The relation between the fall in breeding success ratio of mountain hawk eagle (Spizaetus nipalensis) and forest structure of its home range

The kumatakas' breeding success ratio of the western Hiroshima prefecture has fallen rapidly as another of bird of prey reported since 1990s. The author has studied the relation between the success ratio and the vegetation in the home range for 25 years to make clear the reasons why its ratio have dropped recently. Firstly the authors have confirmed that the ratio has kept near 100% in 1980s, and its level have fallen about 50% in 1990s and many kumataka couldn't breed in 2000s. Secondly the authors have confirmed the home range of three site of the kumataka. The area of site A is 635 hectares, site B is 839 hectares and site C is 1,108 hectares. Thirdly vegetation within the range is divided into 10 categories and data would be related to the success ratio have been collected. The authors have analyzed these data and divided the usable vegetation (forest) and un-usable one. The former categories consisted mainly of under 10 years artificial forest, broad leaf forest, harvested area and so on, the latter categories contained mainly over 1O years artificial forest and forest without care. Forest cares, such as thinning, pruning and tending play very important roles to keep their success ratio. Finally the author made clearly conclusion as follow. (1) Wide area of the under 10 year artificial forests and broad-leaved forests were existed in 1980s. (2) Un-usable forest area for the kumataka have increased and exceeded usable forest area. (3) Un-usable area of site A has been counted less than 400 hectares since 1990s. (4) Usable area should be kept over 400 hectares for maintenance breeding success ratio. (5) Usable area needs over a half of the home range. (6) If forestry activities, such as harvesting, thinning, pruning and so on, shall be carried out at the level of 1980s, its ratio shall go up to higher level like the 1990s. (7) Rehabilitation of forestry is the important matter for the kumataka.