. Companies might be able to better program how the drones use their cameras to avoid obstacles while moving and hovering, for example. One day we might thank hummingbirds when we receive our Amazon packages by drone.