We often think that animals see the world the same way we do, but this is not true. Many animals have different fields of vision due to the placement of their eyes, and others see different spectrums of light than we do.
Birds see in colour and see more of the colour spectrum than humans and other mammals. Birds have a fourth cone in their eyes which allows them to see ultraviolet light. UV light enables them to hunt more effectively for insects and fruit, helps them find a mate, allowing them to navigate better.
Bird vision is the most highly developed and acute sense among birds, and a large part of this is their keen sense of colour. Understanding how birds see can help us understand more about their behaviour.
What colours do birds see?
Birds see different colours than humans. Humans can see red, blue, and green and combinations of these. Birds can see the familiar rainbow of colours we know and parts of the ultraviolet (UV) spectrum that we can’t see.
Bird vision is also sharper than humans. Birds can distinguish slight differences between similar shades, so they can see colours that we can’t.
Cones in the eye give animals colour vision. Birds generally have four cones in their eyes instead of three like humans, and they perceive colour differently. Not all birds have four cones, but birds typically have more cones than humans and other mammals in their retinas.
Each cone in the retina has a drop of oil in it. This oil filters out different colours, allowing the birds to see different shades, much like a camera filter. The oil is either transparent, pale, red, or yellow and contrasts between colours. The oil helps birds filter out leaves, bushes, and trees to find their prey and can even help them find fish in deep water. Mammals, including ourselves, do not have oil in their eyes.
Eagles see through a yellow filter from the oil. The yellow allows them to see subtle and slight shifts in their vision, such as a vole in the distance, allowing eagles to see their outlines clearer.
Humans can see one nonspectral colour, purple. We can see purple when our blue and red cones are stimulated. Scientists believe that birds can see up to five: purple, ultraviolet and purple, ultraviolet and green, ultraviolet and red, and ultraviolet and yellow.
Using a series of experiments, scientists found that hummingbirds can recognize a variety of nonspectral colours. These include purple, ultraviolet and green, ultraviolet and red, and ultraviolet and yellow.
Birds with the best colour sense are birds that are active during the day. Diurnal birds need to filter out more colours than nocturnal birds.
As with other nocturnal mammals, nocturnal birds can see better at night due to having more rods in their eyes. Rods do not help them see colour, but they do help to see better in low light.
Unlike humans, birds can see ultraviolet light spectrums. Seeing in UV allows birds a different perception of the world and helps them survive in the wild.
How colour helps birds find food
Many birds survive on a diet of fruits and berries, and their ultraviolet eyesight helps them. Seeing in the ultraviolet allows birds to see some berries and fruits much clearer against bushes and trees as the fruit reflects UV light.
Birds see more shades than humans, with leaves appearing darker underneath and lighter on top. This is why you often see some birds land on a fruit bush and immediately start eating the fruit.
Colour vision can also stop them from eating poisonous plants. Many toxic plants are brightly coloured, which birds can spot quickly and easily.
Hummingbirds feed on the nectar from flowers, and there is evidence that seeing ultraviolet colours aids them in finding flowers with the most nectar.
Although many small mammals will try to hide in bushes or under stones when they spot a predator such as an eagle, they don’t realize predators can see their trails and urine in the ultraviolet spectrum.
How colours help find a mate
Male and female birds of many species look similar when viewed by ourselves, but the ultraviolet spectrum shows differences in their feathers and plumage. Because birds can see in ultraviolet, they can immediately tell the males from females allowing them to find a mate easily.
Ultraviolet helps birds navigate
The sun is probably the best-known source of ultraviolet rays. Although we cannot see the ultraviolet light, we do feel the effect of it. Ultraviolet light can penetrate thin cloud cover. This allows birds to find the position of the sun, which helps them in navigating.
Choosing their own eggs
For years, ornithologists and scientists could not work out how birds can tell their eggs from other birds’ eggs, but this comes down to their extended vision. Patterns that show up only in ultraviolet allow the parents to find the correct eggs when many others are nearby.
Knowing when to migrate
Although not the only reason for knowing when to migrate, the colour of the foliage helps the birds know that the seasons are changing and that it will soon be time to move to a warmer climate.
Birds can see in colour and different spectrums to ourselves. As we can see, it helps them survive in many ways. Their colour vision helps them find a mate, see which eggs are theirs, and find food, while also helping them navigate.