Cavity-nesting birds and the cavity-tree resource in plains cottonwood bottomlands

Densities of, and potential nesting substrates for, cavity-nesting birds were examined in a mature plains cottonwood (Populus sargentii) community in northeastern Colorado. Although snag (dead tree) densities were low (0.66/ha), the cavity-nesting guild included 7 species with densities ≤ 463 birds/100 ha. This finding suggests that cavity nesters are not limited by snag densities. Most (94.2%) of the nest substrate for cavity-nesting birds was provided by live trees with large, dead limbs (≥ 10 cm in diam). Both total dead limb length and the number of trees with dead limbs were highly correlated (P < 0.001) with the number of cavities excavated. Large trees (>55 cm in diam at breast ht [dbh]) and dead limbs 15-30 cm in diameter were preferred for cavity excavation. Because snags were a minor component of potential nest substrate, snag management may not be a useful concept for cavity-nesting birds in cottonwood bottomlands, and snag retention aspects of habitat models would be relatively unimportant for this forest type. Live-tree management is recommended.