Data Zone
Justification of Red List category
This large shorebird has declined rapidly according to monitoring of non-breeding sites that hold the majority of the population and from a transect survey of a significant part of the breeding range. There is considerable uncertainty in the rate of the reduction, but it is estimated to fall between 20-49% 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 Vulnerable.
Population justification
The global population is estimated to number 270,000 mature individuals (Partners in Flight 2023), and is assumed to be structured into two subpopulations that accord with the two species recognised in the species.
A combination of monitoring data from breeding, migration and especially non-breeding sites indicates that there is currently a rapid population reduction underway (Ziolkowski et al. 2022, Muñoz-Salas et al. 2023, Smith et al. 2023).
Trend justification
Data from the North American Breeding Bird Survey (BBS) indicate declines of c.17% in the three-generation period 1994-2021, with no indication the rate is slowing (Ziolkowski Jr. et al. 2022). Incorporating a combination of U.S. Geological Survey and Canadian Wildlife Service analyses of BBS survey data through 2021, an overall reduction of 31.0% (-43.8 to -16.4%) within three generations was estimated in the Avian Conservation Assessment Database December 2023 update (Partners in Flight 2023). There appear to have been an acceleration in the rates of reduction in the past few years, with the Prairie Potholes Bird Conservation region (the core part of the breeding range) showing a sustained and worsening trend, although an increase is noted for the smaller population in the Badlands/Prairies Bird Conservation Region (Ziolkowski Jr. et al. 2022, N. Warnock in litt. 2024).
Surveys of migratory stopover locations throughout North America (Smith et al. 2023) support the fact that a moderately rapid to rapid reduction is taking place, with an estimated reduction of 28.9% in three generations. However this trend has poor precision and the majority of the population is not sampled by the network of sites involved: the trend has wide confidence intervals of -75.9% to +55.0% (Smith et al. 2023).
The most concerning data come from monitoring of non-breeding areas. Wintering populations of Marbled Godwits in north-west Mexico and California are thought to have declined by 7.7% annually based on Migratory Shorebird Project data during 2011–2019 (Muñoz-Salas et al. 2023). This is equivalent to a three-generation reduction of c.89%, and it is suspected that about half of the non-breeding population is expected to occur in this area. Elsewhere however, trends appear to be stable. Christmas Bird Count data (Meehan et al. 2022) show a relatively stable/slightly increasing trend overall for the three-generation period to 2021. Also, there are well-studied sites on the west coast that have remained stable, for example Tomales Bay (Warnock et al. 2021): it is possible this represents a high-quality site that attracts individuals up to the carrying capacity of the site, hence counts would remain constant while other sites see declining numbers. An alternative possible explanation for the conflicting trends may be ‘short-stopping’, where fewer individuals complete the expected full distance of their migration and instead stay in sites closer to breeding areas, although declines noted further south are not offset by stability at some sites further north.
Overall, based on data sources that cover most of the species’ range, the population decline is estimated to fall within the band 20-49% for the past and current three generations, up to 2037 (based on trend data accelerating after 2010). Uncertainty over the future rate of decline means that a value for the future three generations is not determined.
Most breed in the northern grasslands (prairie potholes region) of the United States of America (USA) and southern Canada, with small, isolated populations along coast of James Bay and on the Alaska Peninsula. Those breeding in Alaska are recognised as a separate subspecies, L. f. beringiae (Gratto-Trevor 2020), while the James Bay population are considered to belong to the nominate subpopulation. All individuals migrate from breeding areas to winter coastally in North and Central America, with greatest concentrations in central to southern California and Mexico but birds found south to Panama (Gratto-Trevor 2020) and less regularly in Ecuador and northern Peru (Fink et al. 2023). The breeding range is more restricted than the non-breeding and is used for the extent of occurrence: this still exceeds 4 million square kilometres. However, given the estimated rates of population reduction it is inferred that the Area of Occupancy is declining, although uncertainty over the drivers of decline means that it is not possibly to infer that the area, extent or quality of habitat is declining.
Limosa fedoa primarily inhabit North American prairie wetlands during the breeding season, where they feed on invertebrates, plant material and small fish, migrating to coastal mudflats, estuaries and sandy beaches for the non-breeding season where they predominately eat worms, bivalves and crustaceans (Gratto-Trevor 2020). A proportion of the population remains in non-breeding areas each year.
Parmelee, but the primary threat identified for the species is the loss of habitat in breeding and staging sites due to conversion to agriculture, particularly to crops and indeed partly the switch to crops from pasture (Melcher et al. 2010). Infrastructure development, including that associated with the oil industry, and the subdivision of suitable habitat by roads are also considered to have reduced available habitat in breeding areas (Melcher et al. 2010). In the non-breeding areas large-scale development is also cited as a threat causing habitat loss and degradation (Gratto-Trevor 2020, Muñoz-Salas et al. 2023).
The species has suffered mortality from periodic botulism outbreaks in staging sites during the post-breeding migration, which can cause notable additional mortality but to date do not appear to have long-term impacts (Melcher et al. 2010). Collision mortality with powerlines in the breeding areas appears to be high, especially in S Alberta where density of powerlines is high: multiple deaths and injuries likely to result in death or failed reproduction have been reported (Gratto-Trevor 2020). This mortality is not suspected to have large population impacts, but may cause slow declines for the adjacent breeding population.
Historically hunted, though the species is protected by law and there is no evidence this remains a significant threat.
Possible alternative drivers for recent declines include disease, direct or indirect impacts of agricultural chemicals, impacts of increasing rates of disturbance in non-breeding areas (especially beaches) or currently unidentified impacts of a changing climate regime in either breeding, staging or non-breeding sites (Melcher et al. 2010, Gratto-Trevor 2020, Muñoz-Salas et al. 2023). Dewatering of regions has been cited as potential threat in non-breeding and migration sites but impacts are unknown (Melcher et al. 2010). Research is needed to identify which may be causing population impacts.
Conservation Actions Underway
No targeted actions known, however protected by the U.S. Migratory Bird Treaty Act.
Conservation Actions Proposed
Continue to monitor population trends. Investigate threats. Protect and manage breeding habitat, as well as major coastal staging and wintering sites.
Text account compilers
Vine, J., Martin, R.
Contributors
Warnock, N. & Smith, P. A.
Recommended citation
BirdLife International (2024) Species factsheet: Marbled Godwit Limosa fedoa. Downloaded from
https://datazone.birdlife.org/species/factsheet/marbled-godwit-limosa-fedoa on 23/12/2024.
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 23/12/2024.