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Archive for the ‘Avian Anatomy and Physiology’ Category

With the falconry hunting season coming to a close, it’s time for most falconers to put their birds up for the moult. Since Gregg and I are first year apprentices who had to trap immature hawks, our red-tails were both born in spring of 2009. Because our  hawks are less than a year old, they still have their immature plumage. For a red-tail this means they don’t have a red tail yet.

When the moult begins, a falconer raises the bird’s weight higher than it was when they were hunting. This is possible because the bird’s response to the falconer is no longer important, and the bird needs every bit of extra energy the food provides to grow strong, healthy feathers.

For some falconers, this is when they release their bird. A released falconry bird has the advantage of coming out of the winter hunting season healthy and well cared for, while also having matured in its ability to catch game and always having guaranteed food from the falconer. 70-90 percent of wild raptors will die within 12 months of being born. They die from natural causes such as predation, and from unnatural causes like electrocution. Thankfully,the first year mortality rate is much lower for falconry birds. When a bird is trapped for falconry, it has a much better chance of eventually becoming part of the breeding population.

During the moult, a hawk will typically lose one feather at a time, maintaining the ability of flight throughout the process. There is a pattern that they will fall out in, which changes depending on whether the hawk is a true hawk (accipiter), falcon (falco), or broadwing hawk (buteo). A red-tail is a boadwing hawk, so Heath’s moult should follow a predictable pattern.

I would like to invite any readers of this blog to follow along with me during Heath’s moult. I will be posting pictures during some of the different phases of the process. Let me know what you think!

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Did you know that hawks can see roughly four times better than humans?  Their eyes exhibit a number of peculiarities, one of which stood out to me in a recent presentation by Dan Hart of the America Bald Eagle Foundation (www.baldeagles.org).  Raptors have the ability to perceive the near ultraviolet part of the light spectrum (from 320-400nm), which is outside of the visible spectrum for you and me. 

This capability is put to work in intra and inter-sexual signalling, navigation, prey identification, the control of circadian rhythms and intraspecies communication.  The capability is provided through an additional cone, which sees UV instead of the typical red, green or blue that our cones detect.

Eye of a Red-Tailed Hawk

Several days ago I was speaking with Luke, a veterinary student at the University of Georgia, and he conjectured that the American Crow is likely the most colorful and bright bird in the sky when viewed through a raptors eyes.  Isn’t that an amazing thought?  Anything looks different from a perspective other than the one we’re used to!

Another important difference is the raptor’s superior flicker fusion frequency.  Humans have a flicker fusion frequency of 60 hz whereas raptors is significantly higher.  We see, in essence, more slowly than they do.  A television image, for instance, that appears seamless and full motion video to us would appear jerky to them, whereas a raptor would see something much faster, like the flicker of a squirrel tail, would appear seamless to them and blurry to us.  Even the incandescent lights we use would appear to flicker to the raptor, like a bad flourescent light would appear to us.

There is so much more to discover about the hawk’s eyes and I will look to post more later if there is interest.

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