Sunday, December 28, 2008

Portmann Red-tail Photography, Kestrels, and John Blakeman on Red-tail Hunting


A LEAP INTO THE NEW YEAR by Francois Portmann
www.fotoportmann.com/


How cool is this composition of Valkyrie the Thompkins Square Park juvenile female moving into flight!


Speaking of Valkyrie, for more on the meaning and derivation of her name see the comments section on the next post down.


Plus, many thanks to John Blakeman for a correction to that posting--I said that a juvenile Red-tailed Hawk's tail was longer and the wings shorter than the adults. I should have said instead that the juvenile's tail was longer and the wings were narrower than an adults.

Two completely different things.

Photograph by Francois Portmann
Male Kestrel blends right out of a Union Square reflection. Who would have thought?

I can't tell you how relieved I am to see how Kestrels are taking to the urban landscape as there is fear for the species in many of their former habitats. Now if we could just solve the problem of the common issue of their learn-to-fly-from-the-ground-up- fledglings stranding on the sidewalk we'd be near to all set in cities.

The Horvaths foster dozen upon dozen of these youngsters every year and do a grand job but in a perfect world we'd note all the nests and give each one enough branching opportunities to keep the youngsters (or more of them) "up there" instead of "down here" with people.

In the early 1980's, driving down a road in even well spaced suburban areas, let alone the rural areas, every other mile or so, there would sit a Kestrel hunting from a pole, a tree, or wires. This is far from the case now. There just aren't many there anymore. To see none in fifty miles isn't unusual.


Photograph by John A. Blakeman

VOLE TRACKS IN THE SNOW

Remember the James Blank anecdote about the Red-tail swooping seemingly blind into powdered snow and after several hops coming up with a rodent?


And here is Red-tail biologist John Blakeman's answers to our questions about the episode.

Donna,

About the Red-tail that blindly jumped into the snow and came up with a rodent. Did the hawk hear the little mammal under the snow?

Not very likely. Yes, owls are famous for this, but they have exceedingly accurate prey locating systems based upon prey sounds. Red-tails don’t have any of this, I’m sure. They can hear just about as well as we do. And with their smallish ears, they are not able to locate prey by their sounds any better than we can.

But they do have remarkable eyesight, that’s surely what was involved with this hawk and its successful killing of a rodent in the deep snow.

The rodent was almost surely a meadow vole, the primary prey of rural Red-tails. Under the snow, voles create tunnel runways, which after a few days of snow can become quite complex, creating an intricate network of buried, ground-level tunnels from one vole nest to another. I’ve attached a photo of these, taken when the snow was only about two or three inches deep. The runways became visible when the snow started to melt the tops off the tunnels.

Winter Red-tails learn that voles run in these tunnels, and when perched always look for the minute workings the voles reveal when they start to create the tunnels, or when they run in them, or, perhaps in this case, when they periodically “swim” up through the snow to poke a nose out into the cold, clear air, creating ventilation holes.

The hawk certainly didn’t hear the vole. Voles are very quiet in the snow. But she almost surely saw it excavating or moving the snow beneath the surface. From this, she could rather easily discern where the vole was working, allowing her to plunge her foot into the snow to see what she could grab. Being a Wisconsin Red-tail, she’s probably done this many times before.

In fact, this is a real factor in the over-wintering of Red-tails at higher latitudes. Across the northern tier of states, at the northern latitudes, Red-tails seldom, if ever, spend the winter up there. Too much thick snow. The majority of Red-tail prey animals, the voles, can easily avoid being taken by the hawks by remaining in their networks of runways or snow tunnels.

Where there is persistent winter snows, Red-tails have to leave for the season and go to generally snowless areas to the south. Now it’s not fair to say that Ohio, Indiana, southern Wisconsin, and this general latitude of states are snow-free in the winter. We’ve got an inch or two of snow on the ground here in Northern Ohio, and we have lots of winter resident Red-tails.

But our snows are seldom thicker than 6 inches or so, and when they are, they seldom last for more than two or three weeks. A warm air mass comes in and melts things down.

A healthy adult Red-tail can lay on enough fat in late fall to easily go without food for a week or longer, if snow conditions would require that. But longer than 7 to 10 days, things get a bit desperate, and the bird simply starts flying south to snow-free latitudes where the voles are unprotected.


John A. Blakeman

2 comments:

Sally said...

It sounds like RT's hunting voles under snow cover is a bit like my dog digging up the moles in the yard as they tunnel!

Donegal Browne said...

It does doesn't it.

Speaking of hunting rodents under snow, if you get a chance watch the PBS Nature episode, Christmas in Yellowstone. There is a sequence of a Red Fox hunting mice or voles in deep snow. Fox do it by sound like owls and it's hilarious. The fox listens, gets ready, leaps into the air and plunges straight down,nose first, with only his back legs and tail poking up out of the snow. You can tell when he gets one, as he's chewing when he comes out. :-)