”Latitude-Longitude Index” for wintering distribution locations of various bird species in Japan

The species temperature index (STI), which is the mean temperature of the distribution area for bird species, has been calculated to evaluate the response of birds to climate change. In Japan, the STI for the breeding season has been calculated based on the results of the “Japan Breeding Bird Atlas.” Since the effects of climate change are more pronounced during the wintering season of birds (Lehikoinen et al. 2021), it is important to know the STI for the wintering season in Japan. We surveyed to determine the wintering distribution of birds in Japan between January 2016 and February 2022. However, the 40 km grid to collect distribution information used in this survey included areas of low to high elevation in the steep terrain of Japan which made the temperature differences within the grid too large to show STI. Since the Japanese archipelago extends from southwest to northeast, the distribution of any bird species in the Japanese archipelago can be indicated by the value obtained by adding latitude and longitude. Therefore, we calculated ”Latitude-Longitude Index” values that describe the distribution of various bird species during the wintering season in Japan to replace the STI. Here we present this method and propose it is a useful approach for studying the effects of climate change on birds.