The following is from the species account for Hairy woodpecker. I have seen Hairy's before that are stained from bark tannins of oak trees and they were tricky to id. It is possible you have a "dirty bird".
Kate
Aberrant plumages
As with Downy Woodpeckers (Jackson and Ouellet 2002), breast and other white markings of Hairy Woodpecker subject to discoloration due to soot from air pollution, natural fires, or prescribed burns; tannins from tree surfaces; and other environmental sources (JAJ). An apparently melanistic specimen from New Mexico had broadened black malar and anterior auricular stripes, reduced white on the head, reduced white with some black barring in the mid-dorsal stripe, and increased black on the sides and flanks. It was also unusual in having broadened white wing markings and an ivory-colored bill with brown tomia (Short 1969). A Hairy Woodpecker in New York that had white areas replaced by brown (LaFrance 1983) might have been stained, although genetically brown-breasted individuals are characteristic of some Central American and Pacific Northwest populations. Females from Nova Scotia (Royal Ontario Museum #24899) and Sapelo I., Georgia (American Museum of Natural History [AMNH] #487924) have an exceptionally white face with white superciliary stripe joining white malar stripe in front of eyes (JAJ). A male from Priest Lake, Idaho (specimen, Field Museum #127895) had a crown heavily mottled with white, white greater primary- and secondary-coverts, and white distal quarter of upper tail-coverts. A specimen from Madera, Chihuahua, Mexico (AMNH #706452) is an apparent gynandromorph, having red in nuchal area on left side, and white in same area on left side (JAJ).
Kate Peterlein
Flagstaff, AZ.
