Bird data : Japan, Sendai

Sendai is believed to be at the northern limit of temperate evergreen forests, and thus the area harbors fewer wintering forest birds. The avian fauna includes a small proportion of winter migrants, which do not remain in Sendai for long periods of time. For these reasons, we limited the study period to the summer from 10 August to 22 September 2007, continuing into the middle or late breeding season; i.e., birds that had migrated to the area during the summer had not yet left. Point censuses were conducted at each of the 20 study sites. At each site,we conducted 15-min point counts on three different days at the same location; thus the total survey time at each site was 45 min. Point counts were conducted from 06:00 to 09:00 h, and strong windy or rainy days were avoided. Both appearance (direct observation of a bird) and song (identified by listening) within an approximately 20m radius (Katoh, 1996; Ichinose and Katoh, 2003; Arriaga-Weiss et al., 2008) were treated as occurrence events. The 20m radius was maximum distance which we can directly observe because of buildings and read traffic noise. Cumulative data for the total 45 min were used to calculate diversity and for subsequent analysis.