Thanks to UV vision, birds see the world very differently than we do
- Cynthia Berger
- Jul 19, 2012
IN THE EARLY 1970s, A RESEARCHER testing the ability of pigeons to discriminate colors discovered by accident that the birds can see ultraviolet (UV) light. The finding was deemed curious but not too important. “It was natural for scientists to assume that bird vision is like human vision,” says Geoffrey Hill, an Auburn University ornithologist and the author of Bird Coloration. “After all, birds and humans are both active by day, we use bright colors as cues. ... No one really imagined birds might see the world differently.”
But during the following decades, systematic testing of bird vision revealed something unexpected: Many bird species—not just pigeons—can see UV light. Indeed, with the exception of night-flying birds such as owls, the eyes of most birds probably are even more sensitive to ultraviolet light than they are to what we call visible light. Scientists also have learned that many birds have plumage that reflects UV light. Together, these discoveries “made us realize there could be new answers to old questions,” says Drake University biologist Muir Eaton. Birds rely on vision to choose mates, find food and scan for predators, for example. “If you assume birds see exactly what we see, you could have the wrong framework for understanding bird behavior,” Eaton says.
Consider how birds choose mates. “After the first studies on birds and UV came out, people started saying, ‘Maybe your study of mate choice isn’t valid because you scored the feather colors with the naked eye,’” says Peter Dunn, a University of Wisconsin–Milwaukee biologist who studies active little warblers called common yellowthroats (below). Adds Hill, who has researched mate choice in house finches, bluebirds and indigo buntings: “When I started working, back in the 1980s, we used to hold up color charts against the birds’ feathers”—the same square paint chips that are an industry standard for graphic designers and interior decorators.
During the past three decades, a flurry of studies has tested the intriguing notion that mate choice and other bird behaviors may be shaped by secret visual signals humans cannot see. Though the premise was exotic, what facilitated this explosion of research was prosaic: Technology got better and cheaper. In particular, the increased availability and decreased cost of a lab device called the spectrophotometer—which precisely measures light reflected or absorbed by a surface—let scientists, if not see like a bird, at least quantify what birds are seeing.
Initially, many researchers turned their spectrophotometers on birds that do not use flashy feathers to attract mates. A team of Swedish scientists, for example, looked at the blue tit, a European relative of the chickadee. As with many bird species, male and female blue tits look alike to humans. “Standard literature describes the plumage as closely similar between the sexes,” says Staffan Andersson, a professor of animal ecology at the University of Gothenburg. “The main problem with this conclusion is that it is based on the UV-blind and yellow-biased human eye.” Using a spectrophotometry probe to scan the feathers of wild-caught birds, Andersson and his colleagues discovered that blue tits themselves have no problem telling males from females: Males have a patch of feathers on the crown of the head that strongly reflects UV light; females do not.
Blue tits are not alone. In 2005, Eaton used a spectrophotometer to scan the plumage of museum study skins of 139 songbird species in which males and females appear alike, from cedar waxwings to barn swallows to mockingbirds to western meadowlarks. Though scientists previously had classified these birds, along with 70 percent of all songbird species, as sexually monochromatic (males and females looking identical), a full 90 percent of the species Eaton scanned actually were sexually dichromatic: different once you took into account the better discrimination of colors (including ultraviolet) by birds and the amount of UV light feathers reflect. “To the birds themselves, males and females look quite different from one another,” Eaton says.
Such findings led some researchers to speculate that the primary role of avian UV vision is to select mates. Indeed, in laboratory tests, Andersson and his colleagues found that female blue tits strongly preferred males with the brightest “invisible” crowns—evidence that the UV-reflecting feathers humans cannot see were serving their function.
Over time, however, scientists have concluded that blue tits are the exception to the rule. Very few bird species use UV light only—with no other visual cues—to attract and choose mates. “In general, ultraviolet reflectance simply reinforces the plumage color patterns we humans already can see,” says Dunn. Among his study subjects, “yellowthroat females do prefer males that are brighter, but not because of the UV reflectance alone. It’s more the brightness of the feathers overall.”
Foiling Nest Parasites
So, how do birds use their power of UV vision? In a surprising number of ways, scientists propose. Many songbirds, for example, are pestered by nest parasites: birds such as cuckoos and brown-headed cowbirds that dump their eggs in a host nest and leave the hard work of childcare to the unwilling adoptive parents. It turns out that some potential hosts are able to recognize and reject eggs that, to human eyes, look like their own. Might birds be responding to UV signals rather than to colors visible to people?
The evidence so far is suggestive but inconclusive. In one 2007 study in the Czech Republic, song thrushes rejected experimental eggs researchers had designed as perfect mimics. It turned out the scientists’ eggs had a UV reflectance different from the thrush eggs. But a Canadian study of 11 species parasitized by cowbirds found no correlation: Some species accepted eggs that were a UV match; others rejected them.
Signals From Hungry Chicks
Scientists also are investigating whether UV signals play a role after eggs hatch. Think of hardworking parent birds, ferrying caterpillars to a nestful of hungry chicks. Which chick gets fed first? In some species, parents cue in on a hatchling’s size or how loudly and energetically it begs. But color also is a factor—the brightness of the gape (edge of the mouth) or the head seems to stimulate a parent to proffer food. Some researchers suggest UV color may enhance this effect.
Newly hatched European rollers, for instance, have a patch of bare skin on the foreheads that reflects UV light. Their parents face a particular challenge as they dole out centipedes and other treats: Because roller clutches hatch over a period of days, first-hatched chicks are larger and need more food than chicks that hatch later. In a 2011 study, Spanish researchers noted that heavier chicks tend to have the least UV-reflective forehead patches; lighter chicks had more reflective foreheads. To test whether this difference helps parents decide who to feed the most, the scientists smeared a sunblocklike lotion on the foreheads of some chicks, using a control lotion on others. The chicks with the blocker gained less weight than their unblocked nestmates—clearly showing they got less food when they could not advertise their nutritional status with UV signals.
Parent birds may rely on UV signals when they’re off finding food as well. Many insects, including moths and butterflies, have body coatings that strongly reflect UV light. Many seeds also are reflective, and berries and fruits develop a highly reflective waxy coating as they ripen. On the other hand, most green leaves do not reflect UV light. So even if a red berry seems quite visible against a green leaf to human eyes, for birds this contrast is enhanced.
“I think the biggest thing to come from the discovery that birds see in the ultraviolet is our understanding of how some predatory birds find their prey,” says Hill. Picture, for example, a kestrel (American kestrel, right) perched high on a telephone wire, surveying a field far below. “I always wondered how a bird of prey gets enough to eat,” he says. “After all, you can walk through a grassy field 20 times and never see a mouse.”
But that’s because we do not see what the birds see. It turns out that one key prey for common kestrels, the meadow vole, behaves like a tiny dog, using squirts of urine to mark its trails through tall grass. About 15 years ago, Finnish researchers from the University of Turku discovered that vole urine reflects UV light—which kestrels soaring over open fields can plainly see. “Once you realize raptors can follow the trail right to the animal, it makes a lot more sense,” Hill says.
Indeed it does. While people long have wondered what it would be like to soar like a bird, the more interesting question—particularly for biologists—may be: What would it be like to see like a bird?
Cynthia Berger is a Pennsylvania-based writer and the former managing editor of Living Bird magazine.
Birds and UV Light: The Eyes Have It
How do birds detect ultraviolet (UV) light? To answer this question you must understand avian eye structure. The human retina has three kinds of cone cells (receptors used for color vision): red, green and blue. By contrast, birds active during the day have four kinds, including one that’s specifically sensitive to UV wavelengths. There’s another difference: In birds, each cone cell contains a tiny drop of colored oil that human cells lack. The oil drop functions much like a filter on a camera lens. The result is that birds not only see UV light, they are much better than humans at detecting differences between two similar colors.
What does the world look like to a bird with UV vision? “We can’t imagine,” says Auburn University ornithologist Geoffrey Hill. Since birds can detect more colors than humans can, scenes may appear more varied. And colors that already are bright to human eyes are—if amplified by UV reflectance—probably even brighter to birds.
Bird Research Yields Consumer Products
In the grand U.S tradition, entrepreneurs are beginning to capitalize on new knowledge about bird vision to invent clever consumer products. Here are a few examples:
A Better Duck Decoy: Waterfowl hunters know that the more realistic a duck decoy is, the better it works. A life-long duck hunter, ornithologist Muir Eaton notes, “When I got into this UV research, I said, ‘Holy moly, I should invent UV-reflecting paint for my decoys!’” Someone beat him to it. Most major manufacturers of mass-produced decoys now offer UV-reflecting paint as an option on their products.
Avoiding Collisions . . . and Cats: Each year up to 1 billion North American birds die after colliding with windows, says Muhlenberg College researcher Daniel Klem. One way to warn birds that an invisible but solid barrier blocks their flight path is to decorate windows with decals. “But that’s hardly visually satisfying,” Klem notes. A more pleasing option for consumers would be windows that reflect UV light—visible to birds but not people—a project Klem is working on and hopes to convince manufacturers to produce commercially. Hundreds of million of birds also fall prey each year to outdoor cats. One entrepreneur is capitalizing on birds’ ability to see UV to combat the problem by marketing a collar that claims to make feline predators more visible to birds.
Camouflage Clothing for Birders: Some avid bird-watchers are reconsidering their fashion choices now that they know birds see in the UV. Many modern clothing dyes reflect UV, as do the “brightening” agents in some detergents. Today birders can choose from a variety of sprayable fabric treatments that will make their favorite jackets less showy as the clothing absorbs (rather than reflects) UV wavelengths.
Goose Be Gone: A flock of Canada geese winging overhead can be a prelude to a mess. One way to repel so-called “nuisance” geese is by spraying the grass with a bad-tasting but harmless chemical derived from grapes. Research shows this treatment is even more effective when coupled with a second spray: a compound that reflects UV light. Invisible to human eyes, the spray makes a swath of treated grass quite obvious to geese, a visual cue that reinforces the lesson, “This food tastes bad—stay away.”
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How do birds see the world as compared to humans? ›
For unlike humans, birds can perceive wavelengths in the ultraviolet as well as the visible range of the spectrum. So a bird is able to see ultraviolet “colors” in another bird's plumage that humans cannot.How many more colors can birds see than humans? ›
While humans have just one nonspectral color—purple, birds can theoretically see up to five: purple, ultraviolet+red, ultraviolet+green, ultraviolet+yellow and ultraviolet+purple.What colors can birds see that we cant? ›
While humans have three color-detecting cones in their eyes — to see red, green and blue shades — birds have a fourth cone that enables them to see ultraviolet (UV) light. This permits birds to see a broader spectrum of colors than humans.How does a bird see the world? ›
Binocular vision means both eyes focus on the same object at the same time, and eye movement is coordinated – this is the kind of vision that predatory birds such as owls rely on most. Monocular vision means each eye is focused on a different object at any particular moment, and this is normal for parrots and pigeons.Do birds know we are human? ›
Although many wild birds have been documented, both scientifically and anecdotally, to recognize humans, certain birds are more known for it. Crows, magpies, pigeons, robins, mockingbirds, and jackdaws have some of the most well-documented cases of facial recognition.Do birds see the same colors as humans? ›
Ironically, the answer is that birds see many more colors than humans can, but birds are also capable of seeing many more colors than they have in their plumage. Birds have additional color cones in their retina that are sensitive to ultraviolet range so they see colors that are invisible to humans.What animal has the best eyesight? ›
Mantis shrimps probably have the most sophisticated vision in the animal kingdom. Their compound eyes move independently and they have 12 to 16 visual pigments compared to our three. They are the only animals known to be able to see circular polarised light.What animal sees the most colors? ›
Here are some other incredible eyes in the wild: The critter with the world's best color vision (as far as we know) is the bluebottle butterfly. Where we have three different types of cones to detect color, they have a whopping fifteen, some of which see in the UV spectrum.What color is most visible to birds? ›
Blue. "Bluebirds and Blue Jays tend to be attracted to blue," says Johnson. This is partly because birds seem to be attracted to their own color. So, if you want to attract birds that come in a variety of blue shades, you can incorporate more blue into your backyard with flowers and bird feeders.What color do dogs see? ›
Human eyes have three types of cones that can identify combinations of red, blue, and green. Dogs possess only two types of cones and can only discern blue and yellow - this limited color perception is called dichromatic vision.
Do birds have a favorite color? ›
These two young, future scientists believe that birds prefer colors in the high energy wavelengths—blue, purple, and green. Red and yellow, low energy wavelength colors, they believed, were less popular because they are warning colors in nature.Why can't birds see in the dark? ›
The performance of the eye in low light levels depends on the distance between the lens and the retina, and small birds are effectively forced to be diurnal because their eyes are not large enough to give adequate night vision.Can birds see emotions? ›
Parrots are very sensitive to our emotions, sometimes better than we are. Our birds are keen observers of our facial expressions, body language, tone and even energy levels and therefore we have to be cognizant of how our emotions can impact our birds.How do birds sense humans? ›
The myth derives from the belief that birds can detect human scent. Actually, birds have relatively small and simple olfactory nerves, which limit their sense of smell. There are very few birds with extraordinary olfaction and these represent specialized adaptations.Do birds know where they are going? ›
Birds can get compass information from the sun, the stars, and by sensing the earth's magnetic field. They also get information from the position of the setting sun and from landmarks seen during the day. There's even evidence that sense of smell plays a role, at least for homing pigeons.Can birds feel feelings? ›
The evidence reviewed in this section is consistent with the hypothesis that at least some avian species experience emotional states akin to mammalian fear. The behavioral, neurobiological, and psychopharmacological results reviewed above suggest interesting parallels between mammals and birds in emotional behavior.Do birds love humans? ›
Few birds develop an emotional relationship with human beings, instead of attachment with other animals. They often return their feeling of love to a human. This is not a materialistic but an emotional attachment.Do birds hear human voices? ›
New research suggests that some birds may know who their human friends are, as they are able to recognize people's faces and differentiate between human voices. Being able to identify a friend or potential foe could be key to the bird's ability to survive.Do birds have good memory? ›
Lab research on Clark's nutcrackers and chickadees has also found that the birds can remember the locations of hundreds of seeds for six months or more. “All animals have some basic memories,” he says, “and we may underappreciate how good . . . even [basic] memory is.”Can birds see in the dark? ›
All birds can see at night to some degree, but there are some species that have evolved anatomical features that give them an advantage in seeing in low light conditions. Night vision is essential for birds that hunt or migrate at night.
What do birds see when they look at you? ›
Birds are what are known as tetrachromats, meaning they see four colors: UV, blue, green and red. By comparison, we humans are trichromats and can only see three colors: blue, green, red.What animal should you not look in the eye? ›
If you encounter an aggressive lion, stare him down. But not a leopard; avoid his gaze at all costs.What is the smartest animal on the world? ›
CHIMPANZEES. RECKONED to be the most-intelligent animals on the planet, chimps can manipulate the environment and their surroundings to help themselves and their community. They can work out how to use things as tools to get things done faster, and they have outsmarted people many a time.What animal has the weakest eyesight? ›
National Geographic has the answer: 15 feet. Even though rhinos can charge up to 30 miles per hour, they can't distinguish between a human and a tree at 15 feet. Unless rhinoceroses can clearly hear and smell you, they have no way of knowing where you are in physical space.
Blue is one of the rarest of colors in nature. Even the few animals and plants that appear blue don't actually contain the color. These vibrant blue organisms have developed some unique features that use the physics of light.How do dogs see humans? ›
In other words, dogs may notice our faces, and even the expressions on them, but they use all sorts of other information, such as body language and voice cues, to tell what we are up to. Humans, on the other hand, value most what they see on a face.Which animal has the best hearing? ›
Bat. Bats are known for having the best hearing of all land mammals. Their front limbs have adapted into wings and they are known for their excellent flying ability. Bats use their hearing and a process called echolocation to detect prey and objects when flying.Do birds prefer sun or shade? ›
A sheltered southeastern exposure is best for hanging a bird feeder since birds like to feed in the sun and out of the wind. Birds also prefer to have a clear view over their feeding area so they can see any predators.Do birds prefer light or dark? ›
This study suggests not only that urban birds can get used to the lights of the city, but also that birds actually prefer to have – at least a little – light at night.What colors do humans see? ›
As we mentioned above, the human eye has three types of cones that allow us to see a certain range of light and, therefore, colour, on the electromagnetic spectrum – i.e. the visible light spectrum. These colours are blue, green, and red. But obviously, we see much more than just these three colours.
Why do dogs lick you? ›
Licking is a natural and instinctive behaviour to dogs. For them it's a way of grooming, bonding, and expressing themselves. Your dog may lick you to say they love you, to get your attention, to help soothe themselves if they're stressed, to show empathy or because you taste good to them!How does dog laugh? ›
What does a dog laugh sound like? All laughter is a sound made by exhaling and inhaling air. Human laughter is made when the chest muscles squeeze air out of the ribcage, creating a vocalised, spoken “ha ha” sound. Dog laughter is created by panting without any vocalisation, creating a more “hhuh hhah” sound.Can dogs see TV? ›
Dogs absolutely can see TV, and many seem to enjoy it. There are a number of features about television shows that dogs find attractive. Some of these are visual, such as motion, while others relate to the sounds coming from the TV. Dog eyes are very different from human eyes, so they see things on TV differently.What do birds love the most? ›
- Bird seed.
- Seeds & nuts.
- Bird cakes.
- Live foods.
- Dog & cat food.
- Rice & cereals.
- Fats & oils.
- Milk & coconut.
Hummingbirds are little creatures, so they are wary of any loud noises. Loud music, children, or barking dogs can all scare them away. If you want to provide a safe haven for them, keep noise to a low and see if that does the trick.What is a calming color for birds? ›
When you're designing your bird's nesting area, choose neutral tones like green, yellow, and blue to avoid any colors that might be alarming to them.Do birds sleep at night? ›
Nocturnal birds, like owls and nighthawks, wake up as the sun sets and hunt at night. During the daytime, they find a safe place and close their eyes to block out the light. By contrast, most birds are diurnal, meaning they're awake during the day and asleep at night.Why can't birds see windows? ›
“Birds see differently from humans,” Martyn says. “They don't perceive glass as a solid object. To them, it could look like you could fly straight through the glass to the other side. Or, the glass reflects the landscape, sky or water, and it looks like the landscape continues on, so they might fly straight into it.”Why do birds drop dead in dark? ›
Startled birds flee from the forest en masse, but the following electromagnetic pulse disrupts their sense of balance during flight, causing them to fall to their deaths.Do birds mourn their dead? ›
Let's let John Marzluff, noted corvid researcher at the University of Washington, have the last word: "Birds certainly possess the capacity to mourn — they have the same brain areas, hormones and neurotransmitters as we do, they can feel what we feel"— but that doesn't mean we know when it's happening.
Do birds mourn the loss of a baby? ›
It's interesting to note that birds exhibit many of the grieving behaviors we do: their posture droops, they appear listless, and often cry real tears. Certain birds—jay birds, pigeons, and ospreys—will remain near where their baby died for long periods of time.Do birds feel pain? ›
From transduction to transmission, modulation, projection, and perception, birds possess the neurologic components necessary to respond to painful stimuli and they likely perceive pain in a manner similar to mammals.How do birds feel when you pet them? ›
There isn't one specific yes or no answer to this question. Some birds don't like being handled by their owners, but would rather spend time with them by playing games and just hanging out. Whereas other birds want nothing more than to sit on your lap and be gently scratched on the head.What do birds do when they like someone? ›
Love and affection: Gentle courtship behavior such as mutual preening or sharing food shows a bond between mated birds that can easily be seen as love.What is bird's strongest sense? ›
Sight: A bird's eyesight is the most important of its senses to its survival. Our bird's vision, while not as acute as that of raptors, is vastly superior to our own and is adapted to the survival needs of parrots.Where do birds go in the rain? ›
When bad weather hits, birds generally seek shelter from wind and rain in dense shrubs or thickets, next to heavy tree trunks, and on the downwind side of woods and forests. Cavity-nesting birds hunker down in nest boxes and natural cavities to ride out storms.Do birds know when something bad is going to happen? ›
Scientists believe it is the birds' ability to hear infrasound — low-frequency sounds inaudible to humans — that allows the birds to sense storms and tsunamis coming.What do humans look like in bird vision? ›
The graphic compares the human spectral field of vision to the bird's. As birds are tetrachromats, they see four colors: UV, blue, green, and red, whereas we are trichromats and can only see three colors: blue, green, red.Why can't birds see glass? ›
“Birds see differently from humans,” Martyn says. “They don't perceive glass as a solid object. To them, it could look like you could fly straight through the glass to the other side. Or, the glass reflects the landscape, sky or water, and it looks like the landscape continues on, so they might fly straight into it.”How do birds feel about humans? ›
The behaviour of closeness display that the bird has faith in you. Sometimes birds shake their tails to show their feeling of love to humans. They also sleep on you or on your arm, which means that they love you and have huge trust in you. Birds flap wings, their feathers without flying when you come to them.
What do birds think about humans? ›
Birds are typically afraid of humans because their instinct tells them humans are potential predators. We often make noises and movements that are unfamiliar to many wild birds. They can also sense our curiosity in them, which can be perceived as a threat if we are too close.Which animal has the best eyesight? ›
Mantis shrimps probably have the most sophisticated vision in the animal kingdom. Their compound eyes move independently and they have 12 to 16 visual pigments compared to our three. They are the only animals known to be able to see circular polarised light.Can birds see humans through glass? ›
Birds can't see glass. Instead, they see whatever happens to be reflected in its mirror-like surface. Often, this is open sky or trees, which, if you're a bird, are appealing (and perfectly safe) things to fly towards.Do animals know we see with our eyes? ›
A number of vertebrate species easily recognize the eyes of a human and "know" when they are being looked at. Highly social animals like dogs (and wolves) respond to this depending on the situation.Can birds see while flying? ›
"When in flight, birds may turn their heads to look down, either with the binocular field or with the lateral part of an eye's visual field," said Martin. "Such behaviour results in certain species being at least temporarily blind in the direction of travel."Do birds know if you are looking at them? ›
New research demonstrates for the first time that birds also respond to a human's gaze. In humans, the eyes are said to be the 'window to the soul', conveying much about a person's emotions and intentions. New research demonstrates for the first time that birds also respond to a human's gaze.Can my bird tell when I'm sad? ›
Parrots are very sensitive to our emotions, sometimes better than we are. Our birds are keen observers of our facial expressions, body language, tone and even energy levels and therefore we have to be cognizant of how our emotions can impact our birds.Do birds like to be petted? ›
Most birds (unlike other pets) prefer being petted against their feathers. If your bird is getting relaxed and comfortable with you touching them, you can gradually start rubbing the sides of their head gently, including the skin just behind their beak and around their ears (but be careful around the eyes).Do birds remember who you are? ›
Summary: New research suggests that some birds may know who their human friends are, as they are able to recognize people's faces and differentiate between human voices.What do birds sense that humans Cannot? ›
In addition to a sharper visual field, birds are able to detect movement easily and they can fully interpret a very brief sighting. For people, a brief flash of a picture does not give our brain enough time to process and understand what we see. For birds, this is not an issue.
Are birds loyal to humans? ›
Pet birds make great companions. They are full of personality and offer loyal friendship if raised and cared for properly. Some birds are easy to connect with right off the bat, while others may take some time to warm up.