While at a raptor speech a while back ago the naturalist mentioned that owls have offset ears. One ear is located higher in the skull than the other. This is supposed to help the owl detect the location of prey due to the tiny time difference in which the sound reaches each ear. After doing some more research online, it seems that the offset ears are primarily found in owls that are nocturnal hunters. Specifically, I have found that Barn Owls left ear is higher than the right.

Barn Owl (Tyto Alba)-www.robinsonlibrary.com

Barn Owl (Tyto Alba)-www.robinsonlibrary.com

Are the ear openings are always higher on the left for each species of owl that has asymmetrical ear openings? I would guess that they are predominately the same unless this characteristic had evolved in more than one instance. Any additional information would be appreciated.

  • $\begingroup$ Are you asking if the left is always higher? $\endgroup$ – JYelton Oct 25 '17 at 1:23
  • $\begingroup$ Yes, that is correct. Is the left always higher? $\endgroup$ – wanderweeer Oct 25 '17 at 1:26
  • $\begingroup$ Great question. I checked a few of my ornithology texts and they conflict. Cornell Handbook of Bird Biology (2nd ed) states the Boreal owl right external canal is higher than the left. Ornithology by Gill, 2nd ed, states that the barn owl left is higher than the right. $\endgroup$ – JYelton Oct 25 '17 at 1:37
  • $\begingroup$ @JYelton - Thanks for looking into this. I wonder if there is some confusion in the texts with point of view when it comes to right or left. I asked the naturalist that was giving the talk on raptors the same question and he wasn't sure either. $\endgroup$ – wanderweeer Oct 25 '17 at 9:46

This is a good question indeed. If owls with asymmetrical ear canal openings have different arrangements, it would suggest that the asymmetry has evolved more than once and arrived at different solutions.

The Cornell Handbook of Bird Biology (2nd ed.) states that the Boreal owl right ear is positioned higher than the left. Ornithology by Frank B. Gill (2nd ed.) states that the barn owl left ear is higher than the right. If both of these reports are accurate, then we have two species that differ.

The Wikipedia entry on Sound Localization in Owls (section 3) also suggests that the asymmetry of different owl species may be a product of convergent evolution:

For example, in barn owls (Tyto alba), the placement of the two ear flaps (operculi) lying directly in front of the ear canal opening is different for each ear. This asymmetry is such that the center of the left ear flap is slightly above a horizontal line passing through the eyes and directed downward, while the center of the right ear flap is slightly below the line and directed upward. In two other species of owls with asymmetrical ears, the saw-whet owl and the long-eared owl, the asymmetry is achieved by different means: in saw whets, the skull is asymmetrical; in the long-eared owl, the skin structures lying near the ear form asymmetrical entrances to the ear canals, which is achieved by a horizontal membrane. Thus, ear asymmetry seems to have evolved on at least three different occasions among owls.

(Emphasis added)

I presume the source of the Wikipedia information to be from Konishi, Masakazu and Susan F. Volman, 1994, though it is not cited in the relevant paragraph.

Perhaps some other ornithological journals will have more specific information, perhaps even allowing us to trace these separate evolved structures. It may even become a great thesis project!

  • $\begingroup$ I saw that reference in Wikipedia too. I'm glad you have a pretty good idea of the source of the information because it's hard not to be a little skeptical - especially if it's not cited. It would be interesting to see if other nocturnal raptors have similar asymmetrical ears too. $\endgroup$ – wanderweeer Oct 26 '17 at 11:09

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