Foraging mode shifts of four insectivorous bird species under temporally varying resource distribution in a Japanese deciduous forest

Abstract

Temporal changes in the foraging habitat of four forest bird species and the distribution pattern of arthropod populations were investigated. The abundance and distribution of arthropods changed drastically with the season within the forest. Lepidoptera larvae were most abundant in the canopy in the first three weeks after budbreak; their numbers decreased rapidly during mid-June. In contrast, on the forest floor, the larvae were abundant from early to late June. The foraging height of the Narcissus Flycatcher Ficedula narcissina changed in parallel with the distribution pattern of Lepidoptera larvae. Three other species, the Great Tit Parus major, Marsh Tit P. palustris, and Eastern Crowned Warbler Phylloscopus coronatus, however, did not change their foraging heights; they continued to forage in the canopy. These differences are probably due to the greater preference of the flycatcher for Lepidoptera larvae compared with the other three species. The three other species switched from feeding on Lepidoptera larvae to spiders or other arthropods in mid June, when the number of Lepidoptera larvae decreased in the canopy. The results of this study suggest that the abundance and distribution of arthropods and differences in foraging tactics among bird species considerably affect avian foraging habitat. The foraging behavior of three species of forest birds revealed species-specific responses to spatio-temporal fluctuations in the distribution of resources.