Constant-Effort Mist Net Bird Monitoring During the Breeding Season in a Lowland Deciduous Forest in Western Hokkaido, Japan

Using a standardized method to track long-term fluctuations in avian populations is important for proposing effective conservation strategies for birds. From 2013 to 2022, we conducted constant-effort mist netting and bird banding during the breeding season in a lowland deciduous forest in western Hokkaido, Japan. A total of 1,327 individuals of 30 species were banded or recaptured. Twenty-four species bred in the study area, two species periodically passed through the site, and four species were considered accidental visitors. Breeding adult Asian Stubtail Urosphena squameiceps and Eastern Crowned Leaf Warbler Phylloscopus coronatus declined significantly during the study period, although, there was no decline in their rate of reproduction. In the absence of forest deterioration, this suggests that their declines may have resulted from environmental changes along their migration routes or on their wintering grounds. Significantly more adult male Asian Stubtail than females were captured annually. This was assumed to be because of the unique breeding habits of this species. The recapture probabilities (p) of males were higher than those of females in four species (Asian Stubtail, Eastern Crowned Leaf Warbler, Japanese Thrush Turdus cardis, and Black-faced Bunting Emberiza spodocephala), but vice versa in Narcissus Flycatcher Ficedula narcissina. Among these five species, the adult apparent survival rate (φ) was highest for Black-faced Bunting and lowest for Eastern Crowned Leaf Warbler. The number of sites comparing the vital indices of birds in Japan should be increased in the future, as in the Constant Effort Sites (CES) ringing scheme in Europe and the Monitoring Avian Productivity and Survivorship (MAPS) program in North America.