Wednesday, January 23, 2008

Because she wants to know

Recently, Lynne asked a desperate question and really, really wants to know...

Why are some owls' eyes yellow or orange, and others are brown?

That's a darn good question. A question that does not have a simple answer.

Bigger brains than mine have puzzled over this. But here is where my train of thought went:
Okay. North American owls have either yellow or brown eyes, and European owls have orange eyes. It's not a "light-gathering thing" with the yellow eyes, because if it was, all owls would have yellow eyes.
Let's think about our owls on this side of the pond...

Great horned owls: Yellow
Western and Eastern screech owls: Yellow
Maybe tufted owls have yellow eyes and non-tufted owls have brown eyes?

I AM happy

Two owls two ears

Elvis is not amused.  Ever.

Nope. Snowy owls are non-tufted, and have yellow eyes.

(This is Ghost, an education bird at Bird TLC, Anchorage Alaska)

And Northern saw-whets have yellow eyes, and no tufts.
And great gray owls...same thing.
Crap. What else?

Well, why do humans have green, brown or blue eyes? A species accumulates a trait through evolution because the environment has placed selective pressure on that species to survive with those traits.
Example: People whose descendants are from lands near the equator tend to have dark eyes, to help protect their eyes from the harsh sunlight. Same thing with darker skin and courser hair. And those whose descendants are from more northern climes are lighter skinned and have lighter eyes, because less protection was needed.

So, did dark-eyed owls evolve from earlier bird life that lived in the south? And lighter-eyed owls come from primitive Northern birds?
Let's list some "Northern" and "Southern" owls:
Great gray owl-Y
Great horned owl-Y
Snowy owl-Y
Northern hawk owl-Y
Northern saw-whet owl-Y
Boreal owl-Y
Short-eared owl-Y
Northern pygmy owl-Y
Flammulated owl (whose range is both northern and southern parts of the west-B

Whiskered screech owl-Y
Burrowing owl-Y
Central American pygmy owl-Y
Fulvous owl-B
Chaco owl-B
Spectacled owl-Y
Long-whiskered owlet- RED!
Striped owl-B
Mottled owl- B

So. While this is in no way a scientific study here, and there are like 175 owl species in the world and I just don't know them all...What I see from this very small amount of searching, is that a good number of Northern owls have yellow eyes, while Southern owls are sort of split.
So is this evidence for the argument that this is an evolutionary trait? Not really. But it begs the question, "Is there something to that?". Who wants to give me a grant so I can go travel the world and study this? This could go on and on...there are nearly 10,000 bird species in the world, and some of them have yellow, white or red eyes, and the rest have black or brown.
Interesting fact I came up with...Birds have 5 eye color variants, humans only have 3.

The short answer is, "No one is sure."

The really long answer is, "No one is sure, and definitely that Susan Gets Native person doesn't know. She isn't giving us anything Earth-shattering. Why do we come here? Man, I came here for funny videos. How about some shots of those cute dogs she has?"

I invite all to ponder this and comment. But no bashing my research skillz...I took Advil PM a while ago for a killer headache, so I be fuzzy....


Trixie said...

Fuzzy or not, you laid that argument out nicely. I have nothing to further this discussion. I do find it interesting, though. You is smart, Suzan!

Lynne said...

Yes, you IZ smart Susan! That's the best answer I've ever gotten to that question and I've asked it several times of different people. Thanks for researching it for me. Maybe you should start a new weekly blog column-
"Just Ask Susan"

Really. Thanks!

Susan Gets Native said...

Trix: Aw shucks. I promise not to let it go to my head.

Lynne: Anytime for you, dear Lynne.
I'm thinking of using a Q & A section for our RAPTOR newletter. This is a great question...that NO ONE can answer 100%
I like the idea of having a blog column...have folks send in questions? Might get hilarious. Especially if we don't stick to just birds.
Hugs (And thanks right back to know what I mean)

donaldthebirder said...

You are on the right track. I remember Gloger's rule (click to see an explanation) from biology. One owl I don't see on your list is the Barn Owl. I tend to think of the Barn owl as a southern owl. The Grass owls and Bay owls are southern owls derived from the same common ancestor as the barn owl and all have dark eyes.

Disclaimer: I am not a biologist, just have an AS in biology. Although I have held a volunteer position as a field biologist once, I am just a grocery store stocker ;-)

The Swami said...
This comment has been removed by the author.
The Swami said...

Dear Bird Answer Person,
You are, once again, overlooking the obvious.

The eye color is a result of the owls diet.
Most dogs have brown eyes.
The southern owl's diet would include hush puppies, and other dogs.
There, wasn't that simple?

No, no, really, it is not necessary to thank me

Owlman said...

I have a question for you at

I think the answer is pretty straight forward, although it would be awesome if it wasn't. My vote goes to pirate syndrome ;-)

Mary said...

Sounds good to me! You iz smart, Susan. If you offered a definitive answer, I'd just smile, nod and say, "and their eyes are so purdy, whatever the color. Oooo."

Richard said...

Best theory I've heard so far. Maybe it also has to do with longer nights in the winter up north or light off the snow. I came for another video of putting Priscella in the carrier. Wait...we never really saw Priscilla did we?

Grace, Every Day said...

Owls are pretty.

I am not a bird person, and simple biology makes sense to me. I agree with Swami's theory.

And thanks to you, Susan, I believe that owls are really, really beautiful.


Dave said...

That's one handsome snowy owl. :)