Friday, November 09, 2007

The Downy Woodpecker Makes A Visit

Downy Woodpecker, Picoides pubescens, female calls.

Suddenly there she is on top of the wire circle. She looks down at the suet and begins to descend towards it using beak, toes, and tail.
First she tries to access the suet with both feet still on the wire and bracing her tail on that side as well----She leaned. Unsatisfactory. (She's got a very hummingbird-like expression on her face. I'm wondering if it's manifested by focus over a lengthy beak.)
She moves her left foot to the feeder and braces her tail straight down against the wire. This seems to work better and she begins eating, her head and chisel shaped beak rapidly jackhammering the suet. She has a very long tongue which is barbed and sticky. It's barbed and sticky in order to retrieve insects and larvae from crevices and from under bark. Woodpeckers have bones in their tongues and like hummingbirds they fork in the rear and curl up around the skull. Add the muscles that control the tongue and you have the hyoid apparatus.
She stares fixedly and then goes for the jackhammer movement once again.

There's an abrupt stop and she stares north and east. The directions from which most predators come from in this location . Look at those toes. Her feet are zygodactyl, two toes in front and two in back like those of parrots and cuckoos. In the photo above she's extended the rear toes laterally or in an ectropodactyll manner.

When I zoomed in on one of her feet, it was very odd because it looked like she was wearing little scaly work gloves. The photo is somewhat deceiving.

Here is a better angle and you can see the double toes in the back. I couldn't find out if it is the case in woodpeckers but parrots are hatched with three toes to the front and one to the back. The far third toes in front gradually migrates to the back during chickhood.

Her foot back in a clutch, she goes back to eating.

Downy tails and those of other woodpeckers are marvels. They are a built in brace. But a brace capable of fine motor movement due to large muscles that control the stiff feathers, in some cases independently. The two longest center feathers are pointed. They have longitudinal ridges with hooked barbs that curve in towards the vertical surface creating more tail strength. The center feathers have a nearly unique molt pattern in that they don't molt out until the new ones have fully grown in.
Woodpeckers have a very jerky movement when navigating a tree as they hop with both feet while their tail supports them during the hop. And I would assume also adds some propulsion in the direction of the hop to help counteract gravity. A finely tuned system or gravity would just dump them on the ground unless they took to their wings.

And a favorite wonder I'd never noticed before, a pair of false eyes on the back of her head, formed by tiny dots of white feathers.
As Woodpeckers are all specialized in their specie's choice of habitat, they are more sensitive than some other species when it comes to possible extinction due to habitat loss. And even if their habitat remains but is fragmented to many edges, as cavity nesters, they are vulnerable to cavity predation by aliens such as the European Starling which can devastate their reproduction success.
Donegal Browne

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