Climate change influences phenology of many animals and plants all over the world. In this study, we analyzed changes in the timing of first calling (reproduction) of Japanese tree frog, Hyla japonica in Japan over the period of 54 years observed at 60 sites of Japan Meteorological Agency. We performed hierarchical Bayesian analyses to quantify shifts in the date of first calling and effects of multiple climate factors on H. japonica phenology.

In contrast to past studies that showed phenological trends became earlier in various organisms, we found that timing of first calling of H. japonica have shifted later with a rate of 0.4 days/year. This trend was consistent in space.

Temperature, humidity, precipitation and sunshine duration were related to date of calling such that frogs call earlier when these variables were high. Contrasting to the increasing trend in temperature, there were decreasing trends in other variables, which can result in shifting calling date later. We suggest that the retrogressive shift in timing of first calling of H. japonica may be caused by decline in multiple climate variables, especially in humidity, of which effects exceeds that of increasing temperature which will shift phenological trend earlier.