flock of 100 robins

I was in Ann Arbor Michigan on Saturday 1-18 at Kerrytown and when I was getting into my car I noticed about 30 robins eating dried fruit on a couple of trees.  I looked around and saw that there was a flock of about 100 robins there on a cold January day.  There is still around 8 inches of snow on the ground and the temperatures will fall this week to very cold conditions.  What is going on with this?  I have never seen anything like this in Michigan.