Can Sandhill Cranes Predict Weather?

On Feb 5, 2012, we saw sandhill cranes migrating north. That is very early to be headed north compared to our sightings over the last few years. Normally, they wait until March.

We saw them migrating south around Jan 1, 2012. That was about a month later than usual.

The winter here has been very warm in February and March (as of March 15). Here, on March 15 in the Atlanta area, it is sunny and 81 degrees.

How did the sandhill cranes know it was going to be a mild, short winter?