Have you ever wondered what birds will do for a drink of water in the dead of winter when everything has been frozen up for days? I have wondered that myself. As far as bodies of water go, a gurgling creek might stay open in a deep freeze - at least in some spots. I witnessed a solution to the problem that never occurred to me one winter when everything had been frozen for days.
Even when the air temperature stays below freezing, the sun's rays can be strong enough to allow sap on the sunny side of a tree to rise. If the tree also has some type of injury to it's bark, the sap will weep out and run down the outside of the tree. You probably have seen trees like this.
On this particular day, I watched bird after bird take turns going to a tulip poplar that was oozing sap to slake their thirst. The photos are admittedly not very good, but they do clearly depict how the birds solved their problem.