Factors affecting the Mountain Hawk-Eagle reproduction under the cyclic fluctuation of Japanese Beech seed production

Abstract

We investigated the reproductive success of Mountain Hawk-Eagles Nisaetus nipalensis between 1990 and 2008 in Yamagata Prefecture, northern Japan. The existence of a correlation between fluctuations in Japanese Beech Fagus crenata seed production and nesting success was verified using observations of breeding attempts. A generalized linear mixed model (GLMM) was used to examine the relationship between nesting outcome and environmental factors (forest type, complexity of forest edges, nesting outcome in the previous year, and snowfall). To verify whether environmental factors affecting nesting outcome are influenced by variation in beech seed production levels, we analyzed the relationship between nesting outcome and environmental factors in the following three cases: (1) when beech seed production levels were high, (2) when beech seed production levels were low, and (3) when the beech seed production levels were not classified. Our results indicate that nesting success was significantly higher following a year when the level of beech seed production was high. However, the factor that was most strongly related to nesting outcome was nesting outcome in the previous year. In our study area, predominated by natural forest, when the beech seed production level in the previous year was low, GLMM analysis indicated that natural forest areas had a negative effect on nesting outcome, and artificial forest areas had a positive effect. The factors that affected nesting outcome differed depending on seed production levels in the previous year, and this suggested that the habitat used for hunting and/or the main prey species changed according to beech seed production levels.