Many people assume that animals only see in black and white. However, the truth is that many animals have color vision, but how they perceive color varies widely between species. There are a few key factors that determine whether an animal can see color or only shades of gray.
The basics of animal color vision
In humans and many other species, color vision relies on specialized photoreceptor cells in the retina called cones. There are three types of cones that are each sensitive to different wavelengths of light. The specific colors they detect are blue, green, and red.
The presence and number of these cone cell types allows different species to have different types of color vision:
- Monochromats only have a single cone type and can only see shades of gray.
- Dichromats have two cone types and can distinguish some colors.
- Trichromats have three cone types and full color vision.
The more types of cones available, the more colors an animal can distinguish. However, it is not just the number of cones that matters, but also how the information from the different cones is processed by the brain.
Monochromatic vision
Many marine mammals such as whales and dolphins are monochromats, meaning they only have a single cone cell type in the retina. This means they can only perceive differences in brightness and see in shades of gray rather than full color vision. Their vision is adapted to function well in the ocean where color signals are less useful.
Other animals like cats and dogs only have two cone types and are also thought to be functionally monochromatic. However, there is some debate about whether they may have limited color discrimination abilities.
Dichromatic vision
Many mammals are dichromats, meaning they have two types of cone cells and can perceive some color hues. However, with only two cone cell types, they cannot distinguish as many colors as trichromats.
Examples of dichromatic mammals include:
- Horses
- Rabbits
- Gorillas
- Dogs
- Cats
With two cone types, dichromats can match any color they see into red and blue-green categories. They have trouble distinguishing colors that trichromats find very distinct, like red vs orange or green vs blue.
Trichromatic vision
Primates, including humans, are trichromatic. This means they have three cone cell types allowing full color vision. The three cones are specialized to detect blue, green, and red light.
Many birds are also trichromatic, along with reptiles and amphibians. Insects like bees can even be tetrachromats with four color receptor types extending into the ultraviolet range.
Some key examples of trichromatic animals include:
- Humans
- Apes
- Monkeys
- Lizards
- Turtles
- Frogs
- Birds
- Fish
- Insects
With three cone cell types covering different color ranges, trichromatic animals can distinguish many more colors than dichromats, especially in the red-orange-yellow and green-blue ranges.
Differences in animal color vision
While the number of cone cell types defines mammals as monochromats, dichromats, or trichromats, there are many other factors that influence how color is perceived between species.
Some key differences include:
- Number of cones – More cones dedicated to a certain color range enhances discrimination in that color.
- Distribution of cones – The area on the retina covered by certain cones affects visual acuity for those colors.
- Overlap between cones – The degree of overlap in sensitivity between cone types changes color distinctions.
- Neural processing – The way signals from cones are interpreted by the brain shapes perceived color.
This means that even trichromatic animals likely perceive color somewhat differently than humans. We can get some idea of these differences by looking at the visual pigments that respond to light in animal eyes.
| Animal | Cone Types |
|---|---|
| Humans | Blue, Green, Red |
| Monkeys | Blue, Green, Red |
| Mice | Ultraviolet, Blue, Green |
| Birds | Ultraviolet/Violet, Blue, Green/Red |
| Dogs | Blue/Violet, Green/Yellow |
As the table shows, even though mice and birds are trichromatic like primates, the cone cell types are shifted towards ultraviolet and violet detection compared to humans. This means they can likely perceive colors in the UV spectrum that humans cannot.
Color vision in specific animals
Dogs
For a long time dogs were thought to be completely colorblind, but recent studies suggest they have dichromatic color vision similar to other carnivores. They only have two types of cone cells and appear to see blues, grays, and yellows best.
Behavior tests show that dogs can distinguish blue or yellow objects from gray, but have difficulty with red or green. So while not completely colorblind, dog color vision is much more limited compared to humans.
Cats
Cats are also dichromats with cones sensitive to blue-violet and green-yellow light. But cat color perception may be even more restricted than dogs. Research suggests they struggle to discriminate colors other than high contrast blues and yellows.
Cats do have a much higher density of rods compared to cones. This makes their vision optimized for night-time environments where color vision isn’t very useful.
Horses
Horses have dichromatic vision very similar to dogs and cats. They have blue and green/red cone cells but lack a dedicated red cone. This means they can distinguish blue and yellow, but reds, greens, and oranges likely appear more similar.
However, horse vision is quite blurry for stationary objects. Their color perception seems to be optimized for detecting motion rather than identifying colored objects or patterns.
Birds
Most diurnal birds, like parrots, songbirds, and falcons, are trichromatic with four cone types: violet, blue, green, and red. Some owls and other nocturnal species are dichromats as color vision is less critical in low light.
Birds can not only see more colors than mammals overall, but their vision extends into the ultraviolet range that is invisible to humans. Many birds use UV signals for communicating that they can detect but we cannot.
Reptiles and amphibians
Most reptiles and amphibians studied, like turtles and frogs, have been shown to have trichromatic vision similar to birds. In addition to blue, green, and red cones, they also have cones sensitive to ultraviolet and violet light.
This gives amphibians and reptiles an even greater range of color perception compared to humans. It likely aids in tasks like mating displays, detecting camouflage, finding food, and communicating using bright color patterns.
Fish
Research shows that most fish species have trichromatic or possibly tetrachromatic vision. Along with blue, green, and red sensitive cones, some fish also have a fourth cone type detecting ultraviolet light.
Color vision in fish helps with essential underwater tasks like schooling, selecting mates, detecting prey, and avoiding predators. But different species are adapted to the specific light conditions of their habitats.
For example, rainbow trout have cones tuned for short and medium wavelengths to see better in murky rivers. Cichlids in clear waters rely more on longer red and UV wavelengths for visual communication.
Insects
Insects like bees and butterflies have some of the most complex color vision in the animal kingdom. Most have tetrachromatic vision with four types of photoreceptor cells.
These usually consist of a dedicated ultraviolet receptor along with blue, green, and red receptors. Some species may even have five or more color channels. This gives insects an incredibly vivid view of the world.
Insects use their complex color vision to find food sources, detect camouflaged mates, navigate using the sun, and see a range of visual signals from ultraviolet to infrared.
Differences in color perception
The color categories perceived by an animal depend on the peak sensitivities of its cone cells. Even if two species are trichromatic, the hue ranges they see can be quite different.
Human vision relies on medium wavelength cones peaking at green light. But many birds and reptiles have cones tuned for red light instead. This shifts their perception of orange, yellow, green, and blue hues compared to humans.
Some key examples of differences in color perception include:
- Birds and reptiles can detect ultraviolet wavelengths invisible to humans.
- Mammals lack sensitivity to red light which is a dominant color for birds.
- Dichromats are colorblind to certain hues in the red-green range.
- Fish adapted to murky water may only distinguish blue from red.
- Nocturnal animals favor rods over cones and tend to see only shades of gray.
These differences mean an animal’s subjective experience of color does not map neatly onto human color categories. But we can understand the basics of animal color vision by studying their photoreceptor cells.
Conclusion
While many mammals only see in shades of gray, other animals like birds, fish, and insects enjoy a vibrant, colorful world. The type of color vision depends on the classes of cone photoreceptors present in the eye.
Trichromats with three cone types can see the full spectrum of hues, while dichromats with two cones have limited color perception. But even among trichromats, the specific cone types vary, shaping how different animals perceive color.
Research shows most vertebrates are either di- or trichromatic. Invertebrates like bees exceed human color vision with tetrachromacy. But mammals are unique among animals in favoring luminance over color for most visual tasks.
So while the phrase “colorblind as a dog” has some truth, we now know dogs and other mammals see at least some colors. Yet their perception of rainbow hues is limited compared to many fish, birds, reptiles, and insects.