Seeing colour
How animals see colour
Dogs see two colour channels, people three, birds four. Bees see ultraviolet. More receptors do not always mean better colour.
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Animals see colour very differently from people and from each other. It depends on how many kinds of receptor they have and which wavelengths those respond to. Most mammals have two kinds. Humans and many other primates have three. Birds, reptiles and many fish have four. Bees see ultraviolet light but not red. Each system suits the life the animal leads.
Mammals
Dogs, cats, cattle and horses have two cone types. They see blues and yellows and cannot separate red from green, much like a person with red-green colour blindness. A dog can see a toy on grass less well by colour if the toy is red than if it is blue. Bulls are not angered by red. They respond to the movement of the cape. Whales and seals have only one cone type and probably no colour vision. Among primates, the third cone is thought to have helped in finding ripe fruit and tender young leaves among green foliage.
Birds, bees and fish
Most birds have four cone types, one of them tuned to violet or ultraviolet. Feathers that look plain to us can carry ultraviolet patterns that birds use in choosing mates. Honeybees have three receptor types, shifted towards short wavelengths: ultraviolet, blue and green. The Austrian zoologist Karl von Frisch showed in the 1910s that bees can be trained to find a coloured card. Many flowers have ultraviolet marks that guide bees to the nectar. Goldfish and many reef fish have four cone types, and some deep-sea fish have unusually many light-sensing pigments.
The mantis shrimp
Mantis shrimps, which live on tropical reefs, have twelve or more kinds of colour receptor, and popular articles often claim they see colours beyond imagining. Experiments suggest otherwise. A study published in 2014 by a team in Queensland, Australia, found the animals were worse than people at telling close colours apart. They seem to use their receptors differently, recognising colours quickly by which receptor fires instead of comparing signals. The number of receptor types sets what an animal could see. What it actually sees depends on what its nervous system does with them.
Sources and further reading
- Evolution of color vision on Wikipedia
- Natural History Museum, London: How do other animals see the world?
- Streets and others, Colour vision in stomatopod crustaceans: more questions than answers, Journal of Experimental Biology (2022)
- Scientific American: What Birds See
Original text by the Rang desk, written with AI assistance and checked against the sources above. Meanings of colour vary from place to place and person to person. If we have something wrong, tell us.