In winter, porcupines seek out ready-made dens, such as this tree cavity. (Porcupines are one of several wildlife species – from invertebrates and salamanders to birds and other mammals – that rely on tree cavities for shelter.) Porcupines’ tree dens are often conspicuous, as they may strip bark near the entrance, and their scat often overflows from the cavity and accumulates at the base of the tree. Trails leading to porcupine feeding trees radiate out from the den tree and are often marked with urine, scat, and quills. Eastern hemlock is a favored winter food, and the discarded tips of hemlock branches (“nip twigs”) litter the ground beneath trees where porcupines have eaten the tender needles and buds. Like all rodents, porcupines have constantly growing incisors, which they use to scrape and eat the cambium, or inner bark, of trees, leaving distinct parallel grooves in the wood.