Abstract
The breeding success of the Japanese Golden eagle, Aquila chrysaetos japonica, designated a precious natural product and a class IB endangered species in Japan, has declined rapidly during the last three decades. Of the likely factors causing this breeding failure, a rapid decrease in the foraging habitat, caused by an increase in coniferous plantations with closed canopies, was recently noted. In 2002, the forest agency attempted to make forest gaps, using line-thinning, to form a foraging habitat for Golden eagles in order to improve their breeding success in the Kitakami Plateau, in Iwate prefecture. In order to evaluate the efficacy of line-thinning in creating a foraging site for Golden eagles, we determined numbers of hares and snakes, which are the main prey of the Golden eagle in this region, and the foraging activities of Golden eagles in three plots, i.e., line-thinning, control, and normal foraging habitat plots. In the line-thinning plot, the number of hare pellets, which was used as an indicator of the number of individual hares, increased remarkably the year after line-thinning, although the number decreased in the second year after line-thinning, and finally ended up being similar to that before line-thinning. Snakes were rarely observed in any plot. The foraging activity of Golden eagles in the line-thinning plot was lower than in the normal foraging habitat plot throughout the study period. Therefore, unfortunately, the line-thinning practiced in this study was not effective for increasing the foraging activity of Golden eagles, although this trial was successful in causing a temporary increase in the prey animals. Therefore, it is necessary to devise a method for making foraging habitat as quickly as possible, while promoting practical forest management, in order that Golden eagles may continue to exist in this area.
