Friday, January 06, 2006

Blakeman on GHO preening

Photo by Cal Vornberger

Donna Browne's obser-
vations on the great horned owl [see post of 1/4/05] are exceptional. At heart, she's a field biologist.
Two comments. First, her graphic depictions of the owl's preening are perfect. I'll add that the reason the bird spends an inordinate period of time preening the base of the tail, the rump, is that that is the location of the sebaceous or oil gland. Birds, especially big ones like hawks and owls, are much like turtles in that they carry their houses around with them. They live inside their feathers. The feathers must keep out wind and rain and keep in warmth. The owl's attentions with it's rump and tail attend to these essential matters.

Before flying out for a night of hunting, the owl was stropping its beak across the oil gland, loading it with water-repelling feather oil. Then it strokes other feathers, rubbing the oil into the feathers to keep the night's rain out of the soft, downy underfeathers. These are the ones that keep the bird warm. The outer feathers can get sopping wet and the owl will be just fine. But if oil isn't sufficiently kept on all of the body feathers, the bird will die of hypothermia.

My red-tail often spends an hour each morning primping and preening for the day. She appears as vain as any show girl prepping back stage for a frothy role. But it's not vanity or role-playing. This careful and prolonged preening is survival. For the hawk, she needs to keep her feathers as free of water as possible. If she gets water-logged, as sometimes happens in a summer downpour, she takes on the weight of the feather-embedded water, and that decidedly reduces her ability to fly. If she can't fly, she can't hunt and eat. It's all survival, not vanity (although it sure looks like that). A thirteen-year old school girl couldn't possibly be more attentive to a new hairdo than an owl or hawk must be to the oiled, water-free status of its feathers. Donna described the process wonderfully.

My second comment surrounds the sounds Donna heard the owl making. Great-horneds can have a rather large, and to me, unintelligible vocabulary. I won't suggest any specific meaning to the sounds Donna heard. But the fact that the owl was vocalizing at all is a rather clear indication that the bird has now taken up permanent residence in Central Park. Vocalizing at this time of the year is often a part of mate attraction. The bird sounds like it's lookin.' Should another great-horned of the opposite sex wander in (unlikely this late in the season), an owl pair almost surely would be formed.

But even it this big hooter doesn't encounter another of its own species this winter, it appears that it will settle down in permanent residence. Because it's vocalizing, it may pull in a mate next fall or winter. Great-horneds don't migrate in any concerted way. The young of the year just sort of wander around. I don't think many are likely to start flying down the Hudson or across the water over from in Jersey. But this one obviously got to Central Park, so if some other errant great-horned ever silently flies overhead, it may be lured in. The chances for this happening this winter are small. But if the owl hangs around all year (and I think he will -- he's got massive amounts of prime food with the rats), things, indeed, could get very interesting next season.

And I ponder once again, how could all of this wonderfully observable raptor biology can be happening in, of all places, Central Park? What a special place. Don't dismiss any of this, you New York residents. I marvel.

John Blakeman