What’s the last thing a fish sees…

January 25, 2012 | Greg Dodge

before it’s snatched up by a heron?

Great Blue Heron.

Great Egret peering into the water.

The heron in the above photo is actually looking down at me, not a fish, but you get the idea. The heron was in a pine tree above the path in Explore the Wild.

What’s interesting about the photo is that it clearly illustrates the fact that herons have binocular vision and can see objects beyond and below their bills, helpful if you make your living plucking fish out of the water. Among land or air based predators binocular vision is the norm.

While herons’ eyes are placed on the sides of their heads allowing them to see potential trouble heading their way from the side, they are far enough forward that both eyes can be used to peer down into the water at their prey. Two eyes are better than one when trying to gauge position and distance.

Herons are able to detect trouble approaching from the sides as well as watch for prey below.

Birds such as mallards, and mammals like rabbits, have their eyes placed high and laterally dead center on their heads allowing them a 360 degree view of the world. It’s tough to sneak up on either. Although herons can’t see directly behind themselves, a simple turn of that long flexible neck lets them quickly checkout who’s sneaking up from behind. They give up some of their ability to see potential predators approaching from the rear in order to have bino vision, but you still have be be on you tippy toes to sneak up on them.

OK, so a heron can see with binocular vision helping it gauge the distance and location of the object of its attention (fish in water), but how does it deal with refraction? You know, when you put a stick into the water it looks like it’s bent. The light is bent by the different (relative to the air) refractive properties of the water. Unless the fish is on the surface, say it’s 6 inches or so under the water, it isn’t actually where it looks like it is. How does the heron allow for refraction when jabbing at a fish in water?

I’ll leave that one to you.

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