Hummingbirds see more colours than us

A hummingbird that lives on flower nectar does not have a great sense of smell. Besides, except for hermit hummingbirds, most do not sing to attract females or scare off rivals. So how does this tiny bird feed on prey, find partners and stay safe from predators?

Like its mesmerising colourful feathers, hummingbirds rely mostly on colours. According to the research "Wild hummingbirds discriminate nonspectral colours", it turns out that we humans miss the full of the world of colours as hummingbirds can detect more colours than us.

A journal named Proceedings of the National Academy of Sciences published the finding on June 15, 2020.

Like most of the other primates, we humans are trichromatic. It means our eyes only have three types of colour-sensitive receptors or cones: blue, green, and red. But the birds are tetrachromatic. It means they have four types of cones.

As a result, their colour-combination possibilities are multiplied in comparison to humans' ability to see the colours of the rainbow; the spectral hues and one pure nonspetral colour – purple.

The study was conducted with broad-tailed hummingbirds – scientifically known as Selasphorus platycercus – and the study revealed that the fourth cone of the birds can detect Ultraviolet(UV) lights making their world more colourful.

For the study, the research team set up several-tube bird feeders outfitted with LED devices near the Rocky Mountain Biological Laboratory in Colorado. They used sugar solution as a reward and programmed LED devices near the feeders to turn a surface two different colours.

The hummingbirds quickly identified the associated colour that had a rewarding sweet sip and the other associated with plain water.

The scientists, from 2016 to 2018, conducted 19 experiments and tracked around 6,000 broad-tailed hummingbirds visiting the feeders. They showed that the broad-tailed hummingbirds – regardless of the spectral or nonspectral hue – consistently chose the feeder with a sweet taste though the colours seemed almost the same in the naked human eyes.

Combining the spectral light with UV, the researchers proved that when the birds look at objects, they can certainly see many more colours because of that fourth cone whereas we human can see only the spectral lights.

To determine why hummingbirds see such a variety of colours, the researchers also analysed the existing data of various bird plumage colours and plant colours. This part of the research revealed that 30 percent of the birds' plumage and 35 percent of the plant colours are in nonspectral hues that hummingbirds can identify.

These are the colours we humans cannot even imagine.

When we look at a yellow flower, we see only a yellow blossom. Who knows what it would be like to see the same flower with the hummingbird's eyes and submerge into the world of colours!