Same with the goldfinches that come to my feeders. There were 11 of them on the 23rd - a regular group of 8 plus 3 apparent interlopers with much loud squabbling, then none for several days and the nyger seed they like seemingly not touched. Then this morning 3 of them are back. Perhaps they've been conserving energy in the cold weather... but a cold golfinch still needs to eat and they normally munch the contents of a couple of feeders in as many days. A mystery. Sparrows here have been around, though less frequently. I hope yours are back soon.