Nuttall's Woodpecker, Picoides nuttallii

Males have the red patch in the rear of the crown, while the adult female, feeding a juvenile male on the left has no red patch at all. Juveniles of both sexes can have a red patch; males tend to have a patch that is larger and further forward, as with the nestling on the left, compare the one below.

This nestling, with a smaller patch not quite as far forward, could be either a male or a female, according to the discussion in Pyle, Identification Guide to North American Birds.

This nestling, being fed an earwig by the male parent, appears from the patch to be the same one as is pictured two above. The different locations of the adult male and juvenile patch is clearly illustrated here.

The bird below, a lone visitor at our back yard fountain, appears to be a juvenile male from its red patch, which extends forward beyond the eye.

Three adult females, above and left.