Nearly eleven years after I took the photo I think I finally solved the mystery. Maybe. Sort of.
This image of three young sibling Burrowing Owls warming up in the morning sun on Antelope Island is among less than a handful of my favorite Burrowing Owl photos, even though the youngster on the left isn’t quite as sharp as the other two. I was just lucky to get three of them in my viewfinder at the same time with all three well separated from each other in beautiful warm light.
- I’m about to go down a long and convoluted rabbit hole that I suspect at least some readers will wish they hadn’t followed. It’s your choice.
The photo was taken on August 17, 2010 and the first time I looked at it I was struck by the huge disparity in pupil size between the bird in the middle and the two others. All three birds are looking in the same direction (at me) but the pupil of the middle bird appears to be about 5-6 times smaller than the pupils of the other two. I posted the photo to Feathered Photography back in 2013 but I forgot to mention the unusual disparity in pupil size in my text and few if any readers noticed it back then so until yesterday I hadn’t thought about it in all those years.
But last night I noticed two things that had escaped me earlier. Even though all three owls are looking at me their heads aren’t all facing quite the same direction. The bird in the middle is facing me directly but the other two appear to be facing (not looking) slightly over my left shoulder. And then I noticed that the catch light on the middle bird is almost dead center on its smaller pupil while the catch lights of the other two birds are significantly to the right of center on their much larger pupils.
The position of the catch lights of all three birds “matches” the direction they were facing relative to the sun. To me that suggests that as a result of their relative head angles more light was reaching the retina of the middle bird resulting in a smaller pupil. The dramatic difference in pupil size seems surprising to me but I can think of no other explanation that makes sense.
So, I assumed they were facing the same direction because they at least appeared to be looking in the same direction, but they weren’t. Not quite.
Ron
Notes:
- I’m still thinking that it’s all more complicated than I’ve stated above. Owls can’t move their eyes within their heads, they can only move their heads. So if they were all looking straight at me their head angles should be exactly the same but they don’t appear to be. So I’m still at least a little confused. A little help from my friends?
- In another recent blog post I made a claim about the position of catch lights on the eye relative to the sun angle that several readers challenged. What I’m seeing in this photo suggests to me that those readers were right and I was wrong. Won’t be the first time…
Addendum: Several readers, including Porcupine below, are reporting (some with documentation) that owls dilate their pupils independently and voluntarily – something I didn’t know. Once again I’m learning a lot from my readers.
Always learn something here, love the photo too!
Wow! I’ve learned so much about owl ophthalmology this morning — fascinating! Your blog is like a box of chocolates…in the best possible way! 😀
And bonus: adorable Burrowing Owl youngsters (the one on the left looks like he’s saying, “Come at me bro!”).
Thanks, Marty. Believe me, I learn as much here as most everyone else.
Just confirming that owls, and some other birds, can voluntarily and independently control the size of their pupils. At times it can be used as a silent form of communication. The pupil size may differ as one eye looks nearby and the other looks in the distance, however, this is less so in owls whose eyes are always forward-looking. Birds can also close one eye and allow much of the brain so sleep while the open eye remains alert to danger to quickly fully awaken the bird as needed. Another consideration concerning reflections is that birds do not have spherical eyes. The forward portion of the eye is somewhat flattened at the periphery and rounded in the center. This is especially exaggerated in owls eyes where the front of the eye is much more tubular. The angle of reflection off of these eyes differs from a more spherical eye except right at the very forward-most portion of the eye.
Once again you’ve included some fascinating info in your comment, Dan. I should have guessed that birds sometimes use that technique for communication. Thanks very much.
Yes birds can dilate their eyes to focus. Louise Shimmel’s explanation is great. Having had parrots years before rehabbing wild birds I am very familiar with what is called pinning, as I started working with more types of birds just made sense other birds did it too. The only time it is concerning is when a bird, most often owls, has a “blown pupil”. It will not dilate down when light is shined in the eye, the bird has lost vision in the eye.
There is an bird ophthalmologist here in Utah.
May I add fantastic photo!
Of course you may, April. Any ol’ time you feel like it!
April, I’ve photographed a fair number of birds with blown, or partially blown, eyes. Including an adult Bald Eagle.
I think David’s suggestion that the center bird had just swiveled his head around to see what the “disturbance in the force” was (the photographer) is a more than reasonable explanation for the difference in pupillary size. It wasn’t until I read his comment that I realized we’re seeing that bird’s tail, not his belly! (So observant, eh?)
This has been a very fun and informative discussion … and big bonus with beautiful Burrowing Owls! 😎
Could be, Chris. It’s been far to long since I took the photo for me to remember.
I just adore these chicks. As an aside, I can’t believe I’ve been following your blog for so long. I am fairly sure I saw this as an original post. 😀
Time flies when you’re having fun, Arwen. At least I hope you are.
Oh you know…it will do in a pinch. 😀 😀 😀 😀 (AND? I can post again!)
Yes – Birds have voluntary control over the dilation/constriction of their pupils (has to do with smooth vs striated muscles in their eyes but that’s over my head). Some constriction is in response to light (we do use pen lights to check for pupillary light response after head trauma, as in humans) but they also dilate and constrict as part of focusing near and far. I’ve had a bird on my glove and have watched his eyes change size, even though the the head is immobile and its angle to the light hasn’t changed a bit, as the bird caught sight of something in the distance. Parrots’ eyes do what is called ‘pinning’ when they are excited or scared – they rapidly dilate and constrict their eyes. And though there is some consensual pupillary response (i.e., when you shine a light in the right eye, enough goes through the thin barriers between the eyes to have some effect on the left eye), it’s not huge. The eyes can have different sized pupils depending on where light is coming from. Since owls’ eyes are in the front of their face, they have more binocular vision than most birds – most birds can focus on different things with different eyes (SOME birds have some vision behind them, a woodcock for example, whose narrow head provides even some binocular vision to the rear!) – but I don’t know if owls can focus on different things with each eye. As Ron said, owls cannot move their eyes at all – most birds can move them a bit though not like we can.
And yes there are avian ophthalmologists … Sorry this is a bit stream of consciousness – just now having my first cup of tea.
“we do use pen lights to check for pupillary light response after head trauma, as in humans”
I’m so glad you included that bit, Louise. I’ve been wondering about it all morning.
Please, “stream your consciousness” here any time you like. We all learn from your generosity.
How could you have missed this, Ron. Clearly the explanation is that the lower two birds have been into their parents’ pot supply!
Silly me. I need to pay more attention!
I just sent you 2 pdf files.
Thanks Dave. I just got home. I’ll check them out soon.
Wow ! The stuff one learns in “Feathered Photography” ! Keeps
me coming back for more every morning .
Good. It keeps me coming back too. 🙂
Are there avian ophthalmologists? Actually I am seeing this in a whole different way. I think the one in the center is not one of the youngsters, but an older owl who is not as interested or concerned with your presence. Regardless of the reason for the dilated eyes it is an outstanding photo.
“Are there avian ophthalmologists?”
Everett, I imagine there are some vets who specialize in that area. Maybe…
Now that I think about it you may be right about the center owl being older.
One thing I noticed is the center bird’s body (not head) is oriented differently than the other two. So if he had been looking toward the light and then just recently turned his head toward you, perhaps his pupils just hadn’t adjusted yet. I’m assuming that, like in people, their pupil dilation is not instantaneous, but reactive.
I said away from the light. I meant toward the light. lol
I wondered the same thing, David (I changed what you said to what you meant to say).
Hmmmm! Only thing I can see is the 2 owls with widely dilated pupils have the other eye in deeper shade that the one with the constricted pupils. The right pupil on the one in the middle seems a little larger than the left. Got me! 😉 Interesting point Porcupine makes…..
Judy, Porcupine was right. See my addendum.
I do love learning from you and your commentators. And if I learn through owls it is a definite bonus.
I am looking forward to reading more comments – and to have an excuse to come back and ogle the owls.
Wow, you’re up late EC. Or early. I have a hard time keeping that straight… 🙂
I occasionally assisted a veterinary ophthalmologist when I was a veterinary technician. She performed a lot of cataract removals and lens implants on dogs, among other things. Like Porcupine, we were taught the same thing about Owl irises.
Thanks for that info, Lyle.
I’m not even sure what branch of science the question falls under (Biology? Geometry? Physics?), let alone hazard a guess, but I sure do love these liitle guys. Thanks for reposting!
Robyn, like much of science it’s an interdisciplinary question. Thank you.
Ron
If I remember correctly from long ago ophthalmology classes, owls can dilate and constrict their pupils voluntarily. So your youngsters in this picture may be showing their emotions as much as they are reacting to the sunlight.
Great photo. I like the fact that the youngest is a bit softer. As the baby brother he is a bit softer in more ways than one!
Porcupine
“owls can dilate and constrict their pupils voluntarily”
Really? I didn’t know that. If so that could account for a lot of things.
I’ve read that a number of different birds and some other animals can control the dilation of their pupils, and they can control each eye independently. I was first made aware of this in a photo of a bald eagle (not my photo, unfortunately) that was flying directly toward the camera, and the pupil in one eye (the one in the shade) was large, while the pupil in the other eye was small. Human eyes don’t work that way.
“Human eyes don’t work that way.”
They sure don’t.