Abstract
In Castanopsis sieboldii forests on Miyake Island, where the effects of the 2000 volcanic eruption still persist, a gall midge Schizomyia castanopsisae has invaded from the Ryukyu Islands, resulting in the failure of acorn production. Owston’s Tits Sittiparus varius owstoni, which prefers C. sieboldii forests for breeding and relies on its acorns as an important food source in autumn and winter, showed an approximately 40% decrease in breeding pair density in 2023 and 2024 compared with 2015, but only along two survey routes containing continuous C. sieboldii forests. This suggests that changes in food availability caused by the gall midge may have affected this species. However, Cinereous Tits Parus cinereus, which does not depend on C. sieboldii, also showed a large decrease (50–75%) along the same routes with continuous C. sieboldii forests, indicating the possibility of indirect effects of the insect invasion. Further studies are needed to clarify the mechanisms and extent of these impacts.
https://ror.org/02hcx7n63 
