The marten, which is about the size of a house cat, is a highly skilled climber but is just as comfortable hunting and traveling on the ground. They often den in tree hollows, among rocks or even in “borrowed” nests from squirrels or birds. Mid summer is their mating season, and while their gestation period is only two months, they exhibit what is known as delayed implantation, where the embryo doesn’t start to develop until late winter. Young are typically born in late March or early April