How Do Hummingbirds See Flower Colors in Ultraviolet?
As an Amazon Associate we earn from qualifying purchases.
How do hummingbirds see flower colors in ultraviolet? The short answer is a fourth color cone in the eye that responds to ultraviolet light. Birds have four color cone types, compared with three in humans, and that extra cone widens the range of colors they can tell apart. This article explains how the cones and their oil droplets work, what experiments show about hummingbird color discrimination, and where the evidence stops.
Quick answer
- Hummingbirds have a UV-sensitive cone whose peak sensitivity sits in the ultraviolet range, roughly 360 to 370 nanometers in the model the source describes.
- Oil droplets inside the cones act as filters, and the UV cone has a transparent droplet with no carotenoid.
- Wild broad-tailed hummingbirds can tell apart colors that combine ultraviolet with red, green, or yellow, which is a stronger test than simple color matching.
Why hummingbirds have a fourth color cone
Most animals with color vision rely on several types of photoreceptor cells, called cones. The source explains that “Birds, by contrast, possess a fourth color cone type, which is sensitive to UV wavelengths.” Humans have three cone types, so birds can represent colors in a space with an extra dimension.
The number of cone types is only part of the picture. The first source makes the point that “it is not the number of photoreceptor types but how they interact that determines the dimensionality of an animal’s color vision.” In other words, a bird’s color perception depends on how its cones combine signals, not just on how many cones it has.
Hummingbirds are the focus of this question. The second source states that “Hummingbirds are believed to possess the VS-type visual system; their predicted color cone sensitivities are shown” in its figure. The VS label refers to a violet-sensitive cone, and the source notes that “For simplicity, we refer to colors that would stimulate the UVS or VS cones as ultraviolet.”
How the UV cone and oil droplets work
The first source describes the cone system in detail. It says that “A special trait of bird’s cones is the presence of oil-droplets” which are “spherical lipid structures inserted in the inner segment of the photoreceptor.” The droplets act as filters, and their optical properties “depend on carotenoid contents and concentrations.”
The UV cone is the one that matters for this question. The source explains that “The V-cone or UV-cone contain a transparent (t) oil-droplet with no carotenoid.” A transparent droplet lets ultraviolet light reach the visual pigment without the colored filtering that the other cones receive.
The source gives a numeric range for the UV cone’s peak sensitivity. It lists the “ultraviolet-sensitive-cone (UV-cone) with λmax (between 360 nm and 370nm )” as one of the cone types found in birds. Those figures describe the cone’s peak light absorption, and the source uses them as inputs to its model.
The model combines these properties to predict what the eye sees. The source describes how “The final cone mechanism sensitivity is then determined by combining the cone visual pigment absorption and oil-droplet transmittance.” That combined sensitivity is what the researchers compared against electroretinogram results, which measure the electrical response of the retina to light.
Why ultraviolet matters to birds
Ultraviolet is not just a physical curiosity for birds. The first source says that “In many birds, ultraviolet (UV) is a color that is believed to be involved in social communication, food or sexual selection.” That is the broader context for why a plant’s ultraviolet signals might matter to a hummingbird.
Hummingbirds specifically learn to link colors with food. The first source states that “It has been well established that hummingbirds learn to associate the rich nectar contents of flowers with different colors, varying from red to ultraviolet.” This is the connection between the eye and the flower: the bird learns which colors signal a reward.
What experiments show about nonspectral color
A basic question is whether a hummingbird can tell apart colors that no single wavelength of light can match. The second source explains the concept: “Nonspectral colors are perceived when nonadjacent cone types (sensitive to widely separated parts of the light spectrum) are predominantly stimulated.” Purple is the familiar human example, because it stimulates the blue and red cones together.
Birds with four cone types can, in theory, see many more of these colors. The source says that “In theory, this enables birds to discriminate a broad range of colors, including many nonspectral colors.” The same source states that “Except in primates and bees, few behavioral experiments have directly examined nonspectral color perception,” which is why the hummingbird test is significant.
The field test used wild birds. The source describes how “we trained wild hummingbirds to participate in color vision tests.” The result was that “They can discriminate a variety of nonspectral colors, including UV+red, UV+green, purple, and UV+yellow.” The study reports that the population value across nonspectral experiments was “0.83,” with “posterior support for a mean discrimination >0.75.”
The authors also looked at natural colors. The second source reports that “based on an analysis of ∼3,300 plumage and plant colors, we estimate that birds perceive many natural colors as nonspectral.” This matters for flowers, because it suggests that many of the colors a hummingbird sees in nature fall outside the simple spectral range.
How we chose these sources
Both sources are hosted on the NCBI PubMed Central site, and neither is a retail page. One paper is a modeling study that uses electroretinogram data from firecrown hummingbirds. The other is a field study of wild broad-tailed hummingbirds that tests nonspectral color discrimination. Together they cover the eye’s physical hardware and the bird’s behavior, which the question needs.
Each source was fetched directly and returned HTTP 200 on the date of checking. Quotes were copied from the fetched text, and the explanation above rests on those quotes as listed in the sources file.
For readers who want to attract hummingbirds to their own yard, the guides on attracting hummingbirds to your yard and attracting hummingbirds without a feeder cover the garden side of the topic.
What we could not verify
What the sources do not say
The modeling study is based on electroretinogram data from firecrown hummingbirds, and the field study is based on broad-tailed hummingbirds. Neither source tests a flower in the wild and reports which flower colors a bird prefers, so the explanation above does not say which garden flowers look most attractive under ultraviolet light.
The sources also do not describe how far ultraviolet signals reach across a garden, or how a flower’s ultraviolet pattern compares with its visible color for every species. The article treats the sources’ numbers as the values reported in those papers and does not extend them to other birds or insects.
Frequently asked questions
Can hummingbirds see ultraviolet light?
The sources describe a UV-sensitive cone in hummingbird-type eyes. The first source states that “ultraviolet-sensitive-cone (UV-cone)” has a peak sensitivity between 360 nm and 370 nm, and the second source says that hummingbirds “are believed to possess the VS-type visual system.”
Why do birds need four cone types instead of three?
The second source says “Birds, by contrast, possess a fourth color cone type, which is sensitive to UV wavelengths.” It also notes that “In theory, this enables birds to discriminate a broad range of colors, including many nonspectral colors.”
What are oil droplets in a bird’s eye?
The first source describes them as “spherical lipid structures inserted in the inner segment of the photoreceptor.” They “form long pass filters with optical properties that depend on carotenoid contents and concentrations.”
Do hummingbirds see flowers differently from humans?
The sources suggest they can. Humans have “three primaries” for matching color, while birds have four cone types. The field study found that hummingbirds can discriminate colors such as UV+red and UV+green, which the source describes as nonspectral.
Can a gardener use this information to pick flowers?
Not directly. The sources study the eye and behavior in controlled or field tests. They do not rank garden flowers, so the information explains the mechanism rather than giving a planting list.
Sources
- “Do Hummingbirds See in Ultraviolet?” PubMed Central, https://pmc.ncbi.nlm.nih.gov/articles/PMC2705111/
- “Wild hummingbirds discriminate nonspectral colors.” PubMed Central, https://pmc.ncbi.nlm.nih.gov/articles/PMC7334476/
