Just a few days ago I was eating lettuce fresh from the garden thanks to the very mild winter so far. But now those lettuces are frozen. The cold weather has set in over the last few days and most of the garden doesn't even thaw out during the day.
This seems to have finally caused the birds to start coming to the feeders, which had been extremely quiet until now. Don't forget that you might need to help them out a bit by topping the feeders up more regularly and making sure the bird bath isn't frozen.