Willow flycatcher (Empidonax traillii) surveys in the Colorado River delta: implications for management

A subspecies of willow flycatcher, the south-western willow flycatcher, has become endangered in the U.S. The objective of this study was to determine the presence/absence of this subspecies in the Colorado River delta. Surve ys were conducted in June-July 1999 and in May-June 2000. We detected a tot al of 50 birds, most likely south-western willow flycatchers, from May to J une and none in July. It appears that the birds found in the delta were mig rants. It is important to restore the intensively used stopover sites for t he recovery of the subspecies. Additionally, we postulate a migratory route throughout the estuaries of Sonora. (C) 2001 Academic Press.