Saturday, January 26, 2008

A Red-tailed Hawk and its Nictitating Membrane

On Sunday the 20th I decided not to go any place specific, instead I would just drive around and see what I could find. This usually works out pretty well in the warmer months, particularly in spring and fall during the migrations, but it is kind of risky when the temps are below zero. Birds tend to congregate during the winter in Minnesota. Eagles and water fowl congregate at the few open water spots that they can find. Passerines and Accipiters congregate where there are well stocked feeders. In the Twin Cities area the only birds that you can regularly find away from open water and feeders during winter are woodpeckers, crows and red-tailed hawks.
Fortunately on this day I found a cooperative red-tail that was perched close to the road. Red-tailed hawks are usually pretty easy to find but they are usually perched higher up and can be skittish. This red tail was at about eye level if I was standing and did not flush when I pulled the car to the side of the road and began shooting through the open passenger window.

Hawks, like most animals, will show you signs that tell whether they are stressed or not. Bending down into a take of position, head bobbing, and wing flapping are some of the signs that a bird may be stressed. Bill clacking and dive bombing are signs of extreme stress and usually mean that you are probably too close to a nest or young. Other actions, like standing on one foot and warming the other one with their body or preening typically mean that the bird is calm. I figured that since this bird began to preen that he was not concerned with the presence of my vehicle. I included this picture of the bird preening because he had his nictitating membrane closed. The Nictitating membrane is like a third eye lid that many birds have as well as some lizards, sharks and mammals. Here is a little closer view of the nictitating membrane.The nictitating membrane is transparent eye lid that closes horizontally across the eye instead of vertically like a normal eye lid. It is used to protect the eye and to help keep it moist while maintaining the birds sight. I have seen many birds who have using their nictitating membrane lately. I am guessing that the reason is either they need to moisten their eyes more often during the winter when the air is very dry or as protection from the cold subzero wind. Humans have the remnants of a nictitating membrane, it is the small pink flesh in the corner of our eyes.

Craig of Craigs Birds has a nice picture of a sandhill crane with its nictitating membrane closed. It is pretty cool you can check it out at http://craigsbirds.blogspot.com/2007/07/nictating-membrane.html. He has a great blogsite and even had barred owls nesting in his yard last year. I was so jealous. The only thing that was living in my yard last year was a chipmunk.

5 comments:

Rick said...

I noticed that in some house sparrow today too. I am think it is related to the cold weather.

Craig said...

Very neat shot of the hawk with the nictating membrane. I haven't noticed that with cold but I have noticed it in the summer with Sandhill Cranes when the bugs are plentiful. I caught a picture of a crane (didn't know it at the time though) showing its membrane.
http://craigsbirds.blogspot.com/2007/07/nictating-membrane.html

Ecobirder said...

Rick, I think in this case the cold did have a lot to do with it but as Craig noted there are other reasons too.

Craig, I added your link to the original post so that people can get to your post a bit easier.

Lynne said...

I've seen so many red-tailed hawks along the roads lately but never at eye level. Beautiful photos!

Mike said...

Interesting photograph showing the nictitating membrane of the red tail. Thanks for sharing. Also very interesting seeing the Sandhill Crane's too. If you are interested in seeing a bald eagle's nictitating membrane, I just posted a photograph made at close range: http://www.mikephoto.com/bald-eagle-nictitating-membrane/
Cheers