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We compared food availability and group density of Japanese macaques in Yakushima, southern Japan, among primary forest and two habitats that had been disturbed by logging and had different regeneration histories. The study was conducted in an undisturbed national park, forest that was logged 7-18 years ago and later naturally regenerated, and forest that was logged 19-27 years ago and later planted with Japanese cedar (Cryptomeria japonica) trees. The plantation forest was primarily composed of large Cryptomeria japonica trees at low stand density, while the naturally regenerated forest was composed of many small trees. The total basal area and number of trees in the primary forest were comparable to those in the plantation forest. Annual fruit production was greatest in the naturally regenerated forest, intermediate in the primary forest, and negligible in the plantation forest. Herb availability was high in the naturally regenerated forest, but low in the primary and plantation forests. The group density of Japanese macaques was high in the naturally regenerated forest, intermediate in the primary forest, and low in the plantation forest. Since group size in the naturally regenerated forest was small, individual density was almost the same as in the primary forest. These results suggest that the effects of regeneration on macaques vary between the two habitats. The plantation forest consisted mostly of Cryptomeria japonica, which supplies only flowers as food in a limited season, and had a lower density of macaques. On the other hand, in the naturally regenerated forest, fruit production and herb availability were high (probably because of the enhanced light conditions after logging), and the density of macaques was as high as in the primary forest.

It is well known that adult humans detect snakes as targets more quickly than flowers as the targets and that how rapidly they detect a snake picture does not differ whether the images are in color or gray-scale, whereas they find a flower picture more rapidly when the images are in color than when the images are gray-scale. In the present study, a total of 111 children were presented with 3-by-3 matrices of images of snakes and flowers in either color or gray-scale displays. Unlike the adults reported on previously, the present participants responded to the target faster when it was in color than when it was gray-scale, whether the target was a snake or a flower, regardless of their age. When detecting snakes, human children appear to selectively attend to their color, which would contribute to the detection being more rapidly at the expense of its precision.