Feb 24 2010

Why don’t they fly?

Published by at 7:12 am under Bird Behavior

Ostrich at Ngorongoro, photo by Wikimedia user Nicor
Huge flightless birds occur on many continents.  The ostrich lives in Africa, emus and cassowaries in Australia, rheas in South America and the giant moa, now extinct, in New Zealand.

For a long time scientists thought all these birds had a common flightless ancestor which lived on the mega-continent Gondwana before it separated into today's smaller continents.  The theory was that the flightless birds were stranded on their separate lands and then diverged.

But now, thanks to DNA sequencing of the giant moa, scientists at Australian National University (ANU) have shown that its nearest ancestor is a small flying bird, the tinamou of South America.  Long after Gondwana broke apart the tinamou flew to New Zealand.  Millions of years later some of its descendants had evolved into the giant moa.

Why did this happen?  The ability to fly is such a huge advantage, how could these birds afford to lose it?  ANU's molecular dating suggests that the flightless species had been flying birds who fed on the ground and could run well.  When the dinosaurs went extinct there was suddenly a lot of food, fewer predators and less need to fly to escape them.  Over time some ground-dwelling birds became quite big and heavy.  They didn't need to fly and eventually they couldn't.

Voila the ostrich!  An unexpected outcome from of the extinction of the dinosaurs.

For more information see this article in Science Daily.

(photo by Nicor from Wikimedia under Creative Commons Share Alike 3.0 license. Click on the image to see the original)

4 responses so far

4 Responses to “Why don’t they fly?”

  1. Carol kyrimeson 16 Feb 2017 at 7:33 am

    Another example of use it or lose it.

  2. Glendaon 16 Feb 2017 at 8:33 am

    Didn’t birds evolve from dinosaurs? If so, doesn’t it follow that all dinosaurs didn’t actually go extinct? And, could some large birds have evolved from the dinosaurs without going through a flying stage?

  3. Kate St. Johnon 16 Feb 2017 at 9:06 am

    Glenda, correct on many counts! Yes, birds are the descendants of theropod dinosaurs. The asteroid event killed the *large* dinos and left the small ones. In the absence of large predators including Tyrannosaurus Rex (who was himself a theropod) the next-to-largest birds no longer needed to fly … so they didn’t and now they can’t. So yes, some large bird ancestors (T.Rex) evolved without a flying stage … but they’re extinct.

  4. Glendaon 18 Feb 2017 at 9:11 pm

    Thanks! More reasons that birds are cool!

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