 More than 120 bird species have been sighted on the refuge during summer months, but only a few dozen hardy species remain through winters.Mature white spruce in the forested lowlands provide cover and den sites for marten, and trapping these and other furbearers remains important to the economy of people in the region.In fact, refuge lands have been used for centuries by Koyukon Athabascans for hunting, fishing, trapping and other subsistence activities.