Some are permanent residents, while others may migrate south in winter or move down from higher elevations. Their range covers most of North America including southeastern and southcentral Alaska, southern Canada, most of the United States and the central mountains in Mexico. Some have begun to move more southeast in Indiana and neighboring states. Buidin "et al." did a study of how far north the northern saw-whet owls breed and they found that they can breed northward of 50° N, farther than ever recorded before. Their range is quite extensive and they can even breed in the far north where most birds migrate from to breed. They are an adaptive species that can do well in the cold. There are two semi-isolated permanent populations in the eastern part of the United States. This first is a population along the West Virginia border in the Allegheny Plateau. The second population is in the higher elevations (>4000 ft) of the southern Appalachian Mountains of western North Carolina, eastern Tennessee, and southwestern Virginia. Although there are abundant populations in the Northern and Western Regions of North America, in some counties of North Carolina, it is currently listed as a threatened species due to a decline in suitable habitat. This is due to loss of boreal forests from hemlock woolly adelgid, logging, and pollution. Northern saw-whet owls lay about four or six white-colored eggs in natural tree cavities or woodpecker holes. Males will often sing from a nest sight and cache food in nest sites in order to attract a female. The father does the hunting while the mother watches and sits on her eggs. Females can have more than one clutch of eggs each breeding season with different males. Once the offspring in the first nest have developed their feathers the mother will leave the father to care for them and go find another male to reproduce with. This type of mating is sequential polyandry. They compete with boreal owls, starlings and squirrels for nest cavities and their nests may be destroyed or eaten by those creatures as well as nest predators such as martens and corvids. Saw-whet owls of all ages may be predated by any larger species of hawks or owls, of which there are at least a dozen that overlap in range including "Accipiter" hawks, which share with the saw-whet owls a preference for wooded habitats with dense thickets or brush. Recently few nesting northern saw-whet owls have been found in breeding nest boxes in the Southern Appalachian mountains.