While Pluvialis squatarola remains a widespread and abundant species it is listed as Vulnerable in response to increasing evidence for rapid population declines over the past three generations (23 years), estimated to be more than 30%. The exact causes of these declines are unknown, but a myriad of plausible threats have been identified including habitat loss and degradation, disturbance and hunting.

Breeds in Arctic Russia from the Kanin Peninsula to Chukotskiy and Anadyrskaya, and Alaska, USA, to Melville Peninsula and Baffin Island (Canada). Birds winter widely on coastlines of North and South America, Europe, Africa, South Asia, South-East Asia and Australasia, with birds occurring in virtually every country when on migration.

Spans all major flyways with a vast breeding range that covers much of Arctic Russia and the Nearctic.
Breeding populations in western Siberia winter in Western Europe and West Africa where estimated to number c.200,000 (von Roomen et al. 2014, Nagy and Langendoen 2020). Numbers wintering in south-west Asia and eastern Africa less certain, but suspected to be c.90,000 (Wetlands International 2012). An additional 30,000 suspected to winter in South Asia (Wetlands International 2012). Numbers in the East Asian-Australasian Flyway estimated at c.80,000 in 2016 (Hansen et al. 2023). The total number breeding in Siberia is therefore estimated to be c.240,000-280,000, assuming not all of the estimates discussed previously, which are made from non-breeding areas, refer to mature individuals (which are assumed to make up 60-70% of the population).

Larger numbers breed in the Nearctic. Andres et al. (2012) previously estimated 262,700 across Alaska and Arctic Canada, however this noted that the estimate would increase as the PRISM surveys were incomplete. A draft status review of shorebirds reports a final PRISM estimate of at least 1 million birds, based on c.725,000 (353,000-1,100,000) in Arctic Canada (Bart et al. in prep.) and an additional c.260,000 from Alaska, but the latter covers only a proportion of the species' Alaskan breeding range, and the number in Alaska may be closer to that from Arctic Canada. Accordingly, the number of birds in the Nearctic is estimated at c.1,000,000-2,000,000, most of which are probably mature individuals given they are from breeding season surveys.

Combining estimates yields a total population of c.1,250,000-2,250,000 mature individuals. The total population estimate used here is a broader bracket of 1,000,000-2,500,000 mature individuals, acknowledging that there are several elements of uncertainty, including the extent to which populations have declined since population estimates were made, and the possibility that the Siberian population may be underestimated.

Behaviour This species is fully migratory (del Hoyo et al. 1996). It departs its breeding grounds from late-July to September (southward movements continuing into November) and returns from late-May to June (Hayman et al. 1986, del Hoyo et al. 1996). It breeds from May to August in solitary well-dispersed pairs and forages alone or in small loose flocks of up to 30 individuals (Johnsgard 1981, Hayman et al. 1986, del Hoyo et al. 1996). It is gregarious during the winter however, often roosting in large flocks containing up to several thousand individuals (del Hoyo et al. 1996). 

Habitat Breeding The species nests in the high Arctic in both upland and valley locations between the treeline and the coast, utilising dry stony tundra with sedge, moss, lichen, grass or dwarf birch, peat ridges in tundra marshes, dry exposed ridges, riverbanks, raised sand or gravel beaches, and rocky slopes (Johnsgard 1981, del Hoyo et al. 1996, Snow and Perrins 1998). Non-breeding Outside of the breeding season the species frequents intertidal mudflats, saltmarshes, sandflats and beaches of oceanic coastlines, bays and estuaries (Johnsgard 1981, del Hoyo et al. 1996). During migration it may also be found inland on lakes, pools or grasslands (del Hoyo et al. 1996). 

Diet Breeding During the breeding season the diet of this species consists largely of adult and larval insects such as beetles and Diptera as well as some plant matter (e.g. grass seeds and stems) (del Hoyo et al. 1996). Non-breeding When on the coast in its wintering range the species takes marine polychaete worms, molluscs and crustaceans (e.g. crabs, sand shrimps), occasionally also taking insects (e.g. grasshoppers and beetles) or earthworms when in inland habitats on passage (Johnsgard 1981, del Hoyo et al. 1996). 

Breeding site The nest is a shallow scrape on dry ground in exposed, stony sites, neighbouring nests not less than 400 m apart (del Hoyo et al. 1996, Snow and Perrins 1998). 

Management information In the UK there is evidence that the removal of Common Cordgrass (Spartina anglica) from tidal mudflats using a herbicide is beneficial for the species (Evans 1986).

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. Available breeding habitat based on predicted distribution under future climate change scenarios is predicted to reduce by between 82% (RCP 4.5) and 87% (RCP 8.5) by 2070 (Wauchope et al. 2017).

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 5% 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.

Significant numbers of P. squatarola 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).

In the Americas threats are not well understood, but Smith et al. (2023) likewise cite urban and wetland development as well as disturbance as likely key threats. The extent to which hunting is a threat in the Americas is largely unknown. There is subsistence level harvest of the species in Alaska; totalled numbers for this species combined with golden plovers is low (Naves et al. 2019) and there is no possibility this represents a significant threat to the species. Less clear, however, is the impact of more widespread hunting; e.g. Andres et al. (2022) found the species in 44.4% of markets in Guyana, and AFSI (2020) reported low levels of hunting in northern South America and the Caribbean.

Hunting is a probable threat to this species in parts of its range, as the hunting of shorebirds across the East Asian-Australasian Flyway is not uncommon (see, e.g., Gallo-Cajiao et al. 2020, Yong et al. 2022). The extent of hunting in the Arabian Peninsula region is poorly known, but shorebirds are occasionally targeted (Brochet et al. 2016). The extent of hunting in the Americas flyway (chiefly in Latin and South America) is not well quantified, but there is evidence that birds are harvested in Guyana (Andres et al. 2022) and probably elsewhere in the Caribbean. There is subsistence level harvest of the species in Alaska; totalled numbers for this species combined with golden plovers is low (Naves et al. 2019) and there is no possibility this represents a significant threat to the species.

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, although it is also listed on Annex II/B of the Directive as a species that may be hunted in several EU Member States. It is also listed on Annex III (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, 370 Natura 2000 sites have been designated for the conservation of this species on passage and in winter (EEA 2024). Some habitats along flyway routes are protected. The Australasian Wader Studies Group, along with BirdLife Australia's Shorebirds 2020 Project and committed volunteers continue to monitor migratory shorebirds within the East Asian-Australasian Flyway (Vine and Maurer 2016). 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 P. squatarola) 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 P. squatarola 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 organisations, communities, regional organisations like the East Asian-Australasian Flyway Partnership.

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). There is an urgent need to understand the threat posed by hunting across its range, particularly in the Americas, Africa and the Middle East, where there is a lack of even descriptive understanding on the extent to which this occurs.