Fig. 5. Horizontograms as seen from the nesting site (Nest), the feeding site (F9.5) and the various release sites (R1.9–R20.9). The abscissa shows the azimuthal direction; south defines 0° in a counterclockwise (positive) sense of rotation. Elevation angles of the skyline (ordinate) were measured every 10° of azimuth using a transit (Tracon S-25, Ushikata Co., Ltd, Japan). As the measurable angle of elevation using the transit was up to 50°, all elevation angles higher than 50° are represented as 50°. The numbers at the top of each column corresponds to the numbers of chestnut trees in Fig.3 (A.t.1–A.t.13). The asterisk shows the mean homeward direction of ants starting from their respective feeding or release site (see Table1). The high elevation angles for the north side were due to the building positioned next to the terrace, and those for the south to west side in the plots for R17.1 and R20.9 were due to a cherry tree (10.0m in height) located near the southwest corner of the terrace (x=24.5 and y=5.6; not shown in Fig.3), the branches of which overhung the west side of the terrace. For reference, vertical dotted lines are drawn at 0°, 50° and 100°.