A stand of ponderosa pines, which can reach heights of 180 feet, provides a variety of habitats for wildlife, including porcupines, pygmy nuthatches, red squirrels, and mule deer. Porcupines find abundant food there in the form of tree bark, buds, and twigs, and this slow-moving mammal climbs trees to escape danger. Because porcupines are very fond of salt, they are often killed on roads where salt has been used to thaw ice. Ponderosa pine forests are sometimes attacked by insects, making the pygmy nuthatch a beneficial resident because this small bird, only four inches long, eats insects that may attack the pines. Nuthatches are unique among birds for their ability to travel head first down trees. Red squirrels find abundant food in pine forests in the form of pine seeds, and a squirrel midden is a pile of cone scales left after the squirrel has eaten the seeds inside the cone. Red squirrels may also eat fungus, eggs, and other seeds.