Friday, March 13, 2009

The Eyes of March Part Two

One of the first things that you learn when you join the education crew at The Raptor Center is what the three characteristics are that raptors have that distinguish them from other birds. All three characteristics have to do with the way that they feed. They have the sharp hooked bill, for tearing their prey into bite sized peices, the powerful talons, for catching and killing their prey, and their large powerful eyes, which help them to find their prey. The eyes are what I find the most facsinating, maybe it is because people are visual creatures just like many of the birds. Not only do raptors have much better distance vision then people do but they also have outstanding visual acuity. This allows them to see minute details and helps them to distinguish between the prey and the surrounding brush that it is typically hiding in.

Raptors have such good eye sight, in part, due to the comparative size of their eyes. A typical humans eyes make up about 1% of their body where a raptors eyes are 15% or higher. Large eyes do have some draw backs however, since the eye is so large there is not much room left in the socket for muscles, so their eyes are fixed in place. Since they do not have the ability to move their eyes they have evolved with extra vertabrae in their neck, raptors have 14 compared to mammals which have 7, which allows them to turn their heads over 180 degrees. Since the eyes are so large there is also very little room left in their skulls so raptors all have pretty small brains, including those wise old owls.

However eye size is not the only reason for raptors extraordinary vision, they also have an extremely thick retina, twice as thick as that of man. The retina is packed with visual cells called rods and cones. The cones, which are more important when it comes to the resolving power of the retina, are scattered around the retina with a high concentration in the fovea. The fovea is the part of the retina that is responsible for sharp focus, this is the part that humans use when we read. Raptors have many more visual cells in their fovea then people do, this is what gives them their high visual acuity. They also have a second fovea, called the temporal fovea. While the main fovea provides the raptor with excellent monocular vision the temporal fovea gives them what is termed as binoculer vision, which is what allows them to see at great distances.

So Now that we know a little about raptor eyes see if you can identify the birds whos eyes are pictured below. I gave you a little more to work with then the earlier eye quiz so maybe a few more people will give it a shot. Don't be afraid to guess because I would need to guess on most of these if I did not already know what they were.

Just to help you out a bit, these are all owls and not all of them are native to North America.
Good Luck


Anonymous said...

I didn't know this info..thanks. I think number 4 is a great horned owl..but I am not sure...

Lynne at Hasty Brook said...

1. Tawny Owl??
2. Barn Owl
3. Spectacled Owl
4. Eurasian Eagle Owl??
5. Great Horned Owl
6. Northern Hawk Owl

Ecobirder said...

Good Job Lynne!

Lynne at Hasty Brook said...

Thanks- I guessed on the Tawny and Eurasian Eagle Owl.