The Position of the Sun

I learned in  teaching my kids science that birds ( and other animals, also, I'm assuming) know when spring is by the position of the sun. The temperature doesn't seem to have anything to do with it. 

My kids, on the other hand,  took the temperature last week as a license to get into anything and every thing as long as it splashed. 

 ~

At 6:30 this morning, I heard a robin, as I sat thinking about my day. It caught me somewhat, it's still so cold out, I feel like it is still winter. 

But the robin didn't need to see things, such as crocuses and jonquils, popping up through the leaves to tell it the season. It paid no attention to the blowing snow, and freezing temperature. There are no outward signs and wonders of spring except for the position of the sun. Yet that robin came and placed itself where it belonged, without question or reasoning. 

Do we know the season by the position of the Son?