Just read this in the newsletter of Birders United www.birdersunited.com 
"Snowy owls have to eat about a dozen mice a day, about 20 percent of their total body weight, in order to keep their body temperature at a level at which they can survive in the harsh northern environment where they make their homes. But for unknown reasons, there has been a sharp drop in the number of mice in northern Canada. As a result, the snowy owls are migrating south earlier than in years past. After their migration the owls are weak and often lack the strength to hunt. Many are dying of starvation throughout lower Canada."

The Audubon Society of Missouri's Wild Bird Discussion Forum
ASM Website: http://mobirds.org/