Psaltriparus minimus
Bushtits are really very small birds, gray all over. The flock onto the suet feeder, where I have seen as many as 16 at a time. They feed right-side-up, or hanging upside down like a nuthatch or a chickadee. They travel in flocks, and the only reason this one was by himself is that the feeder was too crowded for him to fit, so he is waiting... Males have black eyes, and females have a yellow iris, so I think this one is male.