HABITAT RELATIONSHIPS AND NEST SITE CHARACTERISTICS OF CAVITY-NESTING BIRDS IN COTTONWOOD FLOODPLAINS

Studied American kestrel Falco sparverius, northern flicker Colaptes auratus, red-headed woodpecker Melanerpes erythrocephalus, black-capped chickadee Parus atricapillus, house wren Troglodytes aedon and European starling Sturnus vulgaris in a mature plains cottonwood Populus sargentii bottomland along the South Platte River in NE Colorado. Density of large trees (>69 cm dbh), total length of dead limbs ≥10cm diameter and cavity density were the most important habitat variables; dead limb length (DLL), dbh, and species were the most important tree variables; and cavity height, cavity entrance diameter, and substrate condition at the cavity (live vs. dead) were the most important cavity variables in segregating cavity nesters along habitat, tree, and cavity dimensions, respectively, Random sites differed most from cavity-nesting bird sites on the basis of dbh, DLL, limb tree density (trees with ≥1 m dead limbs ≥10 cm diameter), and cavity density. Habitats of red-headed woodpeckers and American kestrels differed most from random sites. Based on current trends in cottonwood demography, densities of cavity-nesting birds will probably decline gradually along the South Platte River. -from Authors