Studies on the linetransect census method of the woodland bird populations

Abstract

1. This report series treats the unpublished data in the study of the linetransect census method, which had been studied by the author and reported previously (Yui 1974, '77). This first report treats the diurnal change of the census effectivity, which is the ratio of individuals recorded in one census to the territory density in that area covered.2. In the breeding season, the diurnal change of recorded numbers in one census (viz, the census effectivity) according to day time is remarkable as shown in Fig. 1 (Asahikawa, Hokkaido, June, 1976) or in the previous papers. However, the relative dominance values of each species calculated by census data showed no significant difference by the time of day for many species inhabitting the study areas (Table 1 and 2). Therefore, it can be said that the pattern of diurnal change of census effectivity is almost the same in every species inhabitting the same study area.3. The diurnal changing pattern of census effectivity was calculated based on the data of Asahikawa (Fig. 1), and it gave the significant regression curve as follows;Y=139.7-10.67x+0.3816x2 F>P0.005This formula is standardized at 4:20, 30 minutes after sunrise, where x is time of day, when x is 4:20, Y becomes 100.4. To compare several changing patterns of census effectivity obtained at Fuji, Takizawa and Asahikawa, the time and value of the lowest census effectivity and the length of time from sunrise to the lowest time are shown in Table 4 for each area. In consequence, their values show a slight difference but not so large.5. With the investigations of changes micro light intensity at the twilight time and the bird activity at that time, it was appeared that there were no differences in their changes between latitudes or altitudes (partly in Table 3 and Fig. 2).6. In winter of 1975, the diurnal changing pattern of recorded numbers in one census according to day time was investigated at Takizawa. The pattern was different from that of the breeding season, and was divided into two groups of different changing pattern as in Fig. 3 and 4. First group, which include mainly resident small passerines and woodpeckers, showed no significant differnce by the time of day in the relative dominance values of each species calculated by the census data (Table 5). On the contrary, second group, which include mainly winter visitors and CORVIDAE species, showed significant differences each other in the same analysis, and decreased sharply its number in the course of day.