Changes in distribution and abundance in China

Of 180 records of wintering Baer’s Pochard in China, 51 counts came from 1986/87 to 1992/93, 53 from 1993/94 to 1998/99, and 76 from 2002/03 to 2010/11 (Table 1). The totalled provincial annual counts for each period suggest a dramatic decline in numbers and a severe contraction in range (Table 1). During 1986/87 to 1992/93 large flocks were reported from several provinces, but by 1993/94 to 1998/99, large flocks were only reported from Hunan Province, and substantial numbers only reported from Anhui Province in 2002/03 to 2010/11, where they were concentrated at Wuchang and Fengsha Lakes, and Liangzi Lake in Hubei (Table S1 in online Supplementary Materials). Only 194 Baer’s Pochards were observed during an extensive survey of the middle and lower Yangtze River floodplain in January 2011. Special surveys of Liangzi Lake by the Wuhan Bird-watching Society and visits to Wuchang Lake (Anhui) and Baiquan (Wuhan) during winter 2011/12 failed to produce a single record before 10 February 2011. However, we failed to find this decline in periodic compilation from 2002/03 to 2010/11 (Table S2 in online Supplementary Materials), even though there were extensive coordinated surveys in all periods. We believe that in recent years, the more frequent and complete surveys in Anhui and Hubei Provinces lead to a better detection of this species.

Table 1. Annual maximum counts of Baer’s Pochard from each province of China, for each of three periods during 1986/87 to 2010/11. Summing provincial annual maxima across a series of years is likely to overestimate the true numbers present at any time, underlining the seriousness of the decline observed in these values. ‘--‘ indicates no records (either no survey or no birds) in that province; 1: Waterbird Specialist Group of Chinese Ornithological Association (1994); 2: Li and Jiang (Reference Li and Jiang1990); 3: Wang (Reference Wang2000); 4: D. Lee (in litt.); 5: Wang et al. (Reference Wang, Ge, Li, Lang, Lin and Lu1998); 6: Goodwin (Reference Goodwin1987); 7: Scott (Reference Scott1989); 8: Li et al. (Reference Li, Bloem, Delany, Martakis and Quintero2009); 9: W. Liu (in litt.); 10: Lei and Yang (Reference Lei and Yang1999); 11: Su et al. (Reference Su, Wang, Lü and Wang1998); 12: Miyabayashi and Mundkur (Reference Miyabayashi and Mundkur1999); 13: J. Thalund (in litt.); 14: Barter et al. (Reference Barter, Chen, Cao and Lei2004); 15: Wuhan Bird-watching Society, Lading, [email protected]; 16: field survey by J. Lei 2010/11; 17: China Ornithological Society (2004); 18: Tao Xudong, [email protected]; 19: field survey by Barter et al. (2005, Reference Cao, Barter and Lei2008, Reference Cao, Zhang, Barter and Lei2010, 2011); 20: field survey by Barter et al. 04/2005; 21: [email protected]; 22: [email protected]; 23: [email protected]; 24: Hexin17, Musenlin, [email protected]; 25: [email protected]; 26: midway, [email protected]; 27: [email protected]; 28: Shuiqiongchu, mmchong, [email protected]; 29: Anon (2005); 30: Ba et al. (Reference Ba, Zhang, Qian and Li2003); 31: Cui et al. (Reference Cui, Yang and Chen1992); 32: Zhang (Reference Zhang2007); 33: Wei (Reference Wei2008); 34: Zhang (Reference Zhang2008).

National counts outside China

Totalled annual maximum counts from all range states outside China fell from 719 in 1999/2000 to 2004/05 to 48 in 2005/06 to 2010/11 (Table 2). Regular coverage at key former wintering sites and casual observations from many potentially suitable sites suggest that few Baer’s Pochards have wintered outside China at all in the six years up to and including 2010/11. Bangladesh supported 3,000 birds in 1996, but only 20–30 have been reliably reported in recent years (P. Thompson in litt.) and in India (where over 1,400 were counted in 1995 and 1997) the species has almost ceased to appear (maximum 3 individuals) in the Asian Waterbird Census (AWC) reports (Li et al. Reference Li, Bloem, Delany, Martakis and Quintero2009). There were no records from Myanmar in January 2006 and 2007, compared to 129 in 2001 and 500–1,000 during the 1990s (Li et al. Reference Li, Bloem, Delany, Martakis and Quintero2009). In Thailand, Baer’s Pochard was still regularly seen in the 1990s (e.g. 596 counted in 1998; Li et al. Reference Li, Bloem, Delany, Martakis and Quintero2009), but has virtually disappeared, with annual total counts of fewer than five in the last four years (P. Round in litt.). In Laos, Baer’s Pochard has not been recorded in suitable habitats in the last 10 years (W. Duckworth in litt. J. van der Ven in litt.). Although always rare historically in South Korea, the frequency of occurrence has also declined (N. Moores in litt.).

Table 2. Annual maximum national counts of Baer’s Pochard from all range states since 2000. Summing national annual maxima across a series of years is likely to overestimate the true numbers present at any time, underlining the seriousness of the decline observed in these values. *indicates data from Asian Waterbird Census data until 2007, ** indicates results from Asian Waterbird Census data until 2002, -- indicates no data available. Data sources are as follows: 35: Anon (2005); 36: P. Thompson (in litt.); 37: Japan Anatidae census; 38: Duckworth (Reference Duckworth2009); 39: N. Moores (in litt.).

Potential causes of the declines within China

Declines and range contractions of Baer’s Pochard over the last 25 years in China mirror trends amongst several wintering waterbird species there (e.g. Fox et al. Reference Fox, Cao, Zhang, Barter, Zhao, Meng and Wang2010, Zhang et al. Reference Zhang, Cao, Barter, Fox, Zhao, Meng, Shi, Jiang and Zhu2010, Cong et al. Reference Cong, Cao, Fox, Barter, Rees, Jiang, Ji, Zhu and Song2011, Reference Fox, Cao, Zhang, Barter, Zhao, Meng and WangWang et al. in press Reference Zhao, Cong, Barter, Fox and CaoZhao et al. in press), although consistent data on distribution and abundance are patchy. In China, hunting and habitat loss are considered the major causes of decline amongst many wintering waterbirds (Cao et al. Reference Cao, Zhang, Barter and Lei2010). Between 336 and 4,803 Baer’s Pochard (mean 1,630, n = 7) were reported shot annually between 1981 and 1987 along just one section of Hong Lake, Hubei Province (Li and Jiang Reference Li and Jiang1990), and according to an experienced local hunter, 3,000 individuals were hunted annually some years ago at Rudong and nearby area, just north of Shanghai (Lei in litt.), suggesting hunting mortality has contributed to local extinctions within China. Winter diet of these diving ducks is poorly known beyond water plants, grass seeds and molluscs (Qian and Zhu Reference Qian and Zhu1980, Zhuge Reference Zhuge1990). Changing water chemistry, pollution, intensified fishery management, submerged macrophytes and the changing general ecology of many wetlands in the Yangtze River floodplain (e.g. Fang et al. Reference Fang, Wang, Zhao, Li, Tang, Yu, Ni, Liu, Xie, Da, Li and Zheng2006) have undoubtedly inflicted major habitat changes upon this species throughout China.

Wuchang, Fengsha and Liangzi Lakes are now of outstanding importance for Baer’s Pochard as daytime roosting sites (Table S1). Day-long observations at Wuchang Lake in February 2010 and 11–13 January 2011 showed that they slept and rested well offshore, but never fed throughout daylight hours (pers. obs.). All birds departed at dusk for unknown feeding areas, along with Baikal Teal Anas formosa, Falcated Duck A. falcata and Pintail A. acuta and returned before dawn.

It is noteworthy that records in 2010/11 and 2011/12 indicate large fluctuations in numbers of Baer’s Pochard at key sites such as Liangzi and Wuchang Lakes, which are well covered by experienced observers and active birdwatchers. These records suggest that Baer’s Pochard is very mobile and shows limited site fidelity between winters. The absence of this species in extensive surveys at these key sites in 2011/12 (Cao in litt., Lei in litt.) again emphasises the uncertainty of information on this species.

The quality and frequency of surveys in key sites have improved since 2000. Nevertheless, an assessment of other potential sites and targeted surveys for the species at those sites is a high priority, because surveys have so far been partially incomplete (even the very comprehensive ones in 2004, 2005 and 2011), Though other large catchments, such as the Yellow River catchment, may provide sites for this species, both freezing temperature and absence of observations by birdwatchers in winter indicate the low probability of finding this species there.

Factors affecting Baer’s Pochard outside the winter quarters

Although Baer’s Pochard have disappeared from many of their former winter quarters, widespread reductions have occurred simultaneously throughout its non-breeding range, suggesting that factors operating on the breeding grounds or associated with migration are also important. Outside China, the most dramatic declines occurred prior to 2000 but dramatic contractions in range and a conspicuous crash in numbers occurred in China after the early 1990s. Although it is too late to identify the factors responsible, it is a high priority to visit breeding areas to assess what remains of this now tiny and fragmented population, and to establish factors threatening survival and breeding outcomes.

The global reduction in the abundance and distribution of Baer’s Pochard shows no sign of slowing or ceasing, and we have no understanding of the causes of these trends. Our results indicate that the world population of Baer’s Pochard is far less than the 5,000 individuals estimated by BirdLife International in 2008 (BirdLife International 2011), and is most unlikely to exceed 1,000, and may be many fewer. Urgent and coordinated actions are needed to protect this species from extinction.