Nest Sites and Population Demographies of White-Breasted and Pigmy Nuthatches in Colorado

Abstract

In north-central Colorado, white-breasted nuthatches [Sitta carolinensis] nest in cavities in living ponderosa pines [Pinus ponderosa], while pigmy nuthatches use cavities in dead pines. Pigmy nuthatches [S. pygmaea] nest in a greater variety of sites than white-breasted nuthatches. Both species avoid cavities with openings facing north or west. Pigmy nuthatches in this study had higher population densities than white-breasted nuthatches, owing to greater abundance of nest sites, more flexibility in nesting conditions and smaller territories in the former species. Populations of the 2 spp. declined at different times of the year, associated with territorial and winter flocking behaviors.