Tree swallows would be unheard of in winter (and rapidly dead). As for tree
sparrows, I've had a small flock (most years 5 and this year 6) who come to
my feeders every day all winter long. They're usually the very first feeders,
pecking around under the feeders when it's still almost dark and before I've
put out new food, and then they continue to come (almost always together) on
and off till late in the afternoon. And they're so aggressive to each other,
running at each other with open bills and fiercely protecting little spaces
that appear to be about seven inches square for each bird.
I don't believe they're irruptive.