Use of aquaculture ponds by globally endangered red-crowned crane (Grus japonensis) during the wintering period in the Yancheng National Nature Reserve, a Ramsar wetland

Conversion of natural wetlands to artificial wetlands is a global phenomenon that leads to loss of natural habitats for waterbirds, while these alternative wetlands may buffer the adverse effects of natural wetlands loss by providing waterbirds with suitable habitats. Yancheng National Nature Reserve (YNNR), a Ramsar wetland in China, is the largest wintering area for the globally endangered red-crowned crane (Grus japonensis). A remarkable part of natural wetlands within the YNNR has been reclaimed into aquaculture ponds in recent decades. In order to better understand the utilization of aquaculture pond by cranes and identify beneficial management actions, we investigated the wintering crane occurrence in ponds and quantified pond characteristics as mainly influence factors from November to March in 2017–2018 and 2018–2019. A total of 198 ponds were measured (91 in 2017–2018 and 107 in 2018–2019), out of which 42 ponds were found to be used by 48 groups of cranes (16 in 2017–2018 and 32 in 2018–2019). Family groups with 2–4 individuals of cranes were mostly encountered (91.7%) of all the group types. Wintering crane abundance in the aquaculture ponds was higher in 2018–2019 (105 individuals) than that in 2017–2018 (59 individuals). Five factors including water depth, species abundance, species richness, structures and distance to road were identified to influence use of ponds by cranes. However, crane occurrence was significantly associated with only water depth. This study recognized aquaculture ponds as a potential habitat for red-crowned crane. Efforts should be channeled into the sustainable development and maintenance of aquaculture ponds. More specifically, we recommended appropriate management practices to benefit wintering cranes by sequential harvesting of aquaculture ponds, maintaining aquaculture ponds in the buffer zone and keeping the water at a low level.