Can Birds See Colour?

Birds not only see colours, but they can see far more colours than are visible with the human eye. Birds’ eyes are sensitive to the ultraviolet range, not only that, but they are still evolving within their eyes to see even more colours according to experts at the University of Cambridge and Yale who are doing a joint study on the avian visual system.

The Evolution Of Plumage

Scientists have discovered that over many millions of years of evolution, birds’ plumage changed from dull, drab colours, to bright, exciting colours as the birds gained the ability to make new pigments and colours. Just as our clothes started off dull and drab before the introduction of aniline dyes, but all of a sudden, colours became much cheaper, and so clothes designs evolved into the myriad of colours we see today. According to Richard Prum, one of the research scientists involved in the study, that’s exactly what’s happened with the birds too.

Bird’s Retinas Are Responsible For Their Colour Perception

Scientists have been wondering for years how and why birds got their colours, but this joint project between Cambridge and Yale is the first to ask what all these colours look like to the birds themselves. They discovered that not only can birds see plenty more colours than we can, but also they’re capable of seeing countless more colours than they currently have in their plumage.

It’s all to do with the physical make-up of bird’s retinas, they have more colour cones than human beings. We have 3 cones which basically detect the primary colours-Red, Green and Blue light frequencies. Birds have those same 3 cones plus they have an extra cone, which gives them access to much more colour than we can even imagine. And what’s more, the other frequency that birds can detect varies from species to species.

For example, some birds like parrots have a cone that is able to detect deep into the ultraviolet spectrum. Whereas the Australian honeyeaters 4th cone is sensitive to violet light. 

What Does This Extra Cone Mean In Terms Of Vision?

The easiest way to describe the effect of having a greater sensitivity to UV light is by looking at what humans see when we look at a dense forest. When looking at a particular area of that dense forest, all we can see is basically just a mass of greenery. But the same image under UV, shows the clear image of leaves, this is due to the way the eye processes the image. Birds can distinguish between this green light to detect not only the leaves, but also any insects or other potential food source hiding in those leaves.

“The startling thing to realize is that although the colors of birds look so incredibly diverse and beautiful to us, we are color blind compared to birds.”-Richard Prum (Scientist)

How Do Birds Access Wider Colour Bands Than Humans?

We  have just heard how birds have one extra cone to us and that allows them to access u/v light which gives them access to a greater number of colours than we have. These cells, or cones as they’re called are found in the retina in both us and the birds (and every other creature on earth that possess functioning eyes), but the cones in birds eyes are not only in greater numbers, they also have an extra function.

The Secret Is Cone Oil

Each cone in a bird’s eye has a small droplet of coloured oil,these droplets of oil vary in colour from yellow, red, or a clear pale colour. These oil droplets are not unique to birds, they are also found in the cones of  fish, reptiles and some amphibians,but not mammals. The differences of colour in the oil is due to the concentration of carotenoid pigments which are commonly found in many fruits and vegetables.

What Do These Pigments Do To Affect Colour Detection?

The oil in the cones act like a super powered microlens, light passes through the oil before it gets to the pigment, this allows the pigments to act like filters, which allows the birds to see greater numbers of colours. The pigments remove certain wavelengths which expands the amount of colours the birds can see. They can see shades of colour and discern subtle changes in colour, minute differences that we cannot see.

Night Vision Goggles

It turns out that most of the bird world have this extra cone, which allows them to have both violet sensitivity and ultraviolet sensitivity well the diurnal birds anyway, it’s not so important for nocturnal birds to determine colours so much. However it has been discovered that birds that are active at night have more rod cells in their eyes. Rod cells allow them to see better in low light conditions as they can receive more light due to the rod cells. These rod cells are usually found around the edges of the retina and increase peripheral vision – Very handy if you’re a bird hunting for food at night.

How Does Violet And Ultraviolet Sensitivity Help Diurnal Birds?

Hunting aside, having this increased and improved colour vision and violet and Ultraviolet sensitivity allows birds to recognise many things that are invisible to the human eye. For instance, many bird species that appear to be virtually identical to us when it comes to sexing the birds, have ultraviolet patches on their feathers that allow the birds to differentiate between male and female.

Some Examples Of U/V Recognition In Diurnal Birds

There are many examples of how having extra visual capabilities can assist diurnal (daylight active) birds. Here are a few:

• Female blackbirds are attracted to male blackbirds who have better U/V reflectiveness.
• Male blackbirds when competing with another male over territory are influenced by the degree of orange visible on the bill.
• Male bluetits attract females by displaying their U/V reflective crown patch which becomes visible during courtship.
• Birds of prey use their heightened U/V vision to detect mice, voles and other potential food sources through their urine trails and splashes that these small mammals use to mark out their territories.
• Using their U/V vision birds are able to spot berries virtually completely surrounded by greenery.
• Certain fruits and some berries are coated in a waxy film that reflect U/V light making them easier to detect.
• Various insects, seeds and flowers also reflect U/V light making them easy for birds to detect.
• Seabirds are able to see deeper into the water allowing them easier access to fish.

How Have These Discoveries Assisted The Amateur Birdwatcher?

By using the information collected by the university’s studies concerning their colour and U/V sensitivity various bird friendly products have been developed.  These include:

• The design of cat collars that reflect U/V light to make them easier to see by the birds.
• Preventing birds from flying into windows and glass doors by adding U/V reflective images to window stickers.
• Adding U/V patterns to bird feeders and tables to attract the birds to new feeding stations in a shorter time than usual.
• Coating clothing and field bags with non-reflective coatings which allows birdwatchers to get closer to birds without spooking them.

Egg Rejection

Many songbirds are often tricked into rearing the chicks of cuckoos that have hatched in the songbirds nest with their own eggs. Some songbirds reject these “alien” eggs even though they look identical to the human eye. But under U/V lighting, they are completely different, with the recent discoveries concerning bird U/V sensitivity it’s easy to understand how they were discovered. But some songbirds do accept these cuckoo eggs, are they just generous, or do they lack the U/V sensitivity? That’s for future research we suppose.

Feeding Hatchlings Using U/V Sensitivity

A Spanish study conducted on the European Roller, a colourful bird (even to human eyes), found that newborn hatchlings have a bald patch on their foreheads. This patch reflects U/V light at different levels depending on how hungry they are. Scientists applied sun blocker on the forehead of some chicks and a control lotion on the rest, the ones with the sun blocker were decidedly thinner at the end of the experiment than their unblocked nest neighbours. Which proves that it’s the U/V signals that determine who gets fed.

4 Cones Are Not Always Better Than 3

Scientists have concluded that the extra cone in the retina that gives birds their incredible sensitivity to violet and ultraviolet light does have one drawback. Having a fourth cone class in the retina takes up space that could have been used by the other 3 classes. This can lead to less resolution on normal images and also less vision when lighting is dim.

Pigeon Power

It has been known for some time that birds have superior vision, in 1979 the US coast guard used 3 pigeons to search for 5 missing fishermen. They were suspended in a cage underneath a helicopter, when they spotted any coloured debris floating on the water they pecked at a button in the cage. If 2 of the birds pecked on the switch, a light would flash in the helicopter alerting the human team who would search in a more focused fashion on that particular area.

The results of these experiments were that the pigeons had a success rate of 90% which was 50% more times than the human searchers. These experiments were eventually phased out due to greater success using dolphins who had the advantage of being actually in the water.

Are Birds Attracted To Particular Colours (That We Can See)?

U/V sensitivity aside, are there any colours in our spectral range that birds are attracted to? The answer is yes, some birds seem to be attracted to yellow and red. For instance hummingbirds are attracted to red flowers, which explains why almost all hummingbird feeders are red, or at least have a part that is red.

If you want to attract birds to your garden, be sparing with the white paint. Apparently, birds see white as a colour of warning.

Why Most Bird Sexes Look The Same

Have you ever wondered why 92% of all diurnal birds look the same in both sexes? Well, they don’t, at least not in their eyes. Thanks to those fourth cones in their retinas, all of the differences in the sexes of birds are invisible to the human eye. 

There is much more study needed to understand more fully how birds see colours. But with each new discovery birdwatchers and ornithologists can increase their knowledge to learn more about birds and understand their behaviour more fully.

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