Bird Eye Color

Summary: Have you ever noticed how many different eye colors birds have? Join Kiersten and Cheryl as they delve into this understudied topic.

 

For our hearing impaired listeners, a transcript of this podcast follows the show notes on Podbean.

 

Show Notes:

“Bird Eye Color” A Rainbow of Variation, a Spectrum of Explanations,” by Eamon C. Corbett, Robb T. Brumfield, Brant C. Faircloth. https://ecoevorxiv.org/repository/object/3682/download/7316

“Bird Eyes Come In an Amazing Array of Colors – but Why is a Mystery,” by Meghan Bartels; Audubon February 2023. www.audubon.org

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Kiersten: Intro: Eye color in birds is often something we might overlook. But it’s incredibly fascinating. Bird’s eyes come in a variety of colors and can even vary throughout one individual’s life. Today Cheryl and I are going to talk about eye color in birds.

 

Cheryl: We all know how colorful bird’s feathers appear. They can be blue, red, yellow, even green. This is one of the reasons birds have been studied by scientists for so long and one of the main reasons we want to attract birds to our backyards. We want so see those bright, fabulous colors. Scientists want to know what’s up with all the colorful feathers, and while this is fascinating and important research, it has overshadowed the other amazing colorful characteristic of birds: their eyes.

            Here in the southwest, the Curve-billed Thrasher, is an example of bird with a brightly colored eye. Adults have bright orange eyes. It’s an iconic characteristic and a great way to distinguish them from other types of thrashers.

            Birds’ eyes come in many different colors from dark-brown to light-brown to reds, oranges, yellows, greens, blues, and even white. Within these colors, a range of hues exist such as the turquoise of the Double-crested cormorant, the emerald green of the Black-and-red Broadbill, the crimson red of the Bronzed cowbird, the sunset orange of the Painted buttonquail, and the school bus yellow of the Short-eared owl.

            Birds even have multi-colored irises. Our Curved-billed Thrasher’s orange eye is actually a combination of an outer ring of orange with an inner ring of yellow to red near the pupil. The underappreciated Rock Pigeon actually has a beautiful eye with a ring of red on the edge and a ring of yellow around the pupil. The Greater Roadrunner, another of our southwest residents, has an eye with rings of brown and yellow around the pupil. Most of the birds with multi-colored iris have symmetrical coloration, but a few have asymmetrical coloration.

            The Bank Cormorant’s eye is an earthy orange on top while the bottom looks like a turquoise stone. Looking at this bird’s eye is like looking at an Arizona sunset. Some female oystercatchers have dark eye flecks on only one side of the pupil giving their eye a keyhole appearance.

 

Kiersten: It is amazing the colors that are found in the avian world, but the light bright colors are less prevalent than the darker colors. A study released early this year, in 2023, has compiled information previously researched about eye color and they noticed some trends.

            It appears that more birds have darker eye color, such as brown and black, than light eye color. Birds, as a whole, have darker eyes on average than other vertebrate groups including mammals, reptiles, and amphibians. Looking at passerines, such our songbirds, 64% had black to dark brown eyes, 19% had light brown to red eyes, and 17% had the lightest eye colors including yellow, orange, white, pink, blue, and light gray.

            Non-passerine birds, such as hawks, owls, ducks and other water birds, have lighter eyes than passerines. 40% were dark, 22% were the intermediate light browns and red, while 38% were light. The dark versus light hues found in birds do tend to follow phylogenetic lines. Birds in related families tend to have the same level of eye color. They may not always have the same eye color exactly but they are often categorized the same as dark, medium, or light. What we’ve talked about so far is differences of eye color between species but there are differences in eye color within species.

 

Cheryl: There are typically three reasons eye color will vary within a species. Number 1: Some birds are born with a darker eye color that will lighten as they age. For example, our Curve-billed Thrasher is born with brown eyes that change to orange only when they are adults. Spotted towhees have dark brown eyes as juveniles that turn red when they are adults. Osprey chicks are born with orange eye