Hummingbirds have excellent color vision that allows them to see colors that humans cannot. Their ability to see a wide range of colors aids them in finding food sources and selecting mates. In this article, we’ll explore what is known about hummingbird color vision, the colors they see best, and how their visual system is adapted to their needs.
Hummingbirds are known for their iridescent plumage and preference for red tubular flowers. Their excellent color vision and ability to see ultraviolet light gives them an advantage when foraging. Humans have three types of color receptors (cones) in our eyes that allow us to see the colors red, green, and blue. Hummingbirds, on the other hand, have four cones that let them see red, green, blue, and ultraviolet. This gives them an expanded color spectrum compared to humans. The range of wavelengths a species can detect is determined by the visual pigments present in their cone cells. By studying the DNA sequence of visual pigment genes, scientists can determine what colors an animal is likely able to see. This technique has revealed that hummingbird vision is finely tuned to seeing both red flowers and ultraviolet “nectar guides” on petals. Their visual system plays an essential role in their lives, from finding food to selecting mates and avoiding predators.
Hummingbird Vision and Color Perception
Hummingbirds have the most diverse color vision of any land vertebrate. They have four types of cone cells with visual pigments that are sensitive to violet, blue, green, and red light. Having an extra cone type allows them to see into the ultraviolet spectrum, which humans cannot detect. The four cone types are stimulated by light at the following peak wavelengths:
| Cone type | Peak sensitivity |
|---|---|
| Violet | 415 nm |
| Blue | 455 nm |
| Green | 508 nm |
| Red | 565 nm |
Having an ultraviolet-sensitive cone allows hummingbirds to see nectar guides on flowers that guide them to the nectar. These guides reflect UV light and often form patterns like lines, dots, and rings that are visible only to animals that can see UV, like hummingbirds and bees. This helps the birds quickly identify flower species with their preferred nectar.
The hummingbird’s visual system is well-adapted to their needs. Their eyes have more cones relative to rods compared to other birds, giving them better color vision. They also have a large neuroendocrine structure called the parvocellularis, which processes input from the red-sensitive cone. This allows them to perceive the color red intensely, which aids in finding food sources. Many of the tubular flowers that hummingbirds pollinate reflect long-wavelength light and appear intensely red to the birds. While humans see wavelengths up to around 700 nm, hummingbirds can detect light up to around 800 nm, letting them distinguish colors we cannot see.
Preferred Flower Colors
Hummingbirds visit flowers across the visible color spectrum, but they do seem to have preferences when given options. Researchers have conducted experiments with dyed sugar water and artificial flowers to test hummingbird color preferences. Several studies have shown that hummingbirds are highly attracted to red and orange flowers. One reason is that these flowers stand out amongst green foliage, making them easier to spot. Red also signals that a flower contains abundant, energy-rich nectar.
Multiple studies have shown the following color preferences in hummingbirds:
| Color | Preference Level |
|---|---|
| Red | High |
| Orange | High |
| Yellow | Moderate |
| Green | Low |
| Blue | Low |
| Violet | Low |
Though not their top choice, hummingbirds readily feed from flowers of many colors. Native plants that have coevolved with local hummingbirds produce flowers in colors preferred by their pollinators. Introduced garden flowers are often bred to have a red coloration attractive to hummingbirds.
How Hummingbirds Use Color Vision
Hummingbirds rely on their exquisite color vision for essential daily tasks:
Finding food: The red color vision helps hummingbirds identify tubular bird-pollinated flowers, an important nectar source. UV sensitivity allows them to see nectar guides on flowers.
Selecting mates: Vibrant, iridescent plumage plays a key role in attracting mates. Females likely use coloration to assess male fitness.
Communication: Throat feathers called gorgets appear particularly colorful to other hummingbirds and are used for signaling.
Predator avoidance: Color vision helps hummingbirds quickly identify food sources while avoiding mimicry by predators like orchid mantises that have adapted to exploit hummingbird vision and behavior.
Experiments that altered flower colors showed hummingbirds had difficulty finding food, confirming they rely strongly on color cues. Their behavior and physiology are tuned to take advantage of the extensive color information available to them. Hummingbird species with especially vivid plumage are those that live in dense tropical environments where color vision for communication is particularly beneficial. The reliance on color vision has shaped hummingbird evolution and anatomy over millions of years.
Differences Between Hummingbird Species
There are over 300 species of hummingbirds that display subtle differences in their color vision. For example, the ruby-throated hummingbird has three types of oil droplets (organelles that filter light) associated with its cone cells: red, orange, and clear. Meanwhile, the Anna’s hummingbird has four types: red, orange, yellow, and clear. This allows the Anna’s hummingbird to distinguish even more shades of color. The black jacobin hummingbird can see UV light down to ~370 nm, into the near UV spectrum.
Some key differences:
| Species | Total cones | Oil droplet types | UV range |
|---|---|---|---|
| Ruby-throated | 4 | Red, orange, clear | 400 nm |
| Anna’s | 4 | Red, orange, yellow, clear | 400 nm |
| Black jacobin | 4 | Red, yellow, clear | 370 nm |
Subtle tuning of visual systems for specific habitats and resources occurs between different hummingbird species. Those that pollinate a wider variety of flower species tend to have more advanced color discrimination abilities.
Conclusion
In summary, hummingbirds see a wide range of colors thanks to having four types of cone cells. This allows them to see into the ultraviolet spectrum. Of colors hummingbirds can detect, they are highly attracted to red and orange flowers, followed by yellow. Red flowers stand out against green foliage, making them easier to find. The multiple adaptations in the hummingbird visual system allow them to make use of the extensive color information available. Variations in their visual perception exist between the many species of hummingbirds, with their vision fine-tuned to their ecological niches.
