LAUSR

ABSTRACT Studies on foraging site selection during the breeding period of waterbirds can identify key ecological factors, providing a scientific foundation for their conservation and habitat management. The Scaly‐sided Merganser ( Mergus squamatus ) is a globally endangered species and serves as an indicator species in submontane valleys. However, research on the key ecological factors influencing foraging site selection at different breeding stages remains limited. In this study, ecological variables were collected from 226 sites in the Changbai Mountains, Northeast China, including 115 foraging sites and 111 control sites, across various breeding stages of M. squamatus . The analysis focused on foraging site selection during the egg‐laying, incubation, and brooding periods of M. squamatus . The results indicated that concealment (C) was the key ecological factor influencing foraging site selection for M. squamatus during the egg‐laying period. During incubation, the distance to potential nesting sites (DPNS) and the distance from buildings (DB) emerged as significant factors. In contrast, the brooding period highlighted the importance of the borderland ratio (BR) and heartland ratio (HR). These variations in key ecological factors at different breeding stages are likely due to the distinct physiological and behavioral requirements of M. squamatus at each stage.