Waders (Shorebirds)
C. Zöckler1, R. Lanctot2, S. Brown3, E. Syroechkovskiy4
1UNEP World Conservation Monitoring Centre, Cambridge, UK
2U.S. Fish & Wildlife Service, Division of Migratory Bird Management, Anchorage, AK, USA
3Manomet Center for Conservation Sciences, Plymouth, MA, USA
4BirdsRussia, Moscow, Russia
February 5, 2013
Highlights
- Migratory Arctic shorebirds link virtually all corners of the World, apart from Antarctica, through their migratory routes; consequently, some populations that frequent the Arctic are affected by factors outside the Arctic.
- Waders are by far the most numerous and species rich taxa among all Arctic waterbirds and serve as good indicators of the state of global coastal and inland wetlands.
- More than 40% of arctic wader populations are declining, while only 9% are showing increasing trends.
- The African-Eurasian Flyway is the most stable of the flyways, with only 25% of the 46 populations showing declining trends. In the East Asia Australasian flyway, 100% of the 11 populations with known trends are declining, whereas in North America 56% of the 34 populations with a known trend are declining. Only 3 of the 20 populations in central Asia have trends and all are thought to be stable.
Introduction
Migratory Arctic birds fly to virtually all corners of the world, apart from Antarctica, via their migratory routes. They migrate to almost all inland and coastal wetlands, and offshore waters are often utilised by Arctic breeding waders in winter. Most Arctic waders (also known as shorebirds), spend only two to three months on the Arctic breeding grounds during the brief summer.
Across the Arctic a total of eight flyways that connect geographic areas to the south have been described (Boere & Stroud, 2006). For this comparative analysis, the three American flyways have been combined into one and the Black Sea/Mediterranean has been combined with the African Eurasian, leaving four major flyways for discussing the status and trends of waders (Fig. 4.11). Trend data are primarily from Wetlands International (2012) and supplemented by published reports from selected representative key sites in the region to provide the best information available for analyses and discussion from an Arctic and flyway perspective.
Waders are by far the most numerous and species rich taxa among all Arctic waterbirds and serve as good indicators on the state of global coastal and inland wetlands, pointing to numerous pressures mostly in the non-breeding areas. Arctic waders include 71 species and 70 separate populations amounting to almost 50 million individuals which regularly undertake long-distance migrations to all corners of the globe (Zöckler, 2012).
Flyways
The status and trend data are available for 94 populations covering >60 species of Arctic waders or 61% of the 153 populations recognised for this analysis. Of these populations over 45% are declining while 8.5% show increasing trends. Although the available data vary considerably among the flyways, the results reveal declining trends in most flyways, apart from the central Asian Flyway, although WPE5 (World Population Estimates, Fifth Edition by Wetlands International, 2012) has not established trends for many populations due to the lack of data for the entire populations (Fig. 4.11, Table 4.1). Data from the central Asia Flyway are scarce and not available for most flyway populations; however, trend data assembled from key sites in India, reflecting a significant proportion for three species (Balachandran, 2006), do not point to a similar declining picture seen in other flyways (Fig. 4.11).
African-Eurasian Flyway. For approximately 90% of the populations, trend information is available within the African-Eurasian Flyway (AEF). Considering the complexity of the flyway network sites and differing monitoring efforts across the region, continued updating of observations are encouraged. At the AEF level the results suggest that this flyway's wader populations are stable and mainly reflect European populations migrating to North Africa. Twenty-five percent of the populations are declining, which is the lowest number of declining populations compared to all other flyways.
Regular monitoring takes place at key stopover and wintering sites in the Dutch-German-Danish Wadden Sea areas (JMMB, 2011) and in the Langebaan lagoon in South Africa (Harebottle et al., 2006). Arctic waders have been monitored at these sites for over 23 years. Trends from both sites cannot be compared as they refer to different species and populations and illustrate also the difficulty in deriving reliable and accurate population estimates with mixing and shifting populations.
Trend data from 2006 for Langebaan Lagoon in South Africa are available for a period of 23 years, and show declining trends for Curlew Sandpiper, Sanderling, Turnstone, Grey Plover, Red Knot and increasing numbers for Bar-tailed Godwit and Whimbrel (Harebottle et al., 2006).
North American Flyway. In North America, there are 34 species with a total of 50 populations (Fig. 4.11). Across the North American Arctic, shorebird diversity is highest near the Bering Strait and northern Alaska, with fewer species in Canada and Greenland. Most information on population sizes of arctic shorebirds has recently been updated with information collected during the Program for Regional and International Shorebird Monitoring (PRISM) surveys (Bart and Johnston, 2012, see Arctic PRISM (Environment Canada). A first round of surveys conducted between 2001 and 2011 has provided population estimates for 26 shorebird species. The reliability of the population estimates varies by species, but will improve as remaining areas of the Arctic are surveyed and a greater understanding of habitat relationships, which are used to extrapolate densities, are developed. Based on this and other information (see Andres et al. 2012), most of the 50 populations known to breed in the North American Arctic number in the tens of thousands (29) to millions (9). A small number (12) have populations below 25,000 (Table 4.2).
Shorebird trend data come primarily from the International Shorebird Survey (ISS) and the Maritimes Shorebird Survey; both surveys began in 1974 and are focused on counting shorebirds during migration along the east coast of North America (although the ISS also has data from the Midwestern United States; Bart et al., 2007). This information, as well as species-specific information derived from breeding and wintering areas, has been consolidated by Andres et al. (2012). Long-term trends (over the last >30 years) indicate that of the 50 populations, 24 have apparent or significant declines, 13 have unknown trends, 11 are stable, 1 is increasing, and 1 is likely extinct (Table 4.2). Short-term trends (over last decade) indicate that 19 have apparent or significant declines, 16 have unknown trends, 14 are stable, and 1 is likely extinct (Table 4.2). Repeated surveys in the Arctic, as outlined in the PRISM protocols (Bart and Johnston, 2012), will provide additional information on trend data from the breeding grounds when the second round of surveys is completed.
Shorebird populations on average appear to be declining more rapidly than other bird species groups in the Canadian Arctic (Fig. 4.12). Within the shorebird group, populations have declined by 60% overall and 10 species are in severe decline (North American Bird Conservation Initiative Canada, 2012). These declines are likely due to habitat alteration at breeding, migration and wintering areas, changes in the availability of prey, increases in predators, more frequent severe weather events, hunting, pesticides and increased natural resource exploration and extraction (North American Bird Conservation Initiative Canada, 2012).
Central Asian. The situation in central Asia remains largely unknown. Trend data are available only for 3 out of 20 populations and these three were considered stable (WPE5, Wetlands International, 2012). However, long term monitoring at Point Calimere in Southern India shows strong declining trends between 1980 and 2002 for Little Stint Calidris minuta (90%), Curlew sandpiper C. ferruginea (75%) and Ruff Philomachus pugnax (90%; Balachandran, 2006). All three species also declined by 50% between 1989 and 1999 at Lake Chilika (Balachandran, 2006). Further declines have occurred in Little Stints at the same location between 2001 and 2004; the population was estimated at only 30% of the 1988 population size. In contrast, peak counts between 2001 and 2004 for Curlew sandpiper seem to indicate a recovering population (Balachandran, 2006). Because these data are from only a portion of the central Asian population and WPE5 did not establish a trend assessment for these species (Wetlands International, 2012), more monitoring is required to fully assess these and other species within the Central Asian flyway.
East Asian Australasian. Trend information for a large proportion (about 66%) of the 32 wader populations in the East Asian Australasian Flyway (EAAF) is unavailable. Of the few known population trends, all are declining. Although the flyway boasts the most species-rich complex, it has the least number of individuals. Many regions, mainly in Indonesia, Vietnam and China, remain devoid of migratory wader population data. It remains likely that the unknown populations are also declining and many recent data from Australia point to a continuing decline of many populations. Rogers & Gosbell (2006), for example, documented a long-term rapid decline in Curlew sandpipers C. ferruginea (see Figs. 4.13 and 4.14). Wilson et al. (2011) considered 22 migrant and 8 resident species with seven species of migrants to be declining significantly, and abundance of one species as significantly increasing. Declines of 43-79% in migrant abundance over 15 years were also observed. Among the declining species were ten Arctic waders, while two populations, Red-necked Stint and Sharp-tailed sandpiper, were increasing. With the exception of the Curlew sandpiper, it is not clear how representative these results are of the entire flyway.
The Far-Eastern Curlew and Great Knot have recently been classified as Vulnerable and added to the IUCN list of globally-threatened species, having experienced declines of 30-49% over the last 20-30 years (BirdLife International, 2012). Populations of Red Knots and Bar-tailed Godwits from Siberian and Alaskan breeding grounds are also declining; having lost over half of their individuals they have declined at a rate of 5-9% per year in last decade (Wilson et al., 2011). One of the key species under threat on the flyway is the Spoon-billed sandpiper (see the case study below).
The situation in the EAAF is of particular concern. The EAAF supports more migratory waterbird species and a higher proportion that is globally threatened than any other flyway in the World (MacKinnon et al., 2012; Amano et al., 2010). It also has the highest rate of loss of intertidal wetlands (as much as 50% in the last 30 years) (Barter, 2006; Yang et al., 2011) and only 5% of intertidal wetlands are protected.
Threats
Although the surveys above provide information on the status and trends of shorebirds breeding in the Arctic, they can be difficult to interpret as they often do not provide enough information to determine the mechanisms behind any declines or increases, the life stage when shorebird populations are likely to be limited (e.g., breeding, migration, non-breeding), or how climate conditions may influence recovery. To address some of these limitations, the Arctic Shorebird Demographics Network was established in 2010 to collect demographic data on shorebirds breeding in the Arctic (http://www.manomet.org/arctic-shorebird-demographics-network). The Network is composed of 14 field sites (2 in Russia, 7 in Alaska, 5 in Canada) that collect data to generate estimates of adult bird survival, nesting success, and reproductive effort. At each site environmental data that are sensitive to climate change are collected, and this information is used to help interpret changes in the demographic traits.
Although the breeding period is a very important and sensitive time for arctic waders, stressors and/or threats that occur outside the Arctic are often considered more important when trying to understand observed population trends of these global creatures.
Hunting and harvesting. Hunting of shorebirds is widespread across all major global flyways and could be a significant factor in the observed declines in all flyways (Zwarts et al., 2010; Zöckler et al., 2010a; Morrison et al., 2012; Balachandran, personal communication). Moreover, harvesting of food in critical migration feeding areas can also increase pressure on migrating populations (e.g., harvesting horseshoe crabs Limulus polyphemus in Delaware Bay, an area which reportedly sees the passage of approximately 60% of the total population of the Semipalmated Sandpiper C. pusilla during the spring migration) (Mizrahi et al., 2012).
Pollution. The use of pesticides in agricultural areas such as rice fields may affect shorebirds using those habitats directly, and drainage of pesticides into coastal areas and onto mudflats also has the potential to affect shorebirds (Morrison et al., 2012). Small-scale gold mining has increased considerably in the northern South American wintering range, and mercury, which is used in the extraction process and can reach the coast via the rivers, has the potential to affect shorebirds in coastal areas (Morrison et al., 2012). Increasing frequency and severity of hurricanes during southbound migration may be causing increased mortality during this period (Morrison et al., 2012).
Habitat loss. Major projects are developing and rapidly altering the Asian coastlines. Intertidal mudflats are disappearing at a rate of 350,000-400,000 ha /decade in the Yellow Sea, a major stop over and key moulting area for several wader species in the EAAF (Murray et al., 2011; Yang et al. 2011; Ko et al., 2011).
Case Study: Spoon-billed sandpiper
The Spoon-billed Sandpiper Eurynorhynchus pygmeus (SBS), a wader with a remarkable and unique spatulate bill, is one of the world's rarest and most unusual birds. No other bird hatches with such an adaptation and no clear scientific explanation for such a bill shape has been found. It is the significant species of the East Asian Flyway, where tens of millions of migratory waterbirds share the limited grounds with 45% of the World's human population, and is heading towards extinction perhaps faster than any other bird species on Earth (Syroechkovskiy, 2005). It declined by more than 90% over the last 30 years and is now critically endangered. A realistic risk of extinction in 15-20 years has been predicted by modeling, when recent trends obtained mainly in Arctic breeding areas were projected into the future (Zöckler et al., 2010b). Recent population estimates of about 100 breeding pairs are based on evaluations in the intensively-studied breeding grounds. Of the 42 known main breeding locations, 28 were revisited in the last twelve years: 18 breeding population were extinct and ten populations showed extreme declines in numbers; no stable or increasing populations were discovered. In past five years, one key breeding population became extinct and another key population is considered nearly extinct. Only one breeding population seems to be stable, although on very low levels of about 20-30 breeding pairs only around Meinypilgyno, Chuktoka (Syroechkovskiy et al., unpublished).
Breeding on coastal tundra in Chukotka (Russian Far East) and wintering 5,000 km away on the tropical coasts of China and south-east Asia, the spoon-billed sandpiper faces many threats. The main threats are: (1) habitat reclamation in the non-breeding grounds, such as inter-tidal areas of East Asia for farming and development; (2) subsistence hunting pressure in Myanmar, Bangladesh and some other wintering grounds; and (3) very low breeding productivity in Chukotka. The situation is particularly difficult in China, where around 50% of intertidal areas are reclaimed, development is increasing and there is little conservation action. Spoon-billed sandpipers and millions of other waterbirds depend on large tidal areas, such as the Saemangeum in South Korea, to rest and refuel on migration. This reclamation project, reported to be the largest in the World, has added seriously to the decline of the species.
A project focusing on the conservation of the species started in 2000 in Russia. The effort focuses on the following activities: (1) conservation action to mitigate threats in wintering grounds in Myanmar, Bangladesh, Thailand, China and Vietnam; (2) inventories in the non-breeding range to discover remaining key sites; (3) captive breeding program led by WWT, with the goal of establishing the first ever captive population at Slimbridge, UK, so as to allow the re-introduction of the species to the Russian breeding grounds should the wild populations continue to decline; (4) "head starting", a project aimed at increasing the number of juveniles produced at the key breeding site in Chukotka, which holds around 30% of the world population (this involves taking eggs from incubating birds and raising chicks to fledging age at Meinopylgino, before releasing them back into the wild); (5) monitoring and guarding key breeding sites as well as further research on breeding ecology; and (6) advocacy and awareness work along the whole flyway, with particular focus on governments and local communities.
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