The American red squirrel (Tamiasciurus hudsonicus) is one of three species of tree squirrel currently classified in the genus Tamiasciurus, known as the pine squirrels (the others are the Douglas squirrel, T. douglasii and Mearns's squirrel, T. mearnsi). American red squirrels are also referred to as pine squirrels, North American red squirrels, boomers, and chickarees. They are medium-sized (200–250 g) diurnal mammals that defend a year-round exclusive territory. The diet of these tree squirrels is specialized on the seeds of conifer cones. As such, they are widely distributed across North America wherever conifers are common, except on the Pacific coast, where they are replaced by Douglas squirrels. Recently, American red squirrels have been expanding their range to include primarily hardwood areas.