08 Aug Why Do Birds Of Prey Wear Hoods?
When we bring out our Saker falcon Halley for a lure flight for guests, she comes out with a hood that covers her eyes. Guests love to learn more about her hood and why she wears it. This brings us a great a opportunity to discuss eyesight and how the bird way of interacting in the world is incredibly different than the way humans do.
When we tell someone they have an eagle eye, we mean that their visual acuity is incredible high, or they picked up a minute detail others glossed over. It’s true, that birds of prey, such as eagles and hawks, possess extraordinary vision, allowing them to perceive their environment at high frequencies, typically around 80 to 100 Hz. This high flicker fusion rate means they can see more frames per second than humans, enabling them to detect even the slightest movements of their prey from great distances. When an eagle soars high in the sky, it can spot a small animal moving in the grass below, reacting almost instantaneously to swoop down and capture it. This heightened visual acuity is essential for their hunting strategy, which relies on speed, precision, and the ability to track fast-moving prey.
Eagle eyesight is among the best in the animal kingdom. They can see eight times better than humans, with vision that allows them to spot a rabbit from over a mile away. Their eyes are adapted to long-distance vision and tracking moving objects, making them formidable hunters. Eagles use their powerful vision to scan large areas from high altitudes, locating prey with incredible accuracy before diving at speeds over 100 miles per hour to capture it.
In fact, another way to conceptualize how good bird of prey eyesight is is found in Ed Yong’s book, An Immense World, which you probably have heard me talk about before. He describes how you can think of our field of vision as 360 degrees around us. If you put your thumb out in front of you in an outstretched arm, your thumbnail is one degree. If you paint your thumbail in black and white stripes, our visual acuity allows us to see 60-70 pairs of stripes, or 60 cycles per degree. The wedge tailed eagle of Australia holds the current record of 138 cycles per degree! Lions see at 13 cycles per degree and horses at 25.
The high frequencies, or flicker fusion rate, allows the birds of prey to see motion differently than we do. Their eyes are adapted to cope with such high-speed chases, featuring a more streamlined shape to reduce air resistance and specialized muscles that adjust the shape of their lens to maintain focus during rapid dives. What humans perceive as fluid motion, such as a flock of flying pigeons, looks like the stop motion of those early flipbooks of a cartoon, allowing them to single out the weakest bird.
In contrast, sea turtles, such as the green sea turtle, have a much lower flicker fusion rate, generally around 15 to 30 Hz. This lower rate is more suitable for their underwater environment, where light conditions are dimmer and movements are slower compared to the terrestrial habitats of birds of prey. This means that to a sea turtle, we are moving at light speed, jumping from feet per second as we swim past. Time truly is relative!
So what does this mean for hooding birds of prey? The way birds of prey not only sees sharply, but with a fast flicker fusion rate, they are constantly scanning the environment for the next opportunity for food or the next threat. Birds of prey are incredibly territorial, as you can probably tell from the screaming of red tailed hawks and perhaps red shouldered hawks. The latter is not quite as widespread as the former, but they make up for their lack of representation with a powerful voice! Imagine if you had to have your cellphone on you all the time and you never knew if the ringing was good news or bad news. When we train our birds of prey to wear their hood through choice based training, it’s like putting their phone on Do Not Disturb. They can travel comfortably through unfamiliar territory without the need to scan the environment, then we take it off and it’s time to fly, time to eat, or time to sit on the glove. The hood has a powerful context that tells Halley the Saker falcon that she is about to get a big a meal. It goes back on after that so she can travel back to her home of safety and familiarity.
There is so much more fascinating about the eyes of birds of prey, from how the left eye works differently than the right eye to how some birds evolved to see more on the ultraviolet spectrum and why. Our deeply researched Bird Biology course is coming out by the end of year and is designed for bird enthusiasts from the weekend birder to the professional bird trainer to enrich their lives and relationships with birds.