The documentary on it is incredible. The fox RAN across the snow to get a look at this guy taking pictures. It was very interested and if the photographer had wanted he could have pet it. But he respected wild animals and just took its pic.
We had a hen who did this also. From the time the kittens were born, she would sit on them and keep them warm while the mother was out hunting, and then they'd trade places while the hen ate so the cat could feed her kittens.