Natures wonders: hummingbird collision avoidance (Introduction)

by David Turell , Friday, August 12, 2016, 21:39 (3023 days ago) @ David Turell

They use optical distance measures.-http://www.evolutionnews.org/2016/07/how_hummingbird103016.html-"Hummingbirds have a unique collision avoidance system built into their brains that allows them to perform high-speed aerobatics in safety.-"The super-agile birds, whose wings beat up to 70 times a second, can hover, fly backwards, and whizz through dense vegetation at more than 50 kilometres per hour.-"How they manage to avoid potentially fatal crashes has remained a mystery until now. Researchers in Canada conducted a series of experiments which showed that the birds process visual information differently from other animals.-***-"Instead, they appeared to rely on the size of objects to determine distance, steering away from the stripes as they grew larger.-"'When objects grow in size, it can indicate how much time there is until they collide even without knowing the actual size of the object," says Dakin. "Perhaps this strategy allows birds to more precisely avoid collisions over the very wide range of flight speeds they use."-***-"The secret became clear: expansion of an object in any part of the field of view was the bird's cue to respond. They would slow down or steer away from anything that grew in size vertically.-"Collectively, our findings suggest that birds control forward flight by monitoring changes in the vertical axis: specifically, the height of features and vertical pattern velocity. This finding is consistent with other laboratory studies showing that flying birds rapidly stabilize key features in their visual field. In nature, collisions may be avoided by monitoring changes in the apparent size of features, such as trees and branches, as well as changes in the vertical position of those features. Although our experiments focused on manipulating a limited number of cues, we do not suggest that these represent the only visual guidance strategies used by birds.-***-"Neurons that compute expansion have been identified in the nucleus rotundus of the pigeon brain, part of the tectofugal pathway.... These cues can inform an animal about the nearness in time of an impending collision, triggering an appropriately timed response without knowledge of the true size or distance of the approaching object. It was recently discovered that the zebra finch nucleus rotundus also contains cells that respond during simulated flight if an approaching feature is located at the point of expansion, suggesting that the tectofugal pathway may also be involved in flight control.-"Flight control. That's design. Understandably, the scientists did not speculate about how flight control systems might have evolved."-Comment: My first thought is that the birds learned this by trial and error and their brain plasticity accommodated the trials. But consider how fast they fly. Could this have developed while sustaining many crash landings? Doubtful. How about direct design?