Laura Erickson's For the Birds

Tuesday, December 4, 2007

Dave Benson's new book!

We got a lot more snow today, but I had an errand out near the airport, and since I was out that way anyway, I stopped at Wild Birds Unlimited to get more sunflower seeds. And what should be sitting right there on the counter but Dave Benson's excellent new book, Owls of the North: A Naturalist's Handbook, published by Sparky Stensaas's Stone Ridge Press, in the new Bird Nerd Natural History series. It's a small book filled with wonderful photos and a wealth of information about all the owls we'd find in Minnesota or anywhere else in the upper Midwest or northeastern states and provinces.

Dave Benson is a wonderful naturalist who's been studying and talking about owls for almost as long as I have. A couple of the points he makes are a little different from my own understanding--I learned in Gary Duke's avian physiology class that owls do in fact have plenty of cone cells in their eyes--not as many (relative to rod cells) as many diurnal birds do, but plenty enough to allow fairly decent color discrimination. (In the human eye, we have about 120 million rods and only about 6 million cones.) According to this 1987 paper in The Condor, a Great Horned Owl's photoreceptors are 7 - 8% cones, and the authors suggest that although color vision isn't acute, it may "broaden the spectral window through which visual information may be gained; this might be particularly useful during the occasional daylight hunting forays of this species."

Also, banders are discovering that Saw-whet Owl feathers have wonderful patterns when they look at them with a black light. If the feathers have "color" in ultraviolet wavelengths, these owls almost definitely are able to discern it, which may allow them to recognize sex and even discriminate among individual Saw-whets.

Dave discounts one possible function of owl feather tufts helping owls to appear a bit more catlike, but that happens to be a theory I think makes a lot of sense. The times I've seen Great Horned Owls on the ground, feeding on rabbits, they DO have a very fierce, catlike appearance that must seem rather fearsome to an approaching fox--it might just give the owl an extra few seconds to finish swallowing and take off without being eaten. Of course, as Dave notes, looking like a small mammal could be dangerous for any bird, but even large predators seldom mess with cats without taking at least some self-protective measures, so during the vulnerable moments when an owl is on the ground grabbing and eating its prey, there might well be some benefit to holding those tufts like a cat's ears. Indeed, when a cat rears to attack, it pulls its ears back in almost the exact same way as my education screech owl Archimedes pulls his feather tufts back whenever I have to grab him to put his jesses on. As Dave notes where he discusses the defense posture, owls also hiss when they're approached, another catlike behavior, and Dave notes that some other Great Horned Owl vocalizations have made him think an owl was a cat.

Dave quotes a researcher who found that one tame Long-eared Owl taloned anyone who touched its tufts. My own Archimedes doesn't seem to react one way or another when I touch his feather tufts--he seems to like any part of his head stroked. I've read many sources suggesting that the feather tufts have a sensory function, and my own feeling is that this is almost certainly true, but is only one of several possible functions for those tufts. Like Dave says, though, nobody knows for sure.

Dave covers a lot of owl basics and presents a lot of solid information about each species, and even where his opinion about an issue is different from mine, there is plenty of food for thought, so the book is well worth $16.95. It's available in bookstores and online.

The photo on page 65, which Sparky took of a roosting Saw-whet Owl, is apparently of the exact same bird I photographed in Two Harbors a couple of years ago, resting on the exact same branch. It was a hotline bird, so dozens of birders saw it. Sparky is taller than me so his angle is slightly different, but it was really cool to see this particular bird in this wonderful book, which would fit perfectly in a Christmas stocking.