Abstract
Many waterbird populations have become increasingly dependent on agricultural habitats for feeding. While habitat destruction has been proposed as a key reason forcing waterbirds to move from natural habitats to agricultural habitats, few have used long‐term data to test this hypothesis. The Siberian crane (Leucogeranus leucogeranus) is an IUCN Critically Endangered species. About 98% of its global population winters at Poyang Lake, China. Recently, many cranes shifted from feeding in natural wetlands to agricultural habitats. Here, we integrate bird surveys, Vallisneria tuber (the traditional food of cranes in natural wetlands) surveys, water level data, and remotely sensed images from 1999 to 2016 to explore the drivers of this habitat shift. Changes in Siberian crane numbers in natural wetlands and agricultural fields indicated that the habitat shift occurred in the winters of 2015–2016. Analyses using generalized linear mixed models suggested that crane numbers in natural wetlands were positively related to tuber density and the interaction between dry season (October–March) water level and tuber density. The changes in tuber density and dry season water level in 2015–2016 indicated that tuber disappearance may have been the primary driver of the habitat shift, with a smaller effect of high water level. Submerged plants at Poyang Lake have degraded seriously in the past two decades. The plant degradation at Shahu Lake, a sublake of Poyang Lake, may have been caused by high spring water, high winter temperature, and low summer temperature. However, the drivers of tuber disappearance at Poyang Lake may not be restricted to these variables. Because Poyang Lake is an important refuge for many waterbirds in the Yangtze River floodplain, it is urgent to take effective measures to restore its submerged plants and ecosystem health. Agricultural fields can be important refuges for Siberian cranes, mitigating the negative impacts of wetland deterioration.
Highlights
Many waterbird populations have increasingly become dependent on agricultural habitats for foraging during wintering and migration seasons (Amano, 2009; Bellio, Kingsford, & Kotagama, 2009; Czech & Parsons, 2002)
Because Poyang Lake is an important refuge for many waterbirds in the Yangtze River floodplain, it is urgent to take effective measures to restore its submerged plants and ecosystem health
We suggest that a variable may have been the driver of the habitat shift (a) if it is an important factor determining the abundance of Siberian cranes in natural wetlands, and (b) if it changed substantially when the habitat shift occurred in a way that might have negatively affected crane foraging
Summary
Many waterbird populations have increasingly become dependent on agricultural habitats for foraging during wintering and migration seasons (Amano, 2009; Bellio, Kingsford, & Kotagama, 2009; Czech & Parsons, 2002). Siberian cranes at Poyang Lake largely returned to shallow waters in the winter when tuber abundance rebounded (Burnham et al, 2017). We suggest that a variable may have been the driver of the habitat shift (a) if it is an important factor determining the abundance of Siberian cranes in natural wetlands, and (b) if it changed substantially when the habitat shift occurred in a way that might have negatively affected crane foraging (e.g., abnormally low tuber density or biomass). Because the data were consistent with a tuber collapse being the primary driver of the habitat shift, we further explored whether the tuber collapse may have been driven by abnormal water levels or temperatures, important factors influencing the growth and production of Vallisneria (Cao, Li, & Jeppesen, 2014; Xu et al, 2016; Zhao et al, 2017)
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