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Bio-bullets

Why external ears are redundant in birds

No bird uses external pinnae to sense the direction of sound. This is because birds have effectively turned the mammalian ear outside-in.

professor caricatureProf. Mumblebard claims: "Because birds typically need to be streamlined to fly, they have minimised the external ear and instead compensated by seeing better than most mammals do. Flightless birds no longer need streamlining, but the flying ancestors of ostriches, kiwi and their relatives happen not to have possessed the fleshy pre-aural flaps seen in certain owls. The tinkering of{njaccess 2, 3, 4, 5, 6, 7, 8} natural selection cannot be expected to reinvent such structures." {!njaccess}… See the hidden half of Prof. Mumblebard’s claim by subscribing here{/njaccess}

logoRobin and the Honey Badger respond: "There must be a more basic reason why all birds lack external ears despite possessing suitable anatomical structures such as stiff plumage, wattles or foldable tufts of long feathers close to their ear apertures. The middle ear is consistent across{njaccess 2, 3, 4, 5, 6, 7, 8} all birds in having extremely complex sound-vibrating surfaces which are – in contrast to the middle ear of mammals – not partitioned between left and right. Furthermore, the mammalian eardrum transmits sound waves only from outside to inside, i.e. from air to bone. By contrast, the avian skull is designed to transmit sound from one ear across to the other by means of internal air passages in the cranium; and membrane-like skull bones of birds, surrounded by air inside the skull, act as extensions of the eardrums. Because pressure-waves can reverberate through the gas in the cranium, birds can sense the direction of sound as efficiently as in mammals while retaining a light, manoeuverable head."{!njaccess}… Reveal the hidden half of this response by Robin and the Honey Badger by subscribing here{/njaccess}

 

Please join us here at the Bio-edge with your own comments. In the discussion below we encourage links to any evidence supporting either Prof. Mumblebard or Robin and the Honey Badger. Illustrations are welcome but please cite all sources or we may be forced under copyright to delete your comment.

 

Why external ears are redundant in birds

Last modified on 13 July 2015

Comments   

0 #1 Biodiver 2014-02-10 12:49
The King of Saxony bird of paradise sure shows that birds could have evolved ear-like appendages if they needed them:

0 #2 Sanders 2014-02-11 11:53
I’ve often wondered why eared owls don’t use their ears to hear and why some owls have ears and others don’t.
0 #3 Ornithophile 2014-02-13 16:15
Owls may not have ear pinnae but their outer ears can be a lot more complex than the outer ears of mammals, as seems obvious from this photo.


attributed smartneddy, taken in Chang dao Bird Band Center, China
0 #4 Sanders 2014-02-14 14:27
Tell me please Ornithophile, which species of owl does your photo belong to and does it have feathered ‘ears’?
0 #5 Ornithophile 2014-02-14 14:30
@ Sanders: It’s not my photo but it’s the long-eared owl, Asio otus. Yes, this species has long ear-tufts. That’s what’s strange, its got these long feathers that look like external ears and meanwhile it uses this complex ear opening instead.
0 #6 Redfern 2014-02-14 14:31
www.youtube.com/.../ shows how sound waves penetrate a human skullbone. Has anyone seen a clip showing how they go through a bird’s skull, which of course is more flimsy?
0 #7 Zoophile 2014-03-06 14:00
You don’t have to go any further than the domestic chicken to see that birds can have wattles on their heads that are as big and complicated as most external ears in mammals. It does seem a bit crazy that fowl and pheasants go to all the trouble of growing these fleshy outgrowths and then don’t bother to use any of them to help their hearing.
0 #8 Biodiver 2014-03-06 16:43
@Ornithophile



says that owls don’t really have feathers acting as ears. But everyone knows they have asymmetrical ear holes which helps them find prey in the dark – ears at different heights can pinpoint the sound waves...Maybe also compensates some for not having real external ears?

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