Brown Creepers are the male countertenors of the bird world. Other birds can call in the upper register (Bushtits, Cedar Waxwings, Dark-eyed Juncos), but Brown Creepers actually sing in the stratosphere. If your ears are good, you can hear them concertizing now in the alder grove south of the kiosk. Surber Grove is another popular venue.
As talented as they are with their arias, though, Brown Creepers sing only part-time. They make their real living hitching up the side of tree like a miniature funicular, probing the bark with their curved bills as they search for insects and spiders. When they reach the top of a tree, they fly down to the base of another tree and start again, working around the tree in a spiral.
Sometimes males chase females around and around a tree in a kind of exuberant Ring-Around-a-Rosie courtship display. When it comes time to build a nest, they find a place on a tree where the bark has separated from the trunk. There, they construct a nest of leaves, bark, and twigs, shaped to fit the niche they have found.
Brown Creepers are hard to see against tree bark. Their brown/beige/black backs are the ultimate in camouflage dress. They prefer conifers for their activities, but at the Fill they settle for deciduous trees – lucky us. Any day I see a Brown Creeper is a great day.