BIOLOGICAL CONSERVATION 141 (2008) 2301– 2309
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New Anatidae population estimates for eastern China: Implications for current flyway estimates
Lei Caoa,*, Mark Barterb, Gang Leic aSchool of Life Sciences, University of Science and Technology of China, No. 96 Jinzhai Road, Hefei 230026, Anhui, China b21 Chivalry Avenue, Glen Waverley, Victoria 3150, Australia cWWF China, Room 607, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, 340 Xudong Road, Wuchang 43007, Hubei Province, China
ARTICLE INFO ABSTRACT
Article history: Soundly-based conservation plans for Anatidae require abundance and distributional data Received 10 January 2008 to provide accurate estimation of population sizes and trends and to identify key sites for Received in revised form protection. Here, we report the first ever extensive surveys throughout eastern China’s wet- 24 June 2008 lands for Anatidae, 80% of which occurred in the Yangtze floodplain. Population estimates Accepted 28 June 2008 for 24 species with sufficient data are provided, allowing assessment of the accuracy of cur- Available online 9 August 2008 rent flyway population estimates; fourteen species are far less numerous than previously believed and three far more numerous. Further improvement of the population estimates Keywords: for eastern China will need coordinated counts across the region requiring a large, skilled Anatidae counter network. China 2008 Elsevier Ltd. All rights reserved. East Asia Population estimate Yangtze
1. Introduction declines result from habitat loss and hunting on the staging and non-breeding areas (Syroechkovskiy, 2006). Evidence for Anatidae populations are being adversely affected worldwide declines in eastern China’s Anatidae populations comes by wetland habitat degradation and loss (Wetlands mostly from the Russian breeding and staging sites International, 2006). This is particularly critical in eastern (Rogacheva, 1992; Melnikov, 2000; Poyarkov, 2001; Syroechkov- China, where rapid economic development since the early skiy, 2006) and, to a lesser extent, from Chinese studies in the 1980s has caused land claim, pollution and human distur- non-breeding areas (Hu and Cui, 1990; Lu, 1996; Cao et al., bance in coastal and inland wetlands (Lu, 1996; State Forestry 2008). Breeding populations of greater white-fronted goose Administration, 2002; He and Zhang, 2001), which have his- (Anser albifrons) and bean goose (Anser fabalis) migrating to torically supported large numbers of a diverse range of China have declined by about 80% and 65%, respectively, since Anatidae species during the non-breeding period (Callaghan the mid-1980s (Syroechkovskiy, 2006). Ten of the thirteen and Harshman, 2005; Wetlands International, 2006). migratory populations of dabbling ducks and six of the four- Eastern China’s Anatidae mainly breed in northern China, teen populations of diving ducks have also decreased in abun- Mongolia, and central and eastern Siberia (Wetlands dance (E. Syroechkovskiy Jr. in litt.). International, 2006), where low human population densities Pressures on eastern China’s wetlands can be expected to result in few pressures; it is most likely that population intensify as declining and controlled river flows (from water
* Corresponding author: Tel.: +86 1396 6714569; fax: +86 551 3601443. E-mail addresses: [email protected] (L. Cao), [email protected] (M. Barter), [email protected] (G. Lei). 0006-3207/$ - see front matter 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2008.06.022 2302 BIOLOGICAL CONSERVATION 141 (2008) 2301– 2309
extraction and damming) increasingly affect seasonal water culture ponds and salt pans are widespread (pers. obs.). The levels of inland lakes and sediment and nutrient inputs to moderating influence of the sea on air temperatures means both inland and coastal wetlands, thus affecting biological that the much of the coastal areas immediately north of the productivity (UNEP, 2005; Wang, 2006; Li et al., 2007). Acceler- average January 0 C isotherm remain unfrozen and can be ating coastal land claim (Barter, 2002; pers. obs.) and reducing used by Anatidae during the winter months; however, most accretion rates (Yang et al., 2007) will also affect future inter- of the northern Bo Sea and Korea Bay coasts are frozen at this tidal habitat extent. time and unsuitable for Anatidae (Lanzhou Institute of To ensure the survival and future recovery of eastern Glaciology and Geocryology, 1988). China’s Anatidae populations, effective conservation plans Relatively few Anatidae are likely to occur to the west of need to be developed based on accurate knowledge of the dis- 110 E during the non-breeding season, as this part of China tribution, size and status of individual populations. Existing is mostly highly elevated, containing limited suitable habitat, data for the region are temporally and spatially limited and much of it lies well to the north of the average January (Perennou et al., 1994; Lopez and Mundkur, 1997; Li and 0 C isotherm. Mundkur, 2004, 2007), and unsuitable for estimating popula- tion sizes and trends or identifying key sites for inclusion in 2.2. Survey methodology the Protected Area system. In response to this pressing need for up-to-date, systematically-collected abundance and distri- We used the ‘‘look-see’’ counting method (Bibby et al., 2000; bution data we initiated new waterbird surveys in eastern Delany, 2005a,b), which has been commonly employed to cen- China. These were conducted first in the Yangtze floodplain, sus waterbirds in large wetland complexes (e.g. Wadden Sea: the most important waterbird region in eastern China and Meltofte et al., 1994; Asia: Li and Mundkur, 2007). The objec- threatened by downstream hydrological changes from the tive of our surveys was to identify and count all Anatidae Three Gorges Dam (BirdLife International, 2003). Surveys of (and other waterbirds) present in a wetland; most Anatidae the majority of the other key wetland areas in eastern China gather in visible, often large, flocks during the non-breeding followed to provide the first comprehensive regional waterbird season making them easy to locate and count. Surveys were dataset for the non-breeding season, filling an important gap conducted during the 2002/03–2006/07 non-breeding seasons: in knowledge of the abundance and distributions of northern the Yangtze floodplain was surveyed in 2002/03, 2003/04 and hemisphere Anatidae. 2004/05 (Barter and Lei, 2003; Barter et al., 2005, 2006), the This paper provides new population estimates for Huai River floodplain (unpub. data) and the coasts of Anatidae species occurring in eastern China and discusses Shandong, Jiangsu, Zhejiang (unpub. data) and Fujian (Barter the implications of these for current flyway estimates. A et al., 2007) were covered in 2005/06 and 2006/07 (Fig. 1); all planned companion paper will focus on Anatidae distribu- surveys were carried out in the late-January/February period, tion, key sites and conservation status. except those of the Jiangsu coast and Huai River floodplain Waterbird Population Estimates Fourth Edition (Wetlands which took place during mid-November to early-December. International, 2006) has been used as the source for common Surveys took from 5 to 20 days to complete, and it is esti- and scientific names, core non-breeding ranges and popula- mated that total linear lengths of approximately of 2500 km tion estimates. of inland waterways and 3500 km of coastline were covered. We used geo-referenced satellite images, often in combi- 2. Methods nation with advice from local people, to locate wetlands. Count sites were selected that enabled as much as possible 2.1. Study area and habitat availability of each wetland to be satisfactorily covered; normally these sites were 3–4 km apart (since birds could be identified and In inland areas of eastern China (defined here as east of 110 E), counted at distances up to 2 km), but less under conditions suitable Anatidae non-breeding habitat is mainly confined to of poor visibility. Access to wetlands in China is often chal- the central part; most of the south (i.e. the region between lenging due to lack of topographic maps and we relied heavily the Yangtze River and the coast) is elevated and provides little on GPS units with pre-entered site coordinates to reach count wetland habitat, whilst the north is too cold during winter. positions; GPS track logs were also recorded so that we could The most important regions occur along the floodplains of check how well the wetland had been surveyed and calculate the Yangtze and Huai Rivers (Fig. 1), where falling water levels the coverage achieved. We are confident that our methods en- during the autumn and winter provide suitable non-breeding abled us to identify the great majority of the key Anatidae- habitat for a wide range of Anatidae species. The Yellow River supporting wetlands in the survey regions and to cover them wetlands are of less importance due to lack of water (Zhu as completely as possible. One type of habitat that we were et al., 2003); they also lie north of the average January 0 C unable to survey adequately comprised the numerous reser- isotherm (Liu, 1997) and are consequently often frozen during voirs, but we believe these were unlikely to support large much of the non-breeding season. numbers of Anatidae (see Section 4). Along the coast there is much suitable Anatidae habitat. There are very extensive intertidal areas in the Yellow and 2.3. Data collection and organisation Bo Seas, and Korea Bay, often consisting of long stretches of continuous mudflat, and numerous bays and estuaries with Species counts and coordinates were recorded for each site, large mudflats in the East China and South China Seas (Wang together with information on survey conditions (e.g. weather, et al., 2002); sub-coastal wetlands mainly comprising aqua- visibility, accessibility, count problems). Databases were BIOLOGICAL CONSERVATION 141 (2008) 2301– 2309 2303
Fig. 1 – Eastern China, showing geographical locations referred to in the text, survey regions and average January 0 C isotherm. compiled for each species and these were augmented with 37%, based on their analysis of large scale counts in the Dutch data from other sources, particularly for areas not covered Wadden Sea. We have selected a general detection rate of by our surveys (China Ornithological Society, 2004, 2005, 80%, as this is more likely to result in a conservative popula- 2006, 2007; Hong Kong Bird Watching Society, 2007; Zhang tion estimate rather than an overestimate; however for the and Ma, 2007; H.Y. Yang, in litt.). larger, more visible, species (i.e. swans, geese and shelducks) we have assumed a detection rate of 100%. 2.4. Assumptions We calculated that the overall survey coverage achieved for coastal areas was 75% using data on provincial intertidal In deriving the population estimates, we have assumed that areas (China State Environmental Protection Administration, abundances and distributions of Anatidae in the different 2006) and our estimates of the percentage of this habitat sur- Provinces and Regions did not vary: (1) between years, (2) dur- veyed in each province. Similarly, we arrived at a coverage of ing the annual survey period (mid-November to February), 78% for the inland region using data on inland wetland areas and (3) during the time that a particular Province or Region (State Forestry Administration, 2002). The main prospective was surveyed. The impact of these assumptions on the popu- areas not surveyed were coastal Guangdong, the western part lation estimates is assessed in Section 4. of the Bo Sea and wetlands along the Yellow River. Given the similarity of coverages for the two habitat types and the desir- 2.5. Population estimates for eastern China ability of employing a conservative value for estimation of population sizes, we chose to use a general factor of 80% for Species population estimates were derived from the raw the percentage of total Anatidae habitat surveyed. counts (i.e. total of individuals actually counted) by adjusting Thus, as an example, the Spot-billed Duck (Anas poe- for the estimated: cilorhyncha) raw count of 47,881 (average wetland counts were used when available) was adjusted to 64,907, when survey • Coverages achieved of the individual wetlands visited coverages of the individual wetlands at which the species oc- (average = 72%; SD = 22%; n = 153; range 30–100%); we have curred were taken into account. This figure has been further assumed that Anatidae densities were the same in both adjusted to 81,134 to allow for missed birds (64,907/0.8) and counted and uncounted areas within a wetland, again to 101,417 to allow for the estimated 20% of inland • detection rates for the different species (80% or 100% and coastal habitats not covered by the surveys (81 134/0.8). depending on species, see below); and, Finally, all estimates were rounded to two significant figures, • percentage of the total suitable Anatidae habitat surveyed i.e. 100,000 in this example. in eastern China (estimated as 80%, see below). 2.6. Estimation of flyway population sizes and Birds can be missed during a count for a variety of reasons comparison with current estimates (e.g. hidden by vegetation, cryptic appearance, poor visibility, counter inexperience). Rappoldt et al. (1985) believed that the The core non-breeding area for most species lies within systematic error caused by missing birds is unlikely to exceed East Asia, i.e. mainland China, Taiwan, South Korea and 2304 BIOLOGICAL CONSERVATION 141 (2008) 2301– 2309
Table 1 – Raw count data and population estimates for 24 Anatidae species in eastern China; population estimates were obtained by adjusting the raw counts (i.e. total of individuals actually counted) to allow for estimated wetland coverage, habitat coverage and detection rates Raw count Population estimate
Mute swan (Cygnus olor) 501 630 Whooper swan (Cygnus cygnus) 3091 3900 Tundra swan (Cygnus columbianus) 65,142 81,000 Swan goose (Anser cygnoides) 62,507 78,000 Bean goose (Anser fabalis) 119,766 150,000 Greater white-fronted goose (Anser albifrons) 26,544 33,000 Lesser white-fronted goose (Anser erythropus) 16,956 21,000 Greylag goose (Anser anser) 6203 13,000 Ruddy shelduck (Tadorna ferruginea) 3578 5,500 Common shelduck (Tadorna tadorna) 12,049 18,000 Eurasian wigeon (Anas penelope) 24,141 50,000 Falcated duck (Anas falcata) 39,877 78,000 Gadwall (Anas strepera) 3762 7700 Baikal teal (Anas formosa) 58,081 91,000 Common teal (Anas crecca) 67,411 146,000 Northern mallard (Anas platyrhynchos) 34,954 73,000 Spot-billed duck (Anas poecilorhyncha) 47,881 100,000 Northern pintail (Anas acuta) 21,704 46,000 Northern shoveler (Anas clypeata) 14,969 27,000 Common pochard (Aythya ferina) 10,222 18,000 Baer’s pochard (Aythya baeri) 335 850 Tufted duck (Aythya fuligula) 5533 11,000 Smew (Mergellus albellus) 9087 15,000 Goosander (Mergus merganser) 17,374 29,000
Total 671,668 1,098,780
Japan (Wetlands International, 2006). Thus, in estimating Satisfactory habitat coverage enabled population esti- population sizes for mainland China some allowance mates to be made for 24 of the 35 species of Anatidae encoun- should be made for those species whose populations occur tered during the five-year survey period (Table 1). Of the other to the west of 110 E. However, few data from this region 11 species, insufficient coverages were achieved of the pre- are available for most species and, as the additional num- ferred habitats of the riverine ducks: mandarin duck (Aix gale- ber of each is likely to be small due to lack of suitable hab- riculata) and scaly-sided merganser (Mergus squamatus), and itat and cold weather, we have used the eastern China the marine ducks: greater scaup (Aythya marila), common sco- estimates as a proxy for mainland China; the only excep- ter (Melanitta nigra), velvet scoter (Melanitta fusca), common tions are for the mute swan (Cygnus olor) and whooper goldeneye (Bucephala clangula) and red-breasted merganser swan (Cygnus cygnus) for which a large part, of known size, (Mergus serrator), to allow realistic population estimates to of their non-breeding populations occurs in western China be made for these species; the bar-headed goose (Anser indi- (Ma and Cai, 2000) at sites where springs maintain small cus), red-breasted goose (Branta ruficollis) and ferruginous duck unfrozen areas during winter; few other Anatidae are re- (Aythya nyroca) are vagrants in eastern China, and the ported to occur in the region during this period (Scott, garganey (Anas querquedula) is mainly a summer visitor and 1989; Ma and Cai, 2000; Anon, 2001). is uncommon in eastern China during the non-breeding sea- To obtain flyway population estimates for those species son (Wetlands International, 2006). whose core non-breeding area lies within East Asia, the China estimate has been combined with average counts (five year 3. Results averages: 2000–2004) for Japan, South Korea and Taiwan; cov- erage and count results for these three countries were consid- 3.1. Anatidae distribution ered to be generally very good (Li and Mundkur, 2004, 2007). The estimates were compared with those published in Wet- Major Anatidae concentrations occurred in the Yangtze flood- lands International (2006) to determine whether there were plain (about 80% of the total count) and, to a lesser extent, any major differences. north of the Yangtze estuary along the Jiangsu coast and in Where species ranges extended into southeast Asia, pub- the Bo Sea; relatively small numbers are present on the lished count data from the relevant range countries (Li and south-eastern coast (Fig. 2). Mundkur, 2004, 2007) were used to help in assessing the accu- racy of current flyway population estimates; however, the 3.2. Population estimates for eastern China coverage and count data for a number of these countries are not considered to be as good as in East Asia (Li and Mundkur, The population estimates for the 24 species for which satis- 2004, 2007). factory habitat coverage was achieved are given in Table 1. BIOLOGICAL CONSERVATION 141 (2008) 2301– 2309 2305
Fig. 2 – Distribution of Anatidae in eastern China, showing locations of the 153 wetlands at which Anatidae were found during the winters of 2002/03–2006/07 and numbers recorded at each wetland.
The raw counts are included to provide an indication of the population which is more than twice as high as the current extrapolation ratios employed in obtaining the estimates; estimate. these average about 1.6:1, based on the total estimated popu- Species whose ranges extend beyond East Asia, but for lation of about 1.1 million for the 24 species. which current estimates are probably too high, are common teal (Anas crecca), spot-billed duck (ssp. zonorhyncha), northern 3.3. Flyway population estimates shoveler (Anas clypeata), Baer’s Pochard (Aythya baeri) and tufted duck (Aythya fuligula). The ranges of common teal, The calculated species totals for East Asia and current esti- northern shoveler and tufted duck include both East Asia mates of the relevant flyway populations are given in Table and Southeast Asia. The maximum annual numbers recorded 2. The table contains data for 22 of the 24 species listed in for the three species during the 2001–2004 period in Southeast Table 1; greylag goose (Anser anser) and ruddy shelduck Asia were approximately 1800 common teal, 3300 northern (Tadorna ferruginea) have been omitted because only a minor shoveler and 17,600 tufted duck. Even allowing for the proba- part of their flyway populations occurs in eastern China. bility of major undercounting occurring in some countries (Li The flyway populations of 15 of the Anatidae species and Mundkur, 2004, 2007) it seems very unlikely that the listed in Table 2 (i.e. those above the line) only occur in East numbers of these three species in Southeast Asia are large en- Asia (Wetlands International, 2006) and the calculated East ough to make up the shortfalls, i.e. >400,000 for common teal Asian population totals for these species can be directly and northern shoveler, and 140,000 for tufted duck. The range compared with the current estimates for their flyway popu- of the spot-billed duck subspecies occurring in eastern China lations. The populations of the other seven species have lar- (zonorhyncha) extends to southern China, but it seems very ger ranges and it is necessary to take into account the improbable that this region could be supporting the ‘‘missing’’ numbers occurring outside East Asia when comparing pop- 800,000 birds. The Baer’s pochard has a wide range extending ulation estimates. from Japan westwards to southern China, southeast Asia, The calculated population totals for East Asia are much northeast India and Bangladesh (Wetlands international, lower (defined as 675% of the current flyway estimate; mid- 2006); data from the western part of the range indicates that point used if range given) than the flyway estimates for nine it is scarce there also (see Section 4) and it seems probable of the species with populations confined to East Asia, i.e. for that the actual population size is much lower than the current mute swan, whooper swan, greater white-fronted goose, estimate. common shelduck (Tadorna tadorna), eurasian wigeon (Anas Estimated bean goose numbers are much higher than the penelope), gadwall (Anas strepera), northern mallard (Anas combined current estimates for the middendorfi and serrirostris platyrhynchos), smew (Mergellus albellus) and goosander (Mer- subspecies but, as very little is known about the distributions gus merganser). On the other hand, the falcated duck (Anas fal- of the subspecies, it is impossible to determine whether one cata) is present in much higher numbers (defined as P125% of subspecies or both have higher populations than currently the current flyway estimate) having an estimated East Asia estimated. 2306 BIOLOGICAL CONSERVATION 141 (2008) 2301– 2309
Table 2 – Comparison of the totals for East Asia (China, Taiwan, South Korea and Japan) with current flyway estimates; the relevant populations of the 15 species above the line occur within East Asia, whilst the remaining seven species have larger ranges Chinaa Taiwanb South Japanb East Asiac %d Estimated flyway %f Koreab population population e
Mute swan 830 29 177 1000 83 1000–3000 50 Whooper swan 5900 3589 29,546 39,000 15 60,000 65 Tundra swan 81,000 259 30,350 110,000 74 92,000 120 Swan goose 78,000 2 18 2 78,000 100 60,000–100,000 98 Greater white-fronted goose 33,000 6 30,275 69,732 130,000 25 150,000–200,000 74 Lesser white-fronted goose 21,000 2 2 6 21,000 100 20,000 105 Common shelduck 18,000 6 32,542 700 51,000 35 100,000–150,000 41 Eurasian wigeon 50,000 2186 6571 182,379 240,000 21 500,000–1,000,000 32 Falcated duck 78,000 20 1936 9180 89,000 88 35,000 254 Gadwall 7700 60 4259 17,895 30,000 26 500,000–1,000,000 4 Baikal teal 91,000 2 400,000g 2650 490,000 19 500,000 98 Northern mallard 73,000 140 289,867 451,705 810,000 9 1,500,000 54 Common pochard 18,000 22 34,171 174,761 230,000 8 300,000 77 Smew 15,000 771 2026 18,000 83 25,000 72
Goosander 29,000 6037 4406 39,000 74 50,000–100,000 52 Bean goose 150,000 3 31,892 10,743 190,000 79 80,000/70,000h 127 Common teal 146,000 20,607 17,626 179,772 360,000 41 600,000–1,000,000 45 Spot-billed duck 100,000 1051 85,838 206,393 390,000 26 800,000–1,600,000 33 Northern pintail 46,000 1595 22,365 175,767 250,000 18 200,000–300,000 100 Northern shoveler 27,000 2287 2940 15,584 48,000 56 500,000 10 Baer’s pochard 850 2 1 850 100 10,000–20,000 6 Tufted duck 11,000 1443 5343 90,631 110,000 10 200,000–300,000 44 a Estimates from this study. b Averages of 2000–2004 annual winter counts (Li and Mundkur, 2004, 2007). c Sum of China, Taiwan, South Korea and Japan, rounded to two significant figures. d Percentage that the estimated China population comprises of the calculated East Asia population. e Current flyway population estimates (Wetlands International, 2006). f Percentage that the calculated East Asia population comprises of the current estimated flyway population (mid-point used for range). g Moores (2005). h Bean Goose consists of two populations (middendorfi: 80,000; serrirostris: 70,000).
4. Discussion 4.1. Impact of assumptions on population estimates
Despite serious, and ongoing, degradation and loss of habi- The great majority of Anatidae (80%) were located in the tats, eastern China’s extensive wetlands are still of great Yangtze floodplain and the count methodology in this region importance for Anatidae during the non-breeding season can be expected to have a large effect on the accuracy of the when it is estimated that the region supports in excess of overall population estimates. The impact on population esti- one million birds; the high regional diversity reported by mates of annual variations in breeding productivity and dis- Callaghan and Harshman (2005) was confirmed with 35 spe- tributional changes between years will be reduced because cies being found during the five-year survey period. counts for individual wetlands in this region were averaged. Eastern China is the most important region within East As the three Yangtze floodplain surveys were all conducted Asia for mute and tundra swans, and swan goose (Anser in the January–February period, errors due to seasonal move- cygnoides), lesser white-fronted goose (Anser erythropus) and ments will be minimised and, additionally, because of the bean goose; it also supports large proportions (i.e. >20% of short period during which surveys were conducted (maxi- their flyway populations) of the calculated East Asian popula- mum of twenty days), it was unlikely that significant move- tions of 10 duck species: common shelduck, eurasian wigeon, ments will have occurred within the region during this time. falcated duck, gadwall, common teal, spot-billed duck, Thus, we are confident that the Yangtze floodplain portion northern shoveler, Baer’s pochard, smew and goosander. of the individual population estimates is reasonably accurate. The region is particularly important for three globally Although we had to rely on count data from single surveys threatened species (BirdLife International, 2001): supporting in the coastal areas and, thus, estimation errors could arise the entire global population of the swan goose (vulnerable), from inter- and intra-year movements, the impact will be the entire flyway population and 65% of the global population reduced as these areas only supported 20% of the total of the lesser white-fronted goose (vulnerable), and approxi- Anatidae population. Additionally, coastal surveys were con- mately 90% of the newly estimated falcated duck (near threa- ducted over short periods (i.e. 8–20 days) and distributional tened) global population. changes were unlikely to be great during the survey periods. BIOLOGICAL CONSERVATION 141 (2008) 2301– 2309 2307
The major cause of large scale movements during winter that large declines in numbers and ranges have occurred for will probably be due to cold weather (e.g. Ridgill and Fox, many Anatidae species (Cao et al., 2008). Whilst declines 1990), but we believe that these were unlikely to have occurred can be mostly attributed to habitat loss and human distur- during 2002/03–2006/07 as average January temperatures bance, it is possible that global warming is causing changes (China Statistical Yearbooks, 2004–2007) during this period for in wintering distributions; this could explain why the greater two cities in the northern part of eastern China, representative white-fronted goose is now occurring in higher numbers in of the region from where Anatidae would be forced south by South Korea than previously (Syroechkovskiy, 2006), possibly cold weather (i.e. Tianjin, on the coast, Zhengzhou, inland on leading to a reduction in numbers wintering in eastern China. the Yellow River; Fig. 1), ranged from 0.0 to 1.5 C above long As a consequence of the large differences between the term averages (1961–1990) (Kaiser et al., 1991), except in 2005 new and current estimates, there is a need to critically review when they were 0.3 C and 0.5 C colder, respectively. the current flyway population estimates for mute swan, Whilst we believe that counts were not greatly affected by whooper swan, greater white-fronted goose, common shel- inter- or intra-year movements, it is important to note that duck, eurasian wigeon, gadwall, common teal, northern mal- the validity of the assumptions cannot currently be assessed lard, spot-billed duck, northern shoveler, Baer’s pochard, from available information and the variation in annual and tufted duck, smew and goosander, for which current seasonal numbers at most wetlands is unknown. estimates appear to be too high, and for the bean goose and falcated duck, for which they seem to be too low. 4.2. Impact of count errors on population estimates Syroechkovskiy (2002) estimated that the number of tun- dra swans on the Russian breeding grounds in the late Each count will have a stochastic error but, as the raw count 1990s was about 66,400, of which approximately 30,000 win- totals for individual species were made up of many separate tered in Europe and Central Asia and 10,000+ in China; our counts, the errors will tend to cancel each other out. However, estimates of 110,000 for East Asia and 81,000 for China greatly systematic errors can be large and the tendency for counters exceed the suggested total breeding population and Chinese- to underestimate flock sizes increases as these get larger wintering numbers. It is important to reassess numbers on (Prater, 1979); also, inexperienced counters are more likely the breeding grounds and at staging sites to resolve the dis- to underestimate flock sizes (Erwin, 1982). The choice of a crepancies in estimates and to identify the breeding locations detection rate of 80% for all except the large Anatidae is prob- of Chinese-wintering tundra swans. ably optimistic, as Meltofte et al. (1994) report that in synchro- The status of the endangered Baer’s pochard (BirdLife nized ground and aerial counts in the Danish Wadden Sea the International, 2001) is of considerable concern. As a result of ground counts contributed 50–67% of the total count, with the reports of low numbers in the Yangtze floodplain (Barter aerial counts providing the remainder. The impact of flock et al., 2005, 2006), information was sought on the status of size underestimation and an optimistic detection rate means the species elsewhere in the range and comment received that our population estimates are likely to be conservative. from China, Thailand, North Korea, South Korea, Bangladesh, It is possible that our estimates of goose numbers are low, Laos, Vietnam, Nepal and Myanmar indicated that the species as birds may have been foraging outside the wetland whilst a is rare almost everywhere and has declined greatly in recent survey was being conducted (Lu and Zhang, 1996). However, years (BirdLife International, 2007). The largest concentra- during the surveys we passed through very extensive areas tions appear to be present in Myanmar, where numbers seem of fallow rice paddies and agricultural fields with apparently to be stable (about 650 birds) at the main site (BirdLife suitable forage but very rarely saw geese feeding and our International, 2007). The current global population estimate impression was that most geese feed within, or adjacent to, is 10,000–20,000, but it seems that the actual population is wetlands and, therefore, the majority would have been probably now less than 5000. counted. However, it is important to determine the foraging and roosting strategies of geese in eastern China and, if nec- 4.4. Reservoirs essary, modify survey techniques to ensure that accurate counts are achieved. For logistical reasons we were unable to satisfactorily cover the very numerous reservoirs; fifteen low-lying reservoirs 4.3. Need for reviews of current estimates were visited on an ad-hoc basis in Shandong, Jiangsu and Anhui and these averaged 226 birds each, with 49% of the to- The new species population estimates for China are often tal count being common teal and 29% northern mallard; how- much lower than previous estimates (Miyabayashi and ever, we found very few Anatidae when we visited c.250 Mundkur, 1999), but it would be misleading to compare these reservoirs along dammed rivers in elevated regions of Anhui, data to estimate the size of population trends, as the earlier Jiangxi, Fujian and Guangdong during surveys for Scaly-sided estimates were mostly based on incomplete data and the pop- Mergansers in the 2005/06 and 2007/08 winters (unpublished ulation estimates for many species were probably too high. data). There are reportedly 85,000 reservoirs in China (Xinhua, However, there is little doubt that population sizes have de- 2007), the majority of which are presumably located in the clined greatly since the 1950s (Hu and Cui, 1990), Lu (1996) east where most of the human population, and agricultural estimated Anatidae numbers in China in the early 1990s to and industrial activity occurs; most reservoirs are sited in ele- be 3–4 million, whereas the recent surveys resulted in an esti- vated areas and, therefore, are unlikely to contain many mate of about 1.1 million; a recent comparison of historical Anatidae. However, it is important to determine the overall and contemporary data from eastern China also indicates value of reservoirs as Anatidae habitat; a stratified sampling 2308 BIOLOGICAL CONSERVATION 141 (2008) 2301– 2309
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