I'm not great at warbler IDs yet, but I was wondering if this could be a Yellow-Rumped Warbler? It had some subtle yellow on the top of its head too, but I did not get to see the back before it flew away. This was taken in upstate New York in late April.
I almost didn't pay attention to this little bird—I assumed it was a chickadee but realized it was actually too small to be a chickadee, so I snapped a quick photo. This bird was fluttering about the lower tree branches by our pond.