Mountain bluebirds are migratory and range from as far south as Mexico in the winter, on up through Alaska in the summer. This one, a male, was in Yellowstone in late May. They are small birds that prefer open habitat and are often seen on the ground, either in the grass or on small perches like this rock. The males are a vibrant blue in color while the females are a duller blue with more grey on the chest, head and back.