Data Zone
Justification of Red List category
A moderately rapid reduction in the population of Greater Yellowlegs is estimated to be taking place based on analysis of migration count data, but with considerable uncertainty due to contradictory trends between Breeding Bird Survey (BBS), Christmas Bird Count (CBC) data and the migratory count data. Potentially significant levels of mortality in parts of the non-breeding range and along migratory routes have the potential to be driving declines that the poor coverage of the BBS survey for the species has so far not detected. Loss of key habitat may also contribute, though the species is able to use a wide range of wet habitat and it is unclear that the amount of habitat available has declined. The magnitude of the population decline is uncertain, and the migration count data itself may not adequately sample this species, but it is considered the most representative dataset for the species. The range and population size are large. On a precautionary basis due to the recorded rate of population reduction, Greater Yellowlegs is assessed as Near Threatened.
Population justification
The global population is currently estimated at 137,000 mature individuals (Andres et al. 2012). A modelling approach suggested 6.86 million mature individuals in Canada alone (BAM 2020). However, COSEWIC (2020) considered this approach when applied to Lesser Yellowlegs to likely overestimate true density because of birds approaching observers during point counts. The species is not covered by the Program for Regional and International Shorebird Monitoring (PRISM) surveys (Bart and Smith 2012) as it breeds further south, but the observation that these systematic surveys typically increased estimates significantly suggests the population size given by Andres et al. (2012) may be a considerable underestimate.
Trend justification
Trends from the sources available are contradictory, making the true trajectory of the population uncertain. North American Breeding Bird Survey data indicate a recent three-generation increase of 13%, but with wide credible intervals (-36 to +81% for 2.5% and 97.5% CI) (Ziolkowski Jr. et al. 2022): none of the Bird Conservation Region trends are rated as having good credibility and the survey coverage for the species is poor (ECCC 2019). But this positive trend is consistent through the whole span of the BBS data back to 1966 and certainly since 1990 when confidence intervals have been narrower. In contrast, recent migratory count data estimates a rapid reduction over three generations of 43% (95% CI -15 to -63%) (Smith et al. 2023), when earlier migration data indicated a positive annual trend between 1970 and 2016 (ECCC 2019, Ziolkowski Jr. et al. 2022). It has previously been noted that many individuals may not be detected at count sites as they prefer smaller wetland areas potentially reducing the accuracy of this survey for the species (ECCC 2019). But the abrupt change in trajectory after around 2004 is evident in this earlier data (but not noticeable at the time in context) and the recent analysis demonstrates this downturn has become a sustained decline in the numbers being recorded at the migration sites network (Smith et al. 2023).
North American Christmas Bird Count (CBC) data cover only a small proportion of the non-breeding population, with most far to the south. But this data also shows an increasing trend, but again with high uncertainty with a three-generation rate of 8% but within a range of -23 to +86% (Meehan et al. 2022). It is possible that increases in non-breeding counts in the northern part of the range may relate to ‘short-stopping’, where fewer individuals complete the expected full distance of their migration and instead stay in sites closer to breeding areas. In this context, another very rapid decline recorded from counts at non-breeding sites in Central America between 2012-2020 (van Dort et al. 2023) may help to explain some of the conflict in the data.
Overall, and taking a precautionary approach noting that each dataset has weaknesses for this species, a moderately rapid rate of reduction of 0-29% is suspected for the past three generations. The rate is not projected forwards due to the level of uncertainty.
This migratory shorebird breeds from the Alaska Peninsula, United States of America (USA) south of the north slope and east through central Canada all the way to Nova Scotia and through north central Canada from the coastal Northwest Territories, Yukon, northern British Colombia east to Hudson Bay and James Bay (Elphick and Tibbitts 2020, Fink et al. 2023). All individuals migrate from breeding areas, but a number remain in non-breeding areas each breeding season (Elphick and Tibbitts 2020, Navedo and Ruiz 2020, Fink et al. 2023). Large numbers winter in the United States in the non-breeding season, but as many migrate to the south-eastern South American grasslands (Argentina and Uruguay) and both South American coasts, scattered through high elevation wetlands in the Andes, in the Llanos of Colombia and Venezuela as well as the northern coast of South America (Elphick and Tibbetts 2020, Fink et al. 2023).
Breeds in wetland habitats from the boreal forest transition in the taiga zone to the subarctic tundra (Elphick and Tibbitts 2020). On migration and in the non-breeding season occurs in a variety of wetland habitats, fresh, brackish and saltwater, including human-made habitats such as salt evaporation ponds, flooded agriculture, ponds and reservoirs (Elphick and Tibbitts 2020). Feeds on aquatic and terrestrial invertebrates, and occasionally fish and frogs.
The species is harvested at a moderately high rate in the Caribbean Islands and a medium rate in northern South America (AFSI 2020, Andres et al. 2022). Numbers recorded as taken do not approach a Potential Biological Removal value of of 10,210 ± 2,234 (Watts et al. 2015), but a revised framework for Lesser Yellowlegs indicated a far lower threshold for sustainable take (Rivera-Milán et al. 2023, which if found to apply similarly to Greater Yellowlegs suggests harvest may be unsustainable.
The species uses a wide range of wetland habitats, but the loss of wetlands in parts of the non-breeding range and in migratory stopover sites may have reduced the area of suitable habitat in some key areas. As examples, wetlands in the south-east South American grasslands have been lost and degraded due to conversion to agriculture, principally annual crops such as soy beans (Miñarro and Bilenca 2008), and approximately 40% of wetland habitat in south east Córdoba province, Argentina, was lost in 20 years to 2007 (Brandolin et al. 2013), with intensification of use driving conversion of pasture to cropland in the Pampas (Piquer-Rodriguez et al. 2018).
Habitat shifts due to climate change on the breeding grounds may be affecting the species. How the boreal forest zone will change and then what impacts will manifest for this species remains highly uncertain but is predicted to be negative (Soja et al. 2006, Bouderbala et al. 2023).
Conservation Actions In Place
Protected in U.S. and Canada under the 1927 Migratory Bird Treaty Act. Hunting is illegal in many countries within the species range, though there is allowance for subsistence hunting in Brazil and for indigenous people in Canada and the USA (AFSI 2020). In Trinidad and Tobago a ban on all waterbird hunting was enacted in 2019 (AFSI 2020).
The Atlantic Flyway Shorebird Initiative (AFSI) has identified and undertaken a series of measures to address unsustainable harvest in the Caribbean and northern South America (AFSI 2016, 2017, 2020). An initial Potential Biological Removal estimate was generated (Watts et al. 2015). Migratory stopover habitat is largely identified and protected under the Western Hemisphere Shorebird Reserve Network (WHSRN), although this offers no legal protection.
Greater Yellowlegs is monitored via the North American Breeding Bird Survey (BBS) (Ziolkowski Jr. et al. 2022) although this covers only a small proportion of the breeding range; by the Christmas Bird Count (Meehan et al. 2022) which covers part of the non-breeding range; by the International Shorebird Survey during migration (Brown et al. 2001, Smith et al. 2023); and is partly covered by the International Waterbird Census during the non-breeding season (Wetlands International 2023).
Conservation Actions Needed
The biological and social aspects of harvest across the countries for which there is significant harvest in the species need to be fully assessed (AFSI 2016). In particular further research into harvest levels is needed in Suriname, Brazil, French Guiana, Guadeloupe and Saint-Martin and Saint Pierre and Miquelon (AFSI 2020).
Consult with the Barbados Wildfowlers Association on further lowering bag limits for the species, and delaying the start of the season to reduce the take of adult birds (Wege et al. 2014). Seek to devise, with national governments, a harvest management strategy for shorebirds in Guyana and Suriname (AFSI 2016, 2020).
Text account compilers
Martin, R.
Contributors
Nunes, A.P., Smith, P. A., Van Dort, J. & Warnock, N.
Recommended citation
BirdLife International (2024) Species factsheet: Greater Yellowlegs Tringa melanoleuca. Downloaded from
https://datazone.birdlife.org/species/factsheet/greater-yellowlegs-tringa-melanoleuca 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.