Data Zone
Justification of Red List category
This small shorebird has declined moderately rapidly according to recent monitoring. There is considerable uncertainty in the rate of the reduction, but it is suspected to fall between 20-29% over the past three generations and for the period projected to the near future. At present, the population size and range remain large. Due to the rate of population reduction, the species is assessed as Near Threatened.
Population justification
Breeding populations in North America are thought to total 1.56-3.21 million birds (Bart et al. in prep.). Old World populations sum to approximately 4.4 million birds (Delany et al. 2009, Nagy and Langendoen 2020, Hansen et al. 2022, Wetlands International 2023), but these data are largely collated from the species' non-breeding range and so may not all refer to mature individuals. Globally, the population is therefore estimated to number 3,000,000-7,000,000 mature individuals.
Trend justification
The overall population trend is decreasing moderately rapidly, although some populations are stable or have unknown trends. Calidris alpina is declining most rapidly in the Americas, and on the east coast, Smith et al. (2023) used migration count data to estimate a population reduction equivalent to 53.2% over three generations, although with wide confidence intervals of 18.5-73.8%. These data are also used in the Avian Conservation Assessment Database December 2023 update (Partners in Flight 2023). On the American Pacific coasts, rapid declines of 60.8% over three generations have been reported (Migratory Shorebirds Project, unpublished data), while across North America, an analysis of eBird data collected in North America between 2011 and 2021 (Fink et al. 2023) suggested congruent declines of 48% (39-52%). These data are mirrored in the sparsely available breeding data. In northern Alaska, the population size estimate of arcticola Dunlin in the Arctic National Wildlife Refuge has declined from 2002/2004 (10,506, SE = 4,112) to 2019/2022 (1,115, SE = 488); more minor declines have also been observed in the Teshekpuk Lake Special Area in north-central Alaska (2007/2008: 218 birds counted vs 2023: 198) over 53 repeat survey plots (S. Brown and R. Lanctot unpubl. data, from R. Lanctot in litt. 2024). Wintering numbers in California (pacifica) have also shown a steep decline in the past 30 years (Warnock et al. 2021) although it has been suggested that the wintering population is contracting northward (Fernandez et al. 2010).
Subspecies alpina has reportedly declined between 2000 and 2020 at a rate equivalent to c.11.5% over three generations (van Roomen et al. 2022) but in Finland breeding numbers in one study area (Kilpisjärvi; 40 km2) increased from 14 and 16 in 2005 and 2007 respectively, to 48 and 85 in 2022 and 2023 respectively, while annual standardised monitoring counts from the Hanko Bird Observatory also show short-term and long-term increases (A. Lehikoinen in litt. 2024). Subspecies arcticola (c.9% of global population) has reportedly declined very rapidly (although there is a paucity of recent data), with a population reduction between 2008 and 2014 equivalent to 97% (Weiser et al. 2020).
The trends of several other populations are less alarming. Populations of centralis and schinzii, for example, are probably stable (Nagy and Langendoen 2020, van Roomen et al. 2022), although in some European populations of schinzii declines have been reported (BirdLife International 2021); combined these two taxa represent approximately a quarter of the global population. The trends of all other populations are effectively unknown/unreported, but it is perhaps quite likely that the sizeable population in the East Asian-Australasian Flyway is declining, given the rapid declines in several other shorebirds sympatric on migration routes (where a significant number of threats are acting; IUCN 2023). Conversely, the nest density of sakhalina in the Chaun delta, Chukotka, Russia remained stable between 2011 and 2023. These uncertainties inevitably render a consolidation of data into a single global trend difficult, but weighting trends according to their population size yields a global rate of decline of at least 20% (a rate that optimistically assumes East Asian/Australasian populations are stable), thus the species is estimated to have declined by 20-29% over the past three generations. The drivers of these declines are ultimately unknown, with no direct mechanisms yet identified, for example, to be driving such rapid declines in the Americas.
Breeds from northern Alaska (USA) and northern Canada east to south-west Baffin Island. Breeds in south-east Greenland, Iceland, the Faroe Islands and northern Europe , east throughout much of Siberia to the northern Sakhalin and Kuril Islands. Birds move south for the winter, chiefly to coastlines in southern North America and northern Central America, Western Europe, north and west Africa, the Arabian Peninsula, South Asia and East Asia.
Behaviour This species is a fully migratory circumpolar breeder with several sub-populations that employ a number of migration strategies, from short coastal flights to long, non-stop flights overland on a broad front (del Hoyo et al. 1996). The sub-population that breeds in north-east Greenland migrates through Iceland, Britain and western France to arrive in its West African wintering grounds (specifically Banc d'Arguin in Mauritania) from late-July, returning again between March and early-April (del Hoyo et al. 1996). European birds may gather in large congregations from the beginning of July in areas such as the Wadden Sea or the Wash to moult (del Hoyo et al. 1996), and some juveniles may remain in the non-breeding range all year (del Hoyo et al. 1996). The species breeds dispersed or aggregated in loose colonies, and travels in group sizes of up to 1,500 on passage, remaining in large groups (up to hundreds of thousands of birds) throughout the non-breeding season (Cramp and Simmons 1977, del Hoyo et al. 1996). The species is active both diurnally and nocturnally (Cramp and Simmons 1977, del Hoyo et al. 1996, Shepherd and Lank 2004). Habitat Breeding In the breeding season this species frequents moist boggy ground interspersed with surface water, such as tussock tundra and peat-hummock tundra in the arctic, as well as wet coastal grasslands, salt marshes and wet upland moorland (Cramp and Simmons 1977, del Hoyo et al. 1996). Non-breeding In the non-breeding season this species mainly prefer estuarine mudflats, but also frequent a wide variety of freshwater and brackish wetlands (Cramp and Simmons 1977, del Hoyo et al. 1996), both coastal and inland, including lagoons, muddy freshwater shores, tidal rivers, flooded fields, sewage farms, salt-works, sandy coasts (Cramp and Simmons 1977, del Hoyo et al. 1996), lakes and dams (Hockey et al. 2005). For roosting during high tides and at night this species prefers large fields of naturally fertilised short pasture or soil-based crops with few vertical structures that could be used by predators (Shepherd and Lank 2004). Diet Breeding This species is omnivorous during the breeding season, consuming mostly adult and larval insects (dipteran flies, beetles, caddisflies, wasps, sawflies and mayflies), and also spiders, mites, earthworms, snails, slugs and plant matter (usually seeds) (Cramp and Simmons 1977, del Hoyo et al. 1996). Non-breeding It is also omnivorous during the non-breeding season, consuming mostly polychaete worms and small gastropods, as well as insects (dipteran flies and beetles), crustaceans, bivalves, plant matter and occasionally small fish (Cramp and Simmons 1977, del Hoyo et al. 1996). Breeding site Its nest is a scrape or shallow depression in the ground, concealed in vegetation and sometimes in a tuft or tussock (and thus raised slightly off the ground) (Cramp and Simmons 1977, del Hoyo et al. 1996). Management information The provision of well-surfaced paths in breeding areas that receive > 30 visitors a day has been shown to reduce the impact of human disturbance on this species' reproductive performance (Pearce-Higgins et al. 2007). It is also known to show increased hatching successes when ground predators have been excluded by erecting protective fences around nesting areas (Jackson 2001).
Numerous threats have been identified, but the extent to which any of them are driving observed declines is unknown, with much more research needed before threats can be targeted for mitigation.
Climate change has been identified for several shorebird species as a threat that is driving reduced breeding productivity by a number of mechanisms (e.g. Meltofte et al. 2007, Eikelenboom 2016, Kubelka et al. 2018); more research for this species specifically is needed. Indirect impacts of hyperabundant geese (Ross's Goose Anser rossii and Snow Goose Anser caerulescens) have been reported (Flemming et al. 2019a) including increased risk of predation (Fleming et al. 2019b), although on a broader scale densities apparently remain consistent (Flemming et al. 2019c). Elsewhere on its breeding grounds, oil drilling has been identified as a possible threat, although this is highly localised (Bart et al. in prep.).
The species is exposed to additional threats on its staging and wintering grounds, particularly habitat degradation and conversion. At Barr Al Hikman, Oman, where up to 26% of the Asian-East African Flyway population has been reported to overwinter, planned urban developments, the aquaculture (for shrimp) industry, oil refineries and disturbance from fishing industries and falcon hunting were all identified as threats by de Fouw et al. (2018) and these almost certainly apply to other important staging and wintering sites in the broader region. The extent of hunting in this region is poorly known, but shorebirds are occasionally targeted (Brochet et al. 2016). The species is threatened on the south-east coast of India (Point Calimere) by illegal hunting (bird trapping), reservoir and marshland habitat alteration by salt-industries, and habitat degradation by diminishing rainfall (changing the salt regime) (Balachandran 2006). Rapid land-use change and loss of mudflats are also major threats here. It is also threatened at Walvis Bay in Namibia, a key wetland site in southern Africa, by habitat degradation (e.g. changes in the flood regime due to road building, and wetland reclamation for suburb and port development), and disturbance from tourism (Wearne and Underhill 2005). Again, these threats are probably widespread in the region. In the Americas there is no evidence of significant pesticide poisoning, although concentrations of other contaminants have been found to be high enough to cause sub-lethal effects (reviewed in Bart et al. in prep.).
Significant numbers of C. alpina migrate down the Yellow and East China Seas where habitat loss and hunting are plausibly significant threats. The extent of reclaimed land along the Yellow Sea coastline now exceeds the extent of remaining intertidal mudflat (Murray et al. 2014, IUCN 2023), suggesting that this may have contributed greatly to declines in this species. The rate of habitat lost to land reclamation has slowed since a peak in c. 2013, in particular in recent years due to the promised near-ceasing of land reclamation in China in early 2018 (Melville 2018); however, recent satellite data suggests that the extent of intertidal mudflat has continued to decrease, in large part due to continued reclamations in the Korean Peninsula (IUCN 2023). Mudflats have also continued to degrade in suitability for this species and other shorebirds because of the invasive alien Spartina alterniflora cordgrass, which appears to be spreading; in recent (post 2020) years, this threat has probably driven greater declines than planned land reclamation. In addition to land reclamation, coastal development and a rapid increase in the human population along the coastline of the Yellow Sea has led to widespread degradation of mudflats and coastal habitats used by this species; IUCN (2023) (and references therein) cite the following as additional drivers of mudflat loss and degradation: 'processes such as changes in sediment supply, loss of coastal vegetation associated with development...erosion, redistribution of sediments due to storms, and compaction and subsidence (sinking) caused by subsurface resource and groundwater extraction are also likely to be factors'. Offshore windfarms may have a so far unquantified impact on birds due to collisions (unlikely) and displacement and disturbance of feeding birds (more likely). Disturbance on mudflats by fishermen and others using the mudflats may also be reasonably considered a threat. Hunting is also possibly a significant threat impacting this and other shorebird species on passage (Gallo-Cajiao et al. 2020).
Conservation Actions Underway
This species is covered by the general protection regime provided by Article 1 of the European Union (EU) Birds Directive to all naturally occurring wild species in the EU. It is listed on Annex II (strictly protected) of the pan-European Bern Convention, Annex II of the Convention on Migratory Species (CMS) and Annex II of the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA). Across the EU, 762 Natura 2000 sites have been designated for the conservation of this species (EEA 2024). The subspecies C. a. schinzii is listed on Annex I (special protection) of the Birds Directive, and is also listed by the Helsinki Convention (HELCOM) as a taxon that that is threatened and/or declining in the Baltic Sea. C. a. schinzii is included on the list of priority EU species that can benefit from a higher EU co-funding rate (up to 75%) under the LIFE Programme; to date (June 2024), the LIFE project database lists nine projects that have taken practical conservation measures for this subspecies, mainly in the Baltic at some of the 73 Natura 2000 sites designated for the conservation of this taxon. China is investing hundreds of millions of dollars to clear tidal mudflats of Spartina cordgrass, with the aim of eliminating 90% of it by 2025; locally, this has already been successful, for example at Chongming Dongtan National Nature Reserve (Stokstad 2023). The governments of China and South Korea have halted new projects that require or depend upon land reclamation, and across the Korean Peninsula the number of coastal wetlands has increased; moreover in China and South Korea, key areas for migratory shorebirds (including C. alpina) have been identified and prioritised by government and two World Heritage nominations have been made on these grounds (IUCN 2023). Although data on scale or impact are sparse, IUCN (2023) consider that "support for coastal wetland conservation and wise-use appears to have increased over the last decade". There has been a substantial increase in the number of volunteer groups and NGOs helping to monitor the migrations of shorebirds and other waterbirds, as well as increased media coverage and special events, demonstrating enhanced awareness among coastal communities (see also EAAFP 2016). North Korea became a Party to the Ramsar Convention and joined the EAAF Partnership in 2018. In 2021, the 'Regional Flyway Initiative' (RFI) was set up by the Asian Development Bank, with technical support from BirdLife International, with the aim of protecting and restoring priority wetland ecosystems and the associated ecosystem services they provide in the East-Asian Australasian Flyway (EAAF), the most threatened flyway globally. The Initiative is slated for implementation in 10 East, South and South-East Asian countries: Mongolia, China, Bangladesh, Viet Nam, Cambodia, Lao PDR, Philippines, Thailand, Malaysia and Indonesia, all of which are used by C. alpina on northbound and southbound migrations between breeding and wintering areas, and many also for wintering. The RFI will mobilise large-scale financing to support the protection, sustainable management and restoration of at least 50 priority wetlands across ten Asian countries, with an initial financing commitment of $3 billion from the ADB (BirdLife International 2022). Over time, the RFI aims to enhance and expand the existing efforts in conserving and managing priority wetlands identified on the basis of supporting globally significant congregations of migratory waterbirds, and leverage on collaborative opportunities with stakeholders including national governments, civil society organizations, communities, regional organisations like the East Asian-Australasian Flyway Partnership. A large portion of this species' breeding population is covered by PRISM surveys in North America, enabling regular monitoring.
Conservation Actions Proposed
Ensure population monitoring continues throughout and its range, and preferably expand it to other regions (particularly in East Asia and wintering grounds in Africa where data coverage is currently patchy). In the East Asian-Australasian Flyway, the main action needed for this is the amelioration of threats on its migration. China needs to implement its plan to eliminate 90+% of Spartina cordgrass to prevent further loss of feeding habitat (much has already been lost to land reclamation; IUCN 2023). The discharge of toxic pollutants into coastal wetlands (especially where there are large shorebird congregations) needs to be controlled. Further degradation of mudflats needs to be stopped, including monitoring and preventing detrimental release of riverine sediments and responsible planning of offshore windfarms. Tools are available, such as AviStep (https://avistep.birdlife.org/) to ensure sustainable building of renewable energy infrastructure. Many of these threats, particularly development of coastal wetlands, apply also to the Arabian Peninsula where there is a need for sensible policy-making and implementation to reduce illegal killing and habitat loss (Brochet et al. 2016, de Fouw et al. 2018).
Text account compilers
Berryman, A., Malpas, L., Ashpole, J, Ekstrom, J., Jones, V., Butchart, S.
Contributors
Dowsett, R.J., Lanctot, R. & Lehikoinen, A.
Recommended citation
BirdLife International (2024) Species factsheet: Dunlin Calidris alpina. Downloaded from
https://datazone.birdlife.org/species/factsheet/dunlin-calidris-alpina on 24/11/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 24/11/2024.