A case report of an Eurasian jay () attacking an incubating adult and depredating the eggs of the Japanese tit ().

In May 2021, we opportunistically observed one Eurasian jay () attacking an adult incubating Japanese tit () and depredating nine tit eggs at a nest box where a woodpecker had greatly enlarged the entrance. After the predation event, the Japanese tits abandoned the nest. We recommend that when using artificial nest boxes to protect hole-nesting birds, the appropriate entrance size should be proportional to the body size of the target species. This observation gives us a better understanding of the potential predators of secondary hole-nesting birds.