March 18, 2015 | David F. Coppedge

Why Birds Don't Crash

A bird flying through a forest or city needs the reactions of a champion video gamer.  It’s got the software to do it.

Bob Yirka writes in PhysOrg about a new study that “shows one reason why pigeons so rarely crash.” The study, published in PNAS by Harvard researchers, finds that “Pigeons trade efficiency for stability in response to level of challenge during confined flight.”

Video gamers need fast reactions, but they don’t break bones or draw blood if they crash; birds can. You’ll respect avian aviation skills after reading the introduction:

The real world is a cluttered environment and animals traversing it are faced with innumerable obstacles in their normal locomotion. During normal flight, birds have to avoid hitting trees, lampposts, and other members of flocks. To investigate flight strategies used in these circumstances, we presented pigeons with a simplified challenge, a series of vertical gaps with variable spacings. The pigeons used two discrete postures. One posture granted them greater flight efficiency but was more disrupted when they collided with obstacles, and was used for traversing larger gaps. An alternate flight posture was less efficient but more stable when slight collisions occurred, and was used for traversing smaller gaps. To our knowledge, this is the first time we have seen flight strategies tuned during use in cluttered environments.

PhysOrg notes that pigeons “are some of the best flyers around” – better at avoiding obstacles than robins and other birds. The article explains how the birds moved their wings in a “deliberate act” to alter the strategy, depending on the spacing of the obstacles:

Amazing FactsTo pass between the pipes, the birds had to scrunch themselves a bit, but how they did so, the researchers found, depended on how far apart the pipes were. They noted that when the pipes were at least a half a wing length apart, the birds lifted their wings as if to flap as they approached the obstacle, but then held them steady, above their heads as they passed between the pipes, then flapped down as soon as they were through—a technique that led to very little loss of altitude, which meant it was quite efficient. But if the pipes were moved closer together, they pulled their wings into their body, a less efficient approach, but one much less likely to result in wing damage.

These champion flyers, though common on city streets, deserve our respect; “the birds somehow made a choice of which technique to use, just before they passed through—very impressive, especially when noting that birds, except for some such as crows or magpies, are not generally known for their smarts.”  Illustra Media knew something of their smarts. They called their documentary Flight: The Genius of Birds.

Other Bird News

Owl migration: Snowy owls are not famous as migrators, but they do migrate. Some secrets of their migration came to light in New York recently. On Live Science, Shannon Hall says they migrate between the Great Lakes and Florida. They were seen recently in wide-open areas, contrary to expectations, feeding on fish instead of lemmings, their presumed primary diet. We think of birds heading south for the winter, but not snowy owls! Scientists were shocked to see them out on frozen lakes, looking for fish, ignoring salt marshes full of rodents.  Hall found a way to insert “climate change” into the report.

Not extinct:  Happily, a bird thought extinct (last seen in 1941) has been rediscovered. Science Daily shares the good news that Jerdon’s babbler, a bird-in-the-hand size critter, was found in Myanmar.

Tree change-up:  It’s not uncommon to see “rethink” and “evolution” in the same headline. Another appeared on PhysOrg: “Researchers rethink how our feathered friends evolved.” One of the largest phylogenetic studies ever, involving “more than 200 researchers at 80 institutions in 20 countries, with related studies involving scientists at more than 140 institutions worldwide,” decided that the bird tree needs redrawing. That should come as no surprise, considering that there are plenty to choose from:

“For 50 species, more than 10 to the power of 76 possible trees of life exist. Of these, the right one has to be found,” said Andre J. Aberer, with the Heidelberg Institute for Theoretical Studies (HITS), in a news release at the time of the study’s publication in Science. “For comparison: About 10 to the power of 78 atoms exist in the universe.

So after crunching the data with supercomputers, using various algorithms like “Exascale Maximum Likelihood,” how do they know the “right one” has been found? They didn’t say. They mainly bragged about the equipment and computer hours logged. “Resolving the timing and phylogenetic relationships of birds is important not only for comparative genomics, but can also inform about human traits and diseases, according to the researchers,” the article ends, scrambling for practical applications. “For example, the study included vocal-learning species – such as parrots and hummingbirds – which can serve as models for spoken language in humans and may prove useful for insights into speech disorders.” Birds are pretty distant on the phylogenetic tree from humans.  It’s hard to see how “Polly wanna cracker” or “Hummmmm” will help a human patient needing speech therapy.

If you enjoyed Illustra’s film on avian flight, you’ll love the next one on marine biology. Release is scheduled for summer on DVD and Blu-ray.


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