<p>Moulting is a key event in the annual cycle of birds. Understanding the patterns and behaviours associated with moult provides essential insights into species conservation. During this vulnerable period, birds experience reduced movement performance due to feather loss. This vulnerability may be greater in large avian species if moult overlaps temporally with the breeding season. Despite these potential risks, the moult patterns and corresponding anti-predator behaviours of large waterbirds during this critical period, specifically cranes, remain poorly understood. The Black-necked Crane (<i>Grus nigricollis</i>) is the only crane species that resides on the Qinghai–Tibetan and Yunnan–Guizhou plateaus throughout its entire lifespan. Although recent studies have extensively explored the migration patterns and breeding ecology of this species, their moulting patterns and behaviours during the moulting phase remain poorly understood. Between June and September of 2022 and 2023, we investigated the moulting patterns of Black-necked Cranes in the Luanhaizi Wetland, Qinghai Province. Using high-resolution cameras and drones, we also investigated cooperative anti-predator behaviour between male and female adult cranes within four family groups at different moulting stages. We found Black-necked Cranes moulted flight feathers simultaneously around mid-July. Males (<i>n</i> = 4) started moulting 12 days later than females (<i>n</i> = 6), but both sexes experience a similar moulting duration, averaging 52.74 ± 6.30 days. In families where neither adult was moulting, both parents displayed anti-predator behaviours, with males displaying greater aggression. However, when one parent was moulting, the non-moulting partner assumed primary responsibility for protecting the family. These observations contribute valuable insights into the behavioural adaptations of Black-necked Cranes during the vulnerable moulting period.</p>