Three cases of collared owlet depredation on the green-backed tit within nest boxes.

The main cause of the reproductive failure of cavity-nesting birds is nest predation, even though cavity nests protect from numerous predators. To study the breeding biology of the green-backed tit ( Parus monticolus ) and to promote the reproduction of some other avian cavity breeders, we placed 245 nest boxes in the Zixi Mountain, southwest China. We collected breeding data by regularly checking the artificial nest boxes, three cases of green-backed tits being predated by collared owlet ( Glaucidium brodiei ) were confirmed by the video recordings. Larger mammals, chipmunks, squirrels, sparrowhawks, jays, and snakes have been identified as common predators of cavity-nesting birds in high-latitude regions of the northern hemisphere. Limited research in tropical and subtropical regions, particularly in Asia, has demonstrated squirrels and snakes as common predators of cavity-nesting birds. A gap in avian predators to cavity-nesting birds exists in the current knowledge. Hence the three cases of collared owlet's depredation reveal a new danger to green-backed tits, broadening our knowledge of the dynamics of cavity-nesting birds. In all three cases, the artificial box's entrance hole was only 5 × 5 cm in size and has not been expanded or poked. These findings provided evidence that the collared owlet is the predator of nestlings and adult green-backed tit breeding in artificial boxes, which emphasized a reevaluation of predator-prey interactions. Therefore, for effective breeding of the green-backed tit, we suggest to choose a hole size of 3 × 3 cm that is appropriate for its body size.