Bird’s-Eye View

Scientists don’t know much about the why behind the avian eye. Their research has mainly focused on feathers. While we have some eye information for about 180 bird species, 98% of species remain unstudied.1 A 2023 study analyzing what we do know about our feathered friends’ eyes revealed that we have a lot more to learn.2

The research team examined pigments and structures in different iris colors. As in human eyes, melanin is at work in producing the colors of bird feathers and eyes, but it’s not the only factor. Carotenoids (pigments) also contribute. Melanin results in black, brown, gray, and reddish-brown colors while carotenoids make reds, yellows, and oranges.

Other color contributors include pigments (such as pteridines and purines), blood vessels, lipids (fatty, waxy, or oily compounds), collagen fibers, and cholesterols. Birds’ eyes can have just one of these or a combination.

Scientists aren’t entirely sure why birds have such varied eye colors, but the research team behind the recent study offered several hypotheses. Eye color could play an important role in signaling (indicating age or quality in males for potential mates) for some species, with vivid eye colors serving a similar purpose as showy feathers. Some studies suggest that eye color could be associated with camouflage, as day-roosting birds have darker, less noticeable eyes.

Bright eyes could also help birds make their presence known. For example, jackdaws’ piercing blue-gray eyes discourage rivals from approaching their nests. Scientists also acknowledge that a bird’s eye color could simply be a result of their chemical makeup, without any function other than beauty. For that matter, the purpose of color could differ among species.

Studies of bird feather coloration have led to a greater knowledge of speciation in animals. This knowledge could be expanded further by researching the vast variety of eye colors. Whatever the reasons for the rainbow of bird irises, one thing’s for sure: All the incredible variety we see in creation points to an ingenious Creator who knew exactly what each creature would need to thrive in our fallen world. When we keep a lookout, we’ll see evidence of his colorful designs all around us—often staring us right in the eye.

Eye Color Among Passerines

Passerine birds are from the order Passeriformes, the largest order of birds today. Passerines include 6,500 identified species, including familiar ones like finches, sparrows, wrens, and crows. Known as perching birds, they are almost all distinguished by their anisodactyl toes, with three toes directed forward and one toe directed backward, which enable them to perch easily on branches.

Different birds might share a certain eye color, but that color can be created by different structures in the different birds. For example, red-eyed vireos have red eyes created by pteridines, while bronzed cowbirds have red eyes caused by the dilation of blood vessels in the eye.

Looking at Lashes

Male birds flash their feathers, bust a move, and build striking structures to impress the ladies—but few female birds bat their lashes in flirtatious return. Most bird species don’t actually have eyelashes.

Unlike most mammals, birds’ lashes aren’t made of modified hairs. They’re made of modified feathers, ranging from short and fine to long and, well, feathery. Bird eyelashes protect the eyes from debris when they fly, run, and burrow.

Eye protection for most birds comes from their nictitating membrane (inner eyelid), which both protects and moisturizes the eye—an important feature on long migrations or during dives in water. But birds with eyelashes tend to be large ground-dwellers.

Bird Eye Color Varies Within a Species for Several Reasons

• The eye color of some birds darkens or lightens as they age, possibly to signal adulthood. The color shift could help females gauge the maturity and quality of potential mates.
• Twenty-four species of birds have differing eye color between sexes.
• Several species of birds have eye colors that change during breeding season.
• Birds of the same species can have varying eye color based on where they live.

Sight for the Birds

From pink flamingos to indigo buntings, birds come in all colors of the rainbow. But the colors birds can be doesn’t compare to the colors birds can see.

Because bird retinas have more color cones than our retinas have, birds can perceive parts of the ultraviolet (UV) spectrum that are invisible to human eyes. The colors of their feathers represent a mere 26–30% of the colors birds can see. Additionally, the extra cones in bird eyes contain droplets of oil that filter wavelengths. This allows birds to see subtle differences in shades that we can’t.

God designed some flowers, fruits, and berries to reflect UV colors, so being able to see these hues might help birds find food. Also, some birds have patches of feathers that reflect UV light, colors that can attract potential mates.

Human eyes are undoubtedly well-designed by a brilliant Creator, capable of seeing a dazzling spectrum of color. But for us, ultraviolet colors are out of sight. Seeing those shades is indeed for the birds.

Cormorants

Cormorants wouldn’t win an award for most colorful feathers, but they might take the prize for boasting the widest variety of eye colors.