I watch the artist as she watches the bird. Her pen glides over the sketchpad, unfettered. Rough black lines erupt onto the paper. She fills in the details, big-to-small, like this: big circles and triangles, then boxes of feather tracts, to eyes and talons, clawing to fly and escape. It is an incredible likeness. The Brown-headed Cowbird browsing in the grass is immortalized by her careful gaze. Paper and pen translate it into an individual.
Therein lies one value of sketching. Illustration for field guides is done with museum specimens. The bird you see depicted in your Sibley or National Geographic is a composite of dozens of dead birds. It is perfectly average. There is nothing especially streaky or dark or large-billed about it. Sketching a moving bird in the field reveals the imperfections in a carefully measured ideal.
And the bird is alive, too. It struts with its chest forward, and every time it bends down to nibble something in the grass, its head tips forward and its tail tips upward, like a seesaw. The large chest and short tail result in a comical effect in which the bird appears to struggle to keep from falling forward when it walks.
The pen sees the cowbird moving, and more. It only has the time for a few hasty judgments before the cowbird flies away. In that precious few moments, it must remember as much as it can, contained within large arching circles and rectangles that capture the rough size and shape of the cowbird. Through sketching, an observation is born.
That observation is not measured in careful inches or centimeters. It is nothing more than an impression that stores all the oddities of the bird, its useless details, its unique body shape. It is with this impression that the next cowbird will be compared. After a few thousand sketches, maybe a mutual understanding will be reached between the artist and the cowbird. Then the pen will have served its job.