<b>Nest box entrance matters: nest-site competition in sympatric breeding secondary cavity-nesting birds</b>

The results revealed that both Daurian redstarts and Eurasian tree sparrows avoided selecting nest boxes with a 10-cm entrance. However, the two species showed different preferences in entrance selection. Eurasian tree sparrows preferentially bred in nest boxes with a 3-cm entrance, whereas Daurian redstarts mainly selected nest boxes with 5-cm or 7-cm entrances.

The less competitive Daurian redstarts exhibited more intense defense behaviors than the more competitive Eurasian tree sparrows. This study provides key empirical evidence that nest-site selection is used to cope with interspecific competition between sympatrically distributed secondary cavity-nesting birds. The findings also contribute to a deeper understanding of adaptive behavioral strategies in birds under resource competition and offer a scientific basis for the ecological management of artificial nest boxes.</p>