Importance of Color Vision in Birds
From the shimmering hues of a Hummingbird’s feathers to the rainbow colors of a Painted Bunting, avians are among the most colorful creatures in the natural world. Without color vision, their fancy feathers would be meaningless since they help birds recognize members of their species and gather important information like the age, sex, and fitness of other individuals.
Color vision also plays an essential role in finding food and prey and in detecting danger. Birds can see all the same colors we can, but they also perceive many colors outside of our visual range. The world must look very different through the eyes of a bird!
There’s much more to learn about the importance of color vision in birds. Read along as we delve into this fascinating field of bird biology!
The Basics of Color Perception
Cones and Photopigments
Birds have two major types of photoreceptors in their retinae. Rod cells are most sensitive to light and are dominant in the eyes of nocturnal birds like Owls.
Cone cells are color-sensitive and make up three-quarters or more of the receptor cells in diurnal birds. These birds have four types of color-sensitive cone cells, each sensitive to a different range of frequencies.
Avian Cone Cell Types:
- Long-wave-sensitive cones (Red)
- Medium-wave-sensitive cones (Green)
- Short-wave-sensitive cones (Blue)
- Violet or ultraviolet-sensitive cones
Before reaching the photopigments of the cone cells, light passes through an oil droplet, which varies in color depending on the type of cone cell involved. These clear or colored oil droplets filter out specific light wavelengths.
A female (left) and male (right) Painted Buntings. From the shimmering hues of a Hummingbird’s feathers to the rainbow colors of a Painted Bunting, avians are among the most colorful creatures in the natural world
Ultraviolet (UV) Vision – A Secret Spectrum
Seeing the Invisible
The presence of ultraviolet-sensitive cones allows many birds to perceive colors outside of the visible light spectrum that we can detect.
Many plants, animals, and objects reflect light in these very short wavelengths, so birds can see a lot of patterns and signals invisible to the human eye.
Role in Mating and Social Interactions
The fact that birds can see colors that we cannot opens up the exciting possibility that many of the birds we know look completely different through the eyes of avians.
Bird species that appear sexually monomorphic (males and females appear the same) may have clear differences when viewed through the avian eye, and species that already look colorful to us may have even more exotic plumage than we can imagine!
Of course, colorful plumage has evolved for some very important reasons. Many species rely, at least partly, on color characteristics to communicate their maturity, fitness, and genetic compatibility to a potential partner. So, there may be a whole range of ultraviolet markers that we aren’t yet aware of.
A pair of Blue Jays. Bird species that appear sexually monomorphic may have clear differences when viewed through the avian eye
Color in Communication and Behavior
Territorial Displays
Colorful male plumage is great for attracting a partner, but it also comes in handy for fending off competitors of the same sex. Red-wing Blackbirds (Agelaius phoeniceus) and many other species use their showy plumage to display and defend their territory.
Camouflage and Mimicry
Bird coloration isn’t always about showing off. Most species have more subtle colors, and many are cryptically camouflaged in natural, earthy shades of brown and gray to blend in with their environment. However, some birds use color to communicate with potential predators rather than to hide from them.
The Hooded Pitohui (Pitohui dichrous) is a rare example of aposematic coloration in birds. These poisonous, orange and black songbirds advertise their chemical defense with bright warning colors, just as many other toxic creatures do.
The Cinereous Mourner (Laniocera hypopyrra), a gray-brown songbird from South America, uses Batesian mimicry to pretend to be poisonous. The chicks are bright orange and covered in hair-like plumage that makes them look just like a toxic caterpillar. They even move like caterpillars to complete the act!
Parent-Offspring Interactions
The chicks of many bird species have colorful mouths to encourage their parents to feed them and possibly to guide them in the dim light of cavity nests.
When the parent bird returns to the nest, the chicks open their mouths widely to beg for food, often showing off bright yellow or red interiors. The young of some finch species take this form of color communication to another level by growing strange, colorful growths around the edge of their mouths.
Some birds reverse the trend by having colorful bills as adults. Herring Gulls and many other species in the Larus genus have bright red spots on their beaks that the chicks peck at when begging for a meal.
Red-wing Blackbirds and many other species use their showy plumage to display and defend their territory
A herring Gull with its chick. Many species in the Larus genus have bright red spots on their beaks that the chicks peck at when begging for a meal
Navigational Aids and Food Detection
Spotting Resources
Improved food detection is one of the major benefits of color vision for birds. Many plants benefit from birds that eat their fruits and disperse their seeds or even pollinate their flowers. Birds detect these sugary foods by their colors, as bright flowers and colorful berries tend to stand out against green foliage.
Scientists have discovered that some food sources reflect ultraviolet light, making them highly visible to birds. Ripe fruits, markings on flowers, seeds, and even flying insects may all show up much more clearly to the avian eye than to our own.
Colors also tell birds what not to eat. Many insects, frogs, reptiles, and other prey animals have bright warning coloration to deter birds and other predators. These distasteful or toxic creatures typically show off colors like black, white, yellow, orange, and red.
Environmental Cues
Color vision also helps birds gather information about their environment. A migrating bird may identify important markers in the landscape that guide its journey, and the changing color of vegetation, as plants come out of dormancy in spring and die back in the fall/autumn, can tell birds when to start their migrations.
A Fieldfare. Many plants benefit from birds that eat their fruits and disperse their seeds or even pollinate their flowers
Evolutionary Implications of Color Vision
Natural Selection and Color Vision
From finding enough food to stay alive to choosing a healthy partner in the breeding season, color vision has obvious benefits for diurnal birds. However, birds did not evolve color vision but rather inherited it from earlier ancestors.
Interestingly, the ability to see in ultraviolet was lost at some stage but has re-evolved during the evolutionary history of birds.
Adaptations Over Time
Since they first appeared over 150 million years ago, birds have evolved to inhabit every continent and thrive in habitats as diverse as polar oceans, tropical rainforests, and desolate deserts. This diversity of habitats and ecological niches has put selective pressures on bird lineages for different visual adaptations.
Eagles, for example, have evolved the most powerful diurnal color vision of any animal on the planet, while Owls have forfeited UV vision for extremely sensitive rod-dominated retinas.
As new species evolve and others are lost to extinction, birds and their vision continue to adapt and specialize to the demands of their lifestyle.
A female Snowy Owl. Owls have forfeited UV vision for extremely sensitive rod-dominated retinas
Summary
Selection for powerful vision has shaped the avian eye into the most advanced sight system in the natural world, and color vision is a huge part of their success.
The ability to detect a ripe berry among dense foliage, avoid a toxic snack, or judge the genetic fitness of a potential partner merely by looking at their plumage color are just some of the secrets that have made birds the most diverse group of land animals on the planet.
We may never see the hidden patterns in flowers, the ultraviolet reflection of a ripe berry, or even the true range of plumage colors on a male songbird bird in breeding color.
However, we can all admire the super senses of our feathered friends and appreciate the vibrant colors they bring to the world!