Spatio-temporal Variation in Egg-Laying Dates of Nestbox-Breeding Varied Tits (poecile Varius) in Response to Spring Pre-Breeding Period Temperatures at Long-Term Study Sites in South Korea and Japan

Climate change can alter and disrupt the phenology and phenological interaction between organisms from various trophic levels in forest ecosystems. In temperate forests, the breeding phenology of birds is correlated to local microclimate, especially spring temperature to match the timing of food availability. Recent studies revealed that the temperature warming is more pronounced in high-elevation areas (elevation-dependent warming), while the breeding phenology shift of birds in this condition needs further investigation. We studied the annual change in the egg-laying dates of varied tits (Poecile varius) and a pre-breeding temperature index in three plots located along with the elevational gradient in South Korea and a low-elevation plot in Japan. We found strong support for disproportionate rates of changes in higher elevation for warming trends in pre-breeding period and advances in egg-laying dates over the last decade. Next, we compared three segments of 36-year data from Akazu Research Forest. The evidence from pre-breeding temperature during 36 years indicates that we could detect the change in thermal environment and breeding phenology with longer years of data, especially in lower elevation regions. This result shows the need for long-term research to understand the change in local temperatures and the ecology of forest birds. Our study presents evidence of elevation-dependent phenological advance in avian breeding activities and discusses the need for systematic long-term research on multiple taxa and climatic drivers in Asia.