Using the effective accumulated temperature to predict the seasonal onset date for singing by the Japanese Bush Warbler

Abstract

Birds are known to respond to climatic factors such as ambient temperature and day length. In the context of global climate trends, understanding a bird species’ response to the local temperature is a basic ecological factor that has conservation value. As an index to determine the start of the breeding season for the Japanese Bush Warbler Cettia diphone, we created a model based on effective accumulated air temperature to predict the date of the species’ first song of the spring season. From the “Seasonal Front Watch” data set of the Japan Bird Research Association, we used recorded date of the species’ first song at 39 monitoring sites during the period of 2005 to 2019. For each recorded date of the first song, we calculated the effective accumulated air temperature within 80 km of the monitoring site. We then developed a model to predict the first song date in all parts of Japan by obtaining the equation for the relationship between the effective accumulated temperature and the average temperature at each monitoring site. We validated the model by using the date of the first song in 2020, and found that it predicted the date of the first song of the Japanese bush warbler better than the average date of the first song over the period from 2005 to 2019. The result indicated that the effective accumulated temperature is an accurate method to predict the date of the first song of the warbler.