Effect of forest management on a rare habitat specialist, the Bicknell's Thrush (Catharus bicknelli)

Abstract

Forest dwelling birds with narrow habitat preferences may be vulnerable to habitat changes from forest management. The Bicknell’s Thrush ( Catharus bicknelli (Ridgway, 1882)), a rare habitat specialist, occupies dense regenerating forest, including stands managed for timber. However, little is known of the impact of various forestry practices on Bicknell’s Thrush abundance. The purpose of our study was to determine how Bicknell’s Thrush abundance varied across the stages of a managed forest and to determine if abundance was affected by precommercial thinning, a practice that reduces stem density. Bicknell’s Thrush was most abundant in stands that were regenerating after being clear-cut 11–13 years earlier and of sufficient height and stem density to undergo thinning. Thrush abundance declined following thinning and was positively related to the amount of unthinned area remaining in the stand. Over all stand types, thrush abundance increased with increasing elevation and with the density of stems between 5 and 10 cm in diameter, but decreased with increasing amounts of bare ground. The results of this study suggest that Bicknell’s Thrush may benefit from the early successional habitat associated with managed forests, but may be negatively affected by treatments such as precommercial thinning that reduce stem densities.