I was going through pictures and found this one of a pretty roughed-up Red-breasted Nuthatch.
I went to the Smithsonian Field Guide to the Birds of North America by Ted Floyd because it is the first guide I pick up when I want to know how many molts a bird goes through each year. This bird was pretty raspy looking so I wondered if it was perhaps molting.
The first thing the guide told me is that red-breasteds have only one complete molt a year, so no, I don't think it was molting. As I looked at the date on the picture, it told me the timing for a molt didn't seem right either (it was June) - many birds don't molt during breeding season because of the energy required to carry out each activity.
So I think it was probably just a kind of scruffy-looking individual, most likely a female considering the dull colors, who may have been starting to show the wear-and-tear of breeding activities.
Anyway, I got a chuckle out of some of the descriptions of the nuthatch in the Smithsonian guide. "All nuthatches are ovoid and pot-bellied..." I felt sorry for these little guys being called egg-shaped, like Humpty-Dumpty with wings! And pot-bellied too!
The guide continues, "All vocalizations nasal and petulant", which Merriam-Webster defines as "insolent or rude in speech or behavior."
Male Red-breasted Nuthatch (August)
The poor little Red-breasted Nuthatch. Defamed in such a manner and only a tin-horn yank-yank to defend its honor! So it's a little round through the middle and got a little attitude - sounds like me to tell you the truth. But these traits are why the Red-breasted Nuthatch makes it on to many birdwatcher's favorite birds list.