By Regina Rodeghiero
Can you imagine being surrounded by vividly vibrant colors and unusual patterns on various birds flying about you? This is an everyday sight for birds, but as for humans, the sight is otherworldly and unimaginable. How do bird’s eyes and human’s eyes differ? When birds look at each other, they see an astonishing amount of pigments and patterns that adorn each birds’ feathers and beak, a sight that is inconceivable for the human mind. How is this possible?
Birds can see ultraviolet or UV light. It exists because humans see wavelengths between 390 nanometers and 700 nanometers; this ranges from violet to red and is called the visible spectrum. Humans have trichromatic vision and therefore detect light with three kinds of retinal cone photoreceptors. The retina where these are located contains about 130 million photoreceptors that change rays of light into electrical impulses that travel to the brain. Birds differ in that they contain more photoreceptors than humans and have four kinds of retinal cones instead of three. Bird’s eyes also use a retinal oil that contains pigments to protect its eye from the damage of ultraviolet light and filter out the extraneous wavelengths. Lastly, birds have a double retinal cone whose purpose is currently unknown.
Birds are divided into two groups based on the color of light (wavelength) that their retinal cones detect most intensely. Scientists define the two groups as ultraviolet-sensitive or as violet-sensitive. These patterns and pigments help birds tell each other apart. For example, a male and female parrot that look indistinguishable to us may have UV patterns that make them appear diverse to each other. Birds also rely on their perception of UV light for success and survival. These fluorescent pigments play a significant role throughout an avian species’ life in selecting mates, differentiating eggs, healthy fledglings, and foraging for food.
Ultraviolet light and fluorescence constitute a significant factor in natural selection between male and female birds. To illustrate; depending on the species, a female might choose a male with more or less fluorescence that determines how healthy the male is and therefore, will produce healthier offspring. Next, the eggs have specific patterns that distinguish a mother’s eggs from those of a different species. A mother bird does not want to feed unwell hatchlings when the same resources could be feeding the healthy and likely-to-survive young. Therefore, the pigments and patterns on chicks tell the mother bird whom to feed while marks on their beaks tell her where to put the worms. Fowls use UV light to their advantage when foraging for food as berries reflect light, and for raptors as vole’s urine trails reflect light, possibly even leading to its next meal.
Birds have such a larger sense of color then us humans do, and as for food, they are able to sustain themselves thanks to this highly-sophisticated ability. A bird’s ability to see ultraviolet light is a vital part of their survival, and without it they might have become extinct. Scientists are studying this ability because it could lead to many technological advances in the future and a more comprehensive understanding about our world, for both our feathered friends and humanity itself.