Abstract
1. The differences of the census effectivity between bird species, vegetation features and observers respectively are not dissolved by employment of average recording distance of each species as the observing radius (Fig. 1, 2, 3 and Table 1).
2. Then, it was considered that it is desirable to take a common distance (not far than 50m) for all species at the linecensus.
3. The relative values of the census effectivity in a 25m observing radius were calculated standardizing as 100% at a 50m (Table 2). The differences of the census effectivity between species, vegetation features and observers respectively can not be reduced in the case of 25m radius compared with that of 50m (Table 2, 3, 4).
4. The author recommends 50m as an observing radius in the linecensus compared with the other radius as a 25m, because it can get many sample counts and stabilize the results than another radius, and can eliminate the forest margine effect of road side.
