When you're away from home and it's time to eat, how do you know where to go to find food?
Well, you probably just look for big, glowing fast food signs. What if you're a bird of prey, looking down on miles of grassland or desert, trying to spot a meal that's only an inch or two long?
While birds of prey do have unbelievably keen eyesight, that isn't always enough. They still have to know where to look, especially when they're scanning miles of unfamiliar territory, and the meal they're looking for is a tiny mouse or vole.
How Do Birds Do It?
By using chemical fast food signs to help them zoom in on the best places to find their prey.
Most birds that hunt in the daytime have eyes that are sensitive to ultraviolet light, in addition to the visible light that humans can see. Their most common prey are small rodents like mice and voles, which live in colonies. These rodents mark their territories using urine and waste. Under ultraviolet light, most of these scent markings glow with a blue light.
Fast Food Sign To A Bird
The main trails in each colony are "marked" over and over again by every passing user, so the glow from these high-traffic areas can get pretty bright.
The result is like a big glowing fast food sign to a bird of prey. Human eyes can't see these ultraviolet markings, but a hunting bird looking over miles of grasslands or prairie can see its prey's territory literally highlighted, as patches and lines that glow blue in ultraviolet light. Of course, the bird still has to catch its meal, but at least it knows where to start looking for it!