Yesterday, I mentioned how important it is for spear fishers and diving birds to understand how water bends light. What I didn’t share was another page I ran into when searching for how a bird overcomes this obstacle. Prof. Boris W. Batterman seems to have only watched young birds fish:
When an eagle dives for a fish, and heads directly for the fish he sees, he misses because the fish is lower than it appears to him.
What does it look like when an adult eagle wants to catch some lunch?
Here’s what PBS.org says about the sea eagle of Tasmania:
The eagle has become so adept at fishing that it takes almost no time out of the day to obtain its food….The eagle starts at a higher angle and has a better idea of the actual location of the fish… As the eagle gets closer to the fish, it glides in at an angle that becomes steeper and steeper until the last second. When it grabs the fish, the eagle is very close to 90 degrees to the surface of the water and it knows just where to grab.
How did they know all that?
Here’s what we know about Common Kingfishers, one of the most beautiful fishing birds:
They have keen eyesight with polarizing filters to cut out water reflection and better see their prey. They also learn to compensate for refraction.
Polarizing eye filters? That’s cool. You ever worn polarized sunglasses and looked at sunny water?
Here’s what birds have to learn in order to deal with water’s light-bending properties:
A Bald Eagle with a freshly caught fish. Taken with Nikon D50, 80-400VR at the Airlie center, Virginia, USA. (Photo credit: Wikipedia)
the Bald Eagle: Their eyes don’t seem to have any adaptations to correct for refraction, but their brains do! The first fish young eagles successfully catch are often dead ones floating right on the surface of the water. They miss live prey a lot when they’re first learning to fish. Fortunately, with experience they slowly learn how to correct for refraction.
Looks like Pelicans do the same thing:
Pelicans have also learned that a steep dive angle, between 60 and 90 degrees, reduces aiming errors caused by surface water refraction. We know that pelicans learn this behavior because adults are better marksmen than young birds.
All these birds have to learn in just a short time how to deal with the way light is bent by water before they starve to death. Thank God, He designed these animals to quickly develop the skills they need to catch their food and protect their bodies!
List of some more diving birds:
- Cormorant
Red-billed tropic bird
- Osprey (I couldn’t pick only one: this one includes a story, this one’s more informative
- Blue-footed Boobie
- Tropicbirds
- Black-legged Kittiwake (seagull)
- Black Skimmer
God spoke: “Swarm, Ocean, with fish and all sea life!
Flying creatures, fly through the sky over Earth!”
God created the huge sea creatures,
all the swarm of life in the waters,
And every kind and species of flying creatures.
God saw that it was good.
God blessed them: “Prosper! Reproduce! Fill Ocean!
Flying creatures, reproduce on Earth!”
It was evening, it was morning—
Day Five. Genesis 1:20-23 The Message with CS4K Hebrew corrections
