新潟市の海岸林における鳥類捕獲数の経年変化と森林遷移との関係

Abstract

Chronological trends in the number of birds captured (newly released) and their relationship to forest succession were studied in a coastal forest that is used by many migratory birds near the city of Niigata, Japan. Significant chronological trends in the number of individuals captured during the period 1991–2005 were seen for seven bird species in spring and six in autumn. Particularly, higher negative correlations between the number of birds captured and the dominical year were obtained for bird species showing decreasing trends. Bird species preferring sparse woodland, forest edge, or scrub, tended to decrease in spring. Herbivorous bird species, especially seed specialists, tended to decrease in autumn. These phenomena might be attributed to the dense growth of trees and shrubs and to the decline in plant species producing food for seed specialists on the forest floor caused by succession in the coastal Pinus thunbergii forest. Ground feeders tended to increase in both spring and autumn. Carnivorous bird species feeding on insects or earthworms tended to increase in autumn. This suggests that the coastal forest succession contributes to an increase in food resources for carnivorous bird species. The chronological trends in the number of birds captured might be influenced not only by forest succession in the study area, but also by the breeding results or seasonal changes in environmental selection of the bird species and nation-wide population changes. Comparisons with other research sites as well as the consideration of plant succession are important when analyzing bird-banding data as an indicator of long-term population dynamics or environmental changes.