Calidris falcinellus (del Hoyo and Collar 2014) was previously placed in the genus Limicola.

Calidris falcinellus is listed as Vulnerable because of estimated declines likely exceeding 30% in the past three generations (13 years). The causes of these declines are not well unknown, but the drainage of peatlands for forestry in its European breeding grounds has been suggested as a very likely contributor to declines. Across its passage and wintering grounds it is also exposed to numerous other threats, including habitat loss due to land reclamation, hunting and disturbance from fishing activities.

Two subspecies: nominate C. f. falcinellus breeds in Scandinavia and north-west Russia, while C. f. sibirica breeds in north-east Siberia. The former winters widely across east Africa and Arabia to western India and Sri Lanka, while the latter winters in east India, throughout South-East Asia, the Philippines, Indonesia and Australia.

Divided into two subspecies, with the nominate breeding in Fennoscandia and north-west Russia, and sibirica breeding in central and eastern Siberia. Almost all of the nominate subspecies breeds in Europe, where there are estimated to be be 30,000-44,000 pairs, most of which (25,000-35,000 pairs) are in Finland (Keller et al. 2020). A much smaller number (<1,200 pairs) breed in European Russia (Keller et al. 2020). When immatures and non-breeding birds are taken into account, these numbers are similar to the wintering population of 61,000-110,000 birds estimated (BirdLife International 2021, Wetlands International 2023). Taxon sibirica is estimated to number 30,000 birds in the East Asian-Australasian Flyway (Mundkur and Langendoen 2022, Hansen et al. 2023); assuming approximately 0.6-0.8 birds are mature, this equates to c.18,000-24,000 breeding pairs. Overall, the global population of this species is estimated a 48,000-68,000 breeding pairs, or 96,000-136,000 mature individuals.

Behaviour This species is a full migrant, and migrates on a broad front (del Hoyo et al. 1996) by making short flights between a series of stop-over sites (Verkuil et al. 2006). Adults breeding in Fennoscandia leave the breeding grounds in July (juveniles departing in August), and stop-over in substantial numbers in Sivash, southern Ukraine, on the Middle Eastern coasts, Caspian Sea and Bulgarian seaboard, before arriving in wintering grounds in Africa, Pakistan and south India between August and early-October (del Hoyo et al. 1996). Eastern breeding populations migrate on a broad front across the taiga, or along the eastern edge of the continent between September and October, and return in April-May (del Hoyo et al. 1996). The Fennoscandian breeding population departs the wintering grounds in the spring between mid-April and early-June (del Hoyo et al. 1996). A few non-breeding birds also remain at the wintering sites during the summer (del Hoyo et al. 1996). Breeding occurs in early- to late-June in Fennoscandia, and between mid-June and early-July in Russia, pairs nesting in loose colonies of 2-10 nests, usually spaced 80-100 m apart (del Hoyo et al. 1996). The species migrates singly or in small groups, although during the spring migration flocks of up to several hundred can occur (del Hoyo et al. 1996). Habitat Breeding This species breeds in the wettest parts of bogs (Snow and Perrins 1998) and on open peatland; the Scandinavian and north-west Russian populations breeding in the subarctic montane and lowland zones above 200 m (del Hoyo et al. 1996) (around 1,000 m in Norway) (Snow and Perrins 1998), and the Siberian population breeding in wet Arctic tundra (del Hoyo et al. 1996). Non-breeding On migration this species shows a preference for muddy and boggy areas on the shores of ponds and lakes, but it is also found on shallow freshwater, brackish and saline (sometimes hyper-saline) lagoons, temporary swamps, flooded rice-fields, overgrazed wet meadows, inlets of fjords (del Hoyo et al. 1996, Snow and Perrins 1998). The species mainly overwinters on large, soft intertidal mudflats, in brackish lagoons, on saltpans (del Hoyo et al. 1996), sewage farms and saltmarshes (Snow and Perrins 1998). Diet This species is omnivorous, its diet consisting of marine nereid worms, small bivalves and snails, crustaceans (e.g. amphipods), adult and larval insects (e.g. beetles, flies, grasshoppers, ants) (del Hoyo et al. 1996), as well as the seeds of aquatic plants (Snow and Perrins 1998). Breeding site The nest is a cup on top of a wet sedge or moss cushion, well raised above the water level (Johnsgard 1981).

Numerous threats identified across its range, although the extent to which these are contributing to estimated population declines is largely unknown. In Finland, which likely hosts at least 50% of the global breeding population, drainage of peatlands for forestry is considered the chief threat (Fraixedas et al. 2017, Keller et al. 2020, BirdLife International 2021) and this was also attributed previously to local extinctions in Norway (van Gils and Wiersma 1996). 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 8% of the Asian-East African Flyway has been reported to overwinter (Eriksen 1996), 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). Significant numbers of C. falcinellus migrate down the Yellow and East China Seas where habitat loss and hunting are plausibly significant threats. Astonishingly, the extent of reclaimed land along the Yellow Sea coastline now exceeds the extent of remaining intertidal mudflat (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 Australia, there are unlikely to be any substantial threats.

Hunting has not been identified as a specific threat to this species, but hunting of shorebirds across the East Asian-Australasian Flyway is not uncommon (see, e.g., Gallo-Cajiao et al. 2020, Yong et al. 2022) and it is possible this species is exploited. However, it is unknown whether this is driving population declines.

Conservation Actions Underway
There is regular/annual monitoring of this species across its breeding, passage and wintering ranges. This species is not listed on the annexes of the European Union (EU) Birds Directive, but is covered by the general protection regime provided by Article 1 of the 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 I of the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA). Across the EU, 156 Natura 2000 sites have been designated for this species, especially in Finland (which holds most of the EU breeding population) but also in countries where it occurs on passage (EUNIS 2024). It 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, although to date (June 2024) the LIFE project database does not list any projects that have taken practical conservation measures for this species. Outside of the EU it occurs in numerous protected areas, particularly on passage and wintering grounds. 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. falcinellus) 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. North Korea (which is only of marginal importance to this species) became a Party to the Ramsar Convention and joined the EAAF Partnership in 2018, demonstrating their commitment to the conservation of coastal wetlands. 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 Southeast Asian countries:  Mongolia, China, Bangladesh, Viet Nam, Cambodia, Lao PDR, Philippines, Thailand, Malaysia and Indonesia, all of which are used by C. falcinellus on northbound and southbound migrations between breeding and wintering areas. 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. The discharge of toxic pollutants into coastal wetlands may also be a threat.

Conservation Actions Proposed
In Europe (particularly Finland), there is an urgent need to safeguard peatland breeding grounds from forestry.  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. In order to evaluate the success of the conservation actions listed above, robust monitoring is needed, preferably at all stages of its migration cycle. 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).