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

In May 2021, we opportunistically observed one Eurasian jay ( Garrulus glandarius ) attacking an adult incubating Japanese tit ( Parus minor ) 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.