On May 22, 2017, ignatz713 from White Plains, NY wrote:
Lovely, delicate little bird, new to me this year in Westchester, NY, but apparently here for a few years according to bird watching friends.
Only in this area for a few months, be sure to look for it. They swarm on food if you lay it out for them (squirrels took over all my bird feeders) and then flit off, the whites under their tails a sure identifier.
I hope to see them again next year, they make a nice addition to the 'usual suspects' and the more recent addition of the chickadee.
Welcome, Dark-eyed Junkos and to Google for allowing me to identify this bird by a vague description! My bird watching friend confirmed I was correct.