Like American football players, many birds of prey have dark black markings just below their eyes. Most of these birds are falcons and all of them hunt flying animals. Given this, ornithologists have argued for years that these markings, known as malar stripes, help prevent light from bouncing off of feathers just below the predator's eyes and blinding them on sunny days. It is a nice idea and makes a lot of sense. The problem is that there hasn't been any proof that this is how the birds actually use these markings... until now.
Got my sunnies on!
Image courtesy of US Fish and Wildlife.
The team behind the new work reasoned that if malar stripes really evolved to reduce solar glare, then they should be bigger and darker in regions with particularly high annual solar radiance than they are in areas with less radiance. To test this out, they turned to the most widespread falcon on the planet: The peregrine.
The peregrine falcon is present almost everywhere globally*. As such, the researchers set up an international effort to source photos of peregrine populations that have long been established in locations with radically different levels of annual solar radiation. They found that the size and prominence of the malar stripe was greater in areas with lots of annual solar radiation and lesser in areas with little annual brightness.
So we now know that, aside from being able to fly at speeds of 390 kilometres per hour, these birds are also effectively wearing sunglasses. You can almost here the Top Gun theme playing as they bolt through the sky…
The academic paper published online in Biology Letters in June.
*Which is really saying something given that we almost drove the bird into extinction with DDT poisoning during the 1960’s.