Monday, February 15, 2010

John Blakeman on the Vision of Hawks, Rural Red-tail, and the Great Horned Owl in NYBG

While driving down the road with a friend, we saw this hawk flapping across a field, she very kindly perched for us.

Before the snow started again today, there was a small thaw which brought the snow depth down yesterday. Late afternoon there was an influx of birds going north, the vanguard of Starlings, much honking and three Canada Geese sighted and where ever the hawks were they have begun once again.

She scanned the area intently. We later saw what might have been a Merlin or a Peregrine as we started to roll again in the direction in which she seemed to be scanning the most intently.

She then took off, using the available cover, which Hawks everywhere appear to do, whether the cover is trees, or cliffs, or buildings.

Flapping at speed.

Navigating the branches.

A glide.

And then she disappeared into thicker woods.

Yesterday I talked about where Mrs. M appeared to be looking, but according to Red-tail expert John Blakeman things aren't nearly that simple--


One can’t be always so sure of just where a perched (or even flying) red-tail is peering. Direction of the head does not always reveal this.

This is because the retinas of hawks have two foveas, two centers of concentrated cones that can detect great visual resolution. Mammals have only one, in the center of the eye. That’s why we see so clearly (except with macular degeneration) in the center of our visual field, with things in the periphery a bit less detailed.

For red-tails, they can pear straight ahead, concentrating their focus on the high resolution vision centers at the back of the retina. But also, they can peer with great resolution pretty much straight out to the side, focusing matters of interest on the second retinal vision center.

Merely peering at a hawk on utility pole seldom reveals what she’s (yes, “she,” even though it might be an unknown “he”) looking at, at least when she’s looking at something in the horizontal distance.

Now when she turns her head down and appears to look straight below her, she is indeed looking there, looking straight ahead.

But I feel that the second retinal vision center used when looking sideways is probably even stronger, more detailed than the usual one on the rear of the retina. During migration in the autumn I notice that my falconry red-tail, when sitting on my fist, often turns her head sideways and peers up into clear blue sky with one eye. After a bit of searching, I, too, can often find what she’s looking at. It’s a mere speck of a migrating hawk some one or two thousand feet overhead. My red-tail sees it from afar and tracks it as it passes far overhead.

She prefers to use one eye, with the sideways posture when looking for these distant birds. She usually sees them far before I can. I can only know what part of the sky she’s looking in. Then, after a few minutes, as the hawk passes overhead, I can sometimes discover the mere dot of feathers above. Sometimes, without binoculars I can never see what she has been following so attentively.

So, the nice big haggard you photographed sitting so safely up there on the utility pole, just mere inches away from a lethal 12-hundred volt spike of AC current, could have been looking straight ahead, or just as effectively out to either side. No way of knowing.

A note about the conventional “she” designation for all hawks of unknown sex. This was surely not an imposed convention either of Chaucer, Shakespeare nor of Queen Elizabeth I. As influential as both were, the universal “she”was in general falconry practice for two or three previous centuries. It derives simply from the fact that female hawks, eagles, and falcons are larger and often preferred hunters compared to the smaller tiercels. Female raptors are just plainly superior, in almost every respect, so the “she” attribution was (and is) most appropriate.

--John Blakeman

From the intrepid Pat Gonzalez, our contributor from the New York Botanical Garden--

The native forest, trails and other portions of the NY Botanical Garden are covered in snow. In some sections, nearly two feet. (Friday, February 12).

I noticed that finally, the bird population is returning to normal. I saw lots of chickadees (yay!), cardinals, white throated sparrows, blue jays and others in many different sections of the garden. Lots along the wild wetlands trail which is a good thing as this winter, because of the pruning, it is temporary wasteland. So I was glad to see the old crew back!

Speaking of which, the female great-horned owl was inside an old tree. I usually stand about 12-15 yards away when I take photos, but getting to that spot was something else. I had to drag myself through mounds of snow. But I think it was worth it. Look at those yellow eyes! She is beautiful. I so hope she lays eggs in this tree. She's about 20 feet off the ground and is so well dug in, it is hard for blue jays, crows and other birds to get to her during their occasional dive-bombing.

I had taken a fair amount of photos and video and began to climb down, when two very nice ladies with binoculars introduced themselves to me. They said that they were both Docents at the garden and had enjoyed reading about my adventures and photos on pale male irregulars. Sadly, I forgot their names and had nothing to write with (sorry ladies, I'm AWFUL remembering names). As we started to walk away, a group of crows landing near mama owl. Some began their dive bombing, but couldn't go any where near where she was. I wondered if the male was nearby. The three of us looked but couldn't see anything. After a few minutes, they all took off.

Here's video of the owl from today which I've already posted on youtube.

If all goes well, and if it doesn't snow or rain, I'll be back at the Garden next Tuesday.

Thanks Pat!

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