Data Zone
Justification of Red List category
This species has a large geographic range size (extent of occurrence >16 million km2 in both the breeding and non-breeding seasons), and so does not approach Criterion B thresholds. It also has a large estimated population size (250,000 mature individuals; Partners in Flight 2023), and so does not approach Criteria C or D thresholds. Considering its population trend over three generations (c. 18 years), the data presented in Smith et al. (2023) indicate a slow decline of c. 10%, albeit with large confidence intervals. This is broadly consistent with evidence of similar rates of decline from the Breeding Bird Survey (c. 7%; Ziolkowski et al. 2022), eBird (c. 6%; Fink et al. 2023) and Partners in Flight (2023; c. 15%). In recent years, a steeper decline has been recorded on the Pacific coast by the Migratory Shorebird Project (unpublished data), although this covers a relatively small proportion of the population. Conversely, data from the Christmas Bird Count (Meehan et al. 2022) indicate a stable population. Although the population is declining, it does not currently appear to be declining at a rate approaching Criterion A thresholds. Hence, the species continues to warrant listing as Least Concern.
Population justification
It has a large estimated population size of 250,000 mature individuals (Partners in Flight 2023).
Trend justification
Considering its population trend over three generations (c. 18 years), the data presented in Smith et al. (2023) indicate a slow decline of c. 10%, albeit with large confidence intervals. This is broadly consistent with evidence of similar rates of decline from the Breeding Bird Survey (c. 7%; Ziolkowski Jr et al. 2022), eBird (c. 6%; Fink et al. 2023) and Partners in Flight (2023; c. 15%). In recent years, a steeper decline has been recorded on the Pacific coast by the Migratory Shorebird Project (unpublished data), although this covers a relatively small proportion of the population. Conversely, data from the Christmas Bird Count (Meehan et al. 2022) indicate a stable population. Overall the global population is estimated to have declined by 6-15% over the past three generations.
The species comprises two distinct subspecies, differentiated by their breeding habitats in North America. Eastern Willets (T. s. semipalmata) breed in estuarine marshes along the Atlantic and Gulf Coasts, while Western Willets (T. s. inornate) breed in wet grasslands and prairies in the interior west of North America (Heath et al. 2021). T. s. inornate primarily use non-breeding habitats along the Pacific Coast of the United States, though their non-breeding range also extends to the US Atlantic and Gulf Coasts and the Pacific Coast of Central and South America. In contrast, T. s. semipalmata winter in Central and South America, encompassing much of their known non-breeding range (Huysman et al. 2020).
The two subspecies are threatened to varying degrees by hunting. While Western Willets (Tringa semipalmata inornate) are generally protected from hunting threats by the passage of the Migratory Bird Treaty Act in 1918, Eastern Willets (T. s. semipalmata) face ongoing hunting pressures on their non-breeding grounds in Guyana, Suriname, French Guiana, Brazil and the Caribbean (Watts and Turrin 2016, Atlantic Flyway Shorebird Initiative Harvest Working Group 2020, AFSI 2020, Andres et al. 2022). Suriname, in particular, has the highest harvest of migratory shorebirds in the Western Hemisphere (Atlantic Flyway Shorebird Initiative Harvest Working Group 2020). The extent of hunting pressure across different non-breeding locations remains poorly understood, but research by Watts et al. (2015) indicates that both subspecies, especially T. s. semipalmata, have low sustainable harvest rates compared to other shorebirds, making them particularly vulnerable to hunting. T. s. semipalmata breeding on the Atlantic Coast face greater risks during migration compared to Gulf Coast breeders, as they cross the Caribbean and winter in northern South America, where they encounter high harvest levels (Watts and Turrin 2016).
Habitat development, notably in the San Francisco Bay area, poses another significant threat to the species (Warnock et al. 2021). Throughout their non-breeding range, the species is confronted with the loss of tidal mudflats and mangroves, critical habitats that have dwindled in extent in a few key countries in recent years (Thomas et al. 2017, Murray et al. 2019). In Mexico, economic development threatens important shorebird sites through agriculture, commercial fishing, shrimp aquaculture, tourism, and hunting. Interior-staging Willets, which depend on shallow-water habitats, are also affected as many of these habitats are converted to agriculture or managed at high water levels for irrigation and tourism.
Grasslands, which are critical habitats for the species, are the most threatened ecosystem worldwide, with less than 1% remaining intact in some parts of North America. While grazing can help maintain low vegetation, overgrazing is a significant issue. The conversion of native grasslands to agriculture creates 'sink' habitats where nesting attempts often fail, and Willets tend to avoid the tall, dense covers planted for waterfowl (Lowther et al. 2020). The draining and ploughing of wetlands for crops, along with maintaining high water levels for tourism and irrigation, further degrade these habitats.
Text account compilers
Ekstrom, J., Chad, E., Butchart, S.
Recommended citation
BirdLife International (2024) Species factsheet: Willet Tringa semipalmata. Downloaded from
https://datazone.birdlife.org/species/factsheet/willet-tringa-semipalmata on 23/11/2024.
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 23/11/2024.