Birds can see color differently than humans do. Their vision is tuned to detect specific colors that are important for finding food, choosing mates, and avoiding predators. While birds can see a wide range of colors, there are certain colors that birds tend to avoid for various reasons. Understanding what colors birds see and how their vision differs from human vision can provide insight into avian behavior and ecology.
How bird vision differs from human vision
Human color vision is trichromatic, meaning it utilizes three types of cone cells to detect different wavelengths of light corresponding to red, green, and blue. Bird vision is tetrachromatic, meaning it uses four types of cone cells to detect light. The four cones allow birds to see ultraviolet light in addition to red, green, and blue.
Birds also have oil droplets in their cone cells that act as filters to fine-tune the wavelengths of light entering the eye. Different oil droplets in each cone allow for more precise color discrimination. The combination of an extra cone type and filtering oil droplets means birds can distinguish many more shades across the light spectrum compared to humans.
Some key differences in how birds see colors:
– Birds have better color resolution and can detect slight variations in hue that humans cannot.
– Ultraviolet wavelengths are visible to birds but not humans. Many birds use UV signals for mating displays.
– Red wavelengths appear darker to birds, while blue and green appear brighter.
– Some poisonous or unpalatable prey have color patterns detectable only in the UV range, acting as a warning signal to avian predators.
Colors birds avoid and why
While birds have excellent color vision, there are certain colors they tend to avoid when possible due to their visual capabilities and ecology.
Red
Red is difficult for birds to see clearly. Red light is attenuated at the red end of the avian visible light spectrum. Red objects have low chromatic contrast compared to other colors for avian viewers. Red blends into the foliage background, making it hard for birds to detect.
This can explain why few birds have red plumage. Most red birds such as cardinals and tanagers use red pigments along with yellow, white, or black markings to increase detectability. Birds are less likely to choose red items as visual signals or warnings. Few poisonous prey animals advertise themselves with red coloration.
Black
Black is also difficult for birds to see. While humans see black as a distinct color, the avian eye perceives black as extremely dark with an undefined hue. Black has low chromatic contrast against dark backgrounds for birds.
Black makes a poor signal color for birds, blending into the shadowed parts of trees and vegetation. Black food items are hard for birds to detect against dark soils or bark. Few birds have all-black plumage or markings. However, some species like crows and ravens utilize black for camouflage.
Brown
Brown sits in an uncertain part of the avian color spectrum. It has elements of low-contrast red, yellow, and black. Different shades of brown vary in their chromatic contrast level for birds. In general, brown hues offer camouflage similar to black, blending into woody and earthen backgrounds.
Species like sparrows and wrens use browns to remain undetected by predators. Brown provides useful environmental color matching, but it is not an ideal signal color for sexual or warning displays.
Ultraviolet spectrum
Ultraviolet wavelengths are visible to birds but not humans. While UV can serve some positive signaling functions, birds seem to avoid ultraviolet-dominant spaces. Strong UV light causes photokeratitis – a burning of the cornea that can lead to blindness.
Birds generally avoid open terrain, snowfields, sand, and water during bright sunlight when UV levels are highest. Extended exposure is physically harmful. Birds preferentially seek shaded and wooded habitats that filter the solar UV radiation.
Rapidly flickering light
Humans perceive fluorescent lights as steady illumination, but the rapid flickering is visible to birds. The flicker rate can produce a disorienting stroboscopic effect. Flickering light can induce seizures in susceptible parrots and other birds.
Extremely high flicker rates above 2-3 kHz are imperceptible and safer for birds. Otherwise, birds tend to avoid staying long in environments with lower frequency fluorescent or sodium vapor lighting if possible. The disorienting light risks colliding with walls or windows in such spaces.
Colors birds are attracted to and why
Specific colors attract avian attention and suit their visual capabilities. These colors are frequently used for signals, mating displays, warning coloration, and food sources.
Green
Vibrant greens are highly visible and attractive to birds. Green hues contrast strongly against natural vegetation for avian eyes. Bright green stands out as a signal color and helps birds spot potential food sources.
Many insects and fruit eaten by birds have a green coloration. Hence birds associate green with nutritious prey and will investigate green novel objects. Parrots are particularly attracted to green toys and objects.
Yellow
Yellow is also a high contrast, eye-catching color for birds. Many species such as warblers and goldfinches utilize yellow for plumage markings and displays. It provides strong visibility in shaded habitats.
Yellow/green foods like ripe fruits and caterpillars are appealing to birds. Vivid yellow flowers attract avian pollinators. Bright yellow feeders and birdhouses will attract wild birds to visit.
Blue
Blue is the color of open sky and water visible to avian viewers. While humans see blue as a single hue, birds can distinguish various shades of blue. Blue contrasts strongly against natural brown and green backgrounds.
Blue is used by jays, buntings, bluebirds and other species as signal coloration. Blue tits and swallows utilize cobalt blue plumage to attract mates. Saturated blue is eye-catching and indicates water sources and flying insect prey.
Purple/Violet
Purple and violet contain a mix of the red and blue wavelengths birds can detect. These hues contrast and stand out against green foliage. Violet gradients are common in avian plumage, such as on pigeons.
Many flowering plants utilize violet as an attractant color for avian pollinators. Birds associate rich purples with ripe berries and fruit. Unique purple feeders and houses will attract wild birds.
White
A pure white is highly visible to birds, contrasting against most backgrounds. Many species feature white wing patches, tail bands, or facial markings for signaling. White shows well at a distance through dappled shade.
Birds recognize white as signaling safety and comfort. Seagulls are attracted to white boats where food is abundant. Pigeons and doves mob pale gravel rooftops. Bird species will readily approach white feeders and nest boxes.
How birds detect color
Birds have excellent color vision suited to their ecology and signaling needs. This is enabled by the architecture of the avian eye:
Four cone types
Birds have four types of cone cells for absorbing light:
– Long wavelength sensitive cones detect red, orange and yellow
– Medium wavelength sensitive cones detect green
– Short wavelength sensitive cones detect blue and violet
– Ultraviolet sensitive cones detect near ultraviolet and some purple
Oil droplets
The cones contain colored oil droplets that fine-tune the wavelengths entering. Oil droplets act as filters to narrow the spectral sensitivity of each cone. This allows finer color discrimination.
Double cone structure
Avian cones have two inner segments joined together. These double cones allow each cone type to compare wavelength sensitivity and detect subtle hue differences.
More cones than rods
Birds have approximately 1.5-2.5 times more cones than rods compared to humans. This indicates excellent photopic (daytime) vision and color detection. Birds have fewer low-light sensing rods.
High visual acuity
Raptors and other species have very high visual acuity, enhanced by extra foveae focus points and more retinal ganglion cells. This allows sharp color discrimination of small, distant targets.
Differences across species
Color vision capabilities differ somewhat between bird groups evolved for various habitats:
– Raptors have high acuity focused on detecting small prey
– Waterfowl see well across water and air environments
– Forest birds distinguish complex green hues
– Shorebirds visualize contrast on beaches and mudflats
Conclusions
In summary:
– Birds have tetrachromatic vision and see more color shades than humans
– Oils droplets in cone cells fine-tune avian color detection
– Birds avoid red, black, and UV-dominant habitats when possible
– Green, blue, yellow, white and violet attract birds and serve as signal colors
– Cones and high acuity facilitate excellent avian color discrimination
– Color detection is adapted to species ecology and signaling requirements
Understanding the avian visual system provides insight into bird behavior, evolution, and sensory ecology. Additional research is still needed into how different species perceive and respond to various colors in their environment. But it is clear birds have a sophisticated use of color vision essential for their natural history.
