Walking around old-growth forests this winter, if you're lucky enough to see fur-lined tracks leading to the base of a tree, or scat containing porcupine quills, look up. Scan the treetops. You might catch a glimpse of a marten or a fisher, two members of the mustelid family that roam Montana's winter landscape.
Martens don't hibernate; as the temperature drops, they'll find warmth under snow-laden ground cover. Long and slender and weighing only one or two pounds, martens need a lot of food - nuts, fruit, insects, voles, birds, and flying squirrels - to make it though winter. With small bodies and fast metabolisms, maintaining their body temperature in the cold is a challenge.
Their larger, rarer cousin, the fisher, is more elusive. So many fishers were trapped in the early 1900s that they were considered extinct in Montana until reintroduction efforts began in 1959, and 36 of them were restored to the western part of the state. Even today, it's unlikely that native fishers live in Glacier National Park. Fishers are the only constant predator of porcupines. Fast and low, a fisher can run circles around a porcupine until it collapses, after which it attacks its prickly prey's unprotected head.