What is happening to my lawn in the winter
 

The pictures say it all! In the summer I feed it, cut it, etc etc. This year is really bad! I haven't touched it apart from raking up the leaves. Any ideas? Are the roots being eaten by pests?

Today

http://i.imgur.com/M5nL9JV.gif

Last Summer

http://i.imgur.com/B9k6FzX.gif