Birds

Sitting here looking at snow and could not help but noticed that the bird feeder is swamped with birds. Today is the first cold day we have had in a while, just checked the thermometer and it was at about 8*. Past few weeks has been in the low 30's and we did not see one bird. Now that the temp has dropped they are everywhere. Happened the last time we got cold, so much so that we found several of them that apparently froze to death. Anybody got an explaination????