My co-worker has been occasionally bringing her dog Chester to work. This afternoon Chester was tied up outside the office door, where he spent most of his time lying on the porch facing a big bush. A few minutes ago, I heard a loud, repeated chip note from this bush, an unusual sound for this part of the yard. On closer scrutiny, I spied the noisemaker, a male Common Yellowthroat. This tiny bird, smaller than the palm of my hand, was perched on a high branch of the bush and looking right at Chester, scolding the dog with a repeated "alarm" chip. He carried on like that for over five minutes, his fervor diminishing over time, until eventually he gave up trying to warn Chester away from the bush and flew off.
This wasn't a territorial thing, because the bird doesn't live in that bush, which is so close to my office window that I would have heard him singing loudly and often. At least one yellowthroat lives in the shrubs along the edge of the lawn, however. My guess is that the bird noticed the dog and chose to bravely fly up to confront it, or at least to make enough noise that others in the area would be alerted to the dog's presence.
Chester didn't budge during any of this. I'm not sure he even registered that an assertive little warbler was making a lot of noise right over his head, let alone that he himself was the cause.
Even I can tell
the bird's sounding an alarm,
chipping, "Watch out! Dog!"