The first question would be: The colors we can see are they all there? Humans have tricolor cones on the retina. They are sensitive to red, green and blue light. But not the birds. They have a fourth colored cone that can capture ultraviolet light. A team from Princeton University (USA) examined wild hummingbirds. They carried out a series of color experiments. The results show that hummingbirds see more colors than we do.
The results were published in the journal ‘Proceedings of the National Academy of Sciences’. “Humans are color blind compared to birds,” he says. It is a statement Mary Caswell Stoddard. She is a professor at Princeton University.
“A fourth color cone type extends the color range that birds can see in UV rays. You perceive combined colors such as ultraviolet + green and ultraviolet + red. “
The team trained the broad-tailed hummingbirds (‘Selasphorus platycercus’) to take part in experiments. “Hummingbirds are perfect for studying color vision in nature,” says Stoddard. They react to the colors of the flowers, which announce a reward with nectar ».
They founded two feeders: one with sugar water and one with running water. They placed an LED tube next to each feeder. The tube next to the sugar water emitted a color (each different).
The researchers regularly exchanged the positions of the satisfactory and unsatisfactory tubes. Within a few hours, wild hummingbirds learned to visit pleasant colors. In a series of 19 experiments, they recorded more than 6,000 feeding visits.
Experiments have shown that hummingbirds can see a variety of non-spectral colors. For example, hummingbirds can easily distinguish ultraviolet + green from pure ultraviolet or pure green. They differentiated between two different mixtures of ultraviolet + red light: one more red and the other less.
Hummingbirds continued to correctly choose the ultraviolet + green light associated with sugar water. A human would see the identical colors. But it is impossible to really know how birds perceive these colors. Is ultraviolet + red a mixture of these colors or a completely new color? You can only speculate.
The wide variety of non-spectral colors available to birds is the result of the old visual system with four color cones.
“Tetrachromy with four types of color cones developed in the first vertebrates,” says Stoddard. This color vision system is the norm for birds, many fish and reptiles. It almost certainly existed with dinosaurs. Hummingbirds not only see more colors than we do, but also many animals.