We counted all individual birds detected by sight or sound
within a 10-min period. Observations were separated into
three time segments of 3-, 2-, and 5-min (Ralph et al., 1995)
and were recorded in bands of 25, 50, 100, and >100 m. At
the beginning of each field season, observers were trained
in distance estimation, refreshed their bird identification
skills, and conducted simultaneous counts to strengthen observer
consistency.