Ultraviolet (UV) light plays an important role in the lives of many bird species. Birds can see UV light, which is invisible to humans, and use it for various purposes including mate selection, foraging, orientation, and communication. Here we will explore how birds use UV light and the effects it has on them.
Birds Can See UV Light
Many birds have the ability to see UV light thanks to special pigments in their eyes that allow them to detect wavelengths between 300-400nm. Humans cannot see UV light because our lenses filter out these shorter wavelengths. For birds, seeing into the UV spectrum provides them with extra visual information about their environment that humans miss out on.
UV Vision Helps Birds Choose Mates
One of the main ways birds utilize their UV vision is to help select mates. Many bird species display UV reflective plumage that is used to attract partners. For example, the crow-like birds called grackles have iridescent feathers that reflect UV light. The amount of UV reflectance indicates the health and condition of male grackles, allowing females to select the most fit partners.
Other bird species like parrots and macaws have areas of UV reflective feathers used for mate communication. This allows the birds to display patterns to each other that are imperceptible to predators. Overall, the ability to see UV reflective feathers allows birds to impart important information to potential mates that humans are unable to detect.
UV Vision Aids Foraging
In addition to mate selection, many birds rely on UV vision to locate food sources. The flowers of many plants display UV absorbent nectar guides that are meant to attract pollinators like bees, butterflies, and hummingbirds. These nectar guides are invisible to humans but appear as bright landing strips to birds that can see UV light. This helps guide pollinating birds right to the nectar they seek.
Fruits also signal their ripeness to birds via UV reflectance. As berries and fruits ripen, the chlorophyll breaks down and UV reflectance increases. Birds can easily spot the bright UV fruits against green foliage, allowing them to efficiently find and consume ripe food.
UV Light Aids Orientation
Seeing UV wavelengths also allows birds to properly orient themselves using clues invisible to humans. One way is by detecting the location of the sun even on cloudy or foggy days by locating UV light scattered through the atmosphere. Birds are able to determine the precise direction of sunlight which aids navigation and orientation when other visual landmarks are obscured.
Birds can also orient by the UV patterns in the sky near sunrise and sunset. The changing gradients of UV light near the horizon provide birds with compass references that are unavailable to humans.
UV Light Plays a Role in Communication
As mentioned before with mate selection, UV reflectance is an important component of visual signals used in bird communication. In addition to decorative plumage, some bird species have UV reflective skin and beaks used for communication. For example, the auklet seabird has a UV reflective beak it uses to signal rank and attract mates.
Many bird songs and calls also contain UV reflectance or illumination that provides extra information to other birds. Kiwi birds create UV light via chemicals in their eggshells to signal incubation status to their mates. Overall, sensitivity to UV light allows birds to gain a great deal of visual information from one another.
UV Exposure Has Health Effects on Birds
While birds can detect and utilize UV light, overexposure has been shown to negatively impact health. UV radiation can damage delicate structures in bird eyes, leading to disorders like pterygium and cataracts. Intense UV exposure is also known to suppress immune function in birds.
In a study of zebra finches, increased exposure to UV radiation decreased hatching success of eggs. This effect was mitigated when UV filters were used to block excess radiation. Thus, although birds have adaptations to prevent damage, intense UV light still poses risks especially when birds are unable to seek proper shelter.
Protective Adaptations Against UV
To help prevent UV damage, birds have evolved a few protective adaptations:
- Special UV filtering pigments in the eyes
- UV reflective feathers cover and shade the skin
- Preen oil provides a layer of UV protection
- Some species have UV transparent corneas to avoid damage
Conclusion
In summary, ultraviolet light plays many important roles in the lives of birds. UV sensitivity allows birds to locate food, choose mates, navigate, and communicate using signals undetectable to humans. However, overexposure to UV can cause health issues for birds including eye damage and suppressed immunity. Protective adaptations like UV filtering eye pigments help mitigate the risks from intense ultraviolet radiation. Overall, the ability to see in the UV spectrum provides birds with a valuable extra sense that gives them an advantage over other animals that lack UV vision.
