Data Zone
Justification of Red List category
This species has a large geographic range size (extent of occurrence >8 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 (460,000 mature individuals; Partners in Flight 2023), and so does not approach Criteria C or D thresholds. Considering its population trend over three generations (c. 14 years), the data presented in Smith et al. (2023) indicate a slow decline of c. 16% (with a wide confidence interval), although the underlying interannual trend data suggest a fluctuating population. There is some evidence of recent declines from the western USA and Mexico (Migratory Shorebird Project, unpublished data) and from eBird (Fink et al. 2023), but also consistent evidence of a modest overall recent increase in North America from both the Christmas Bird Count (Meehan et al. 2022) and the Breeding Bird Survey (Ziolkowski et al. 2022). The population trend is therefore considered unknown, but there is little evidence the species is declining at a rate that approaches Criterion A thresholds. The species is therefore listed as Least Concern.
Population justification
The global population is estimated to number 460,000 mature individuals (Partners in Flight 2023).
Trend justification
Considering its population trend over three generations (c. 14 years), the data presented in Smith et al. (2023) indicate a slow decline of c. 16% (with a wide confidence interval), although the underlying interannual trend data suggest a fluctuating population. There is some evidence of recent declines from the western USA and Mexico (Migratory Shorebird Project, unpublished data) and from eBird (Fink et al. 2023), but also consistent evidence of a modest overall recent increase in North America from both the Christmas Bird Count (Meehan et al. 2022) and the Breeding Bird Survey (Ziolkowski et al. 2022). Because of the inconsistencies in the data available, the trend is considered unknown.
The species inhabit western North America from March to October and migrate to wintering grounds in coastal California, southern Texas, Florida, Louisiana, and south to Guatemala.
During the breeding season, American Avocets inhabit a variety of habitats including salt ponds, potholes, shallow alkaline wetlands, mudflats of inland lakes, impoundments, and evaporation ponds. These wetlands are typically characterised by common cattail (Typha latifolia), bulrushes (Schoenoplectus spp.), or sedges (Carex spp.). However, they spend most of their time in open areas devoid of vegetation, or areas dominated by glasswort (Salicornia spp.), salt grass (Distichlis spp.), and greasewood (Sarcobatus spp.) in upland regions (Ackerman et al. 2020).
Numerous threats have been identified for this species although the current uncertainty over the population trend hampers conclusions over the impact these are having. Threats identified include wetland loss and conversion, driven chiefly by agricultural and urban projects (Ackerman et al. 2020). Although surrogate habitats like salt evaporation ponds and agricultural fields have partially offset these losses, they are not without challenges. For instance, plans to convert former salt ponds in San Francisco Bay back into tidal marsh habitat threaten the species' established breeding population there, as tidal marshes are not preferred foraging or nesting habitats for these birds (Hartman et al. 2021). Furthermore, habitats in the Pacific Flyway crucial for breeding, staging, and wintering, such as those in the San Francisco Bay, are already suffering from pollution from agricultural and industrial degradation of water quality (Ackerman et al. 2014, Harvey et al. 1992) and rising salinity levels (Hannam et al. 2009).
Pesticides and other contaminants pose potential threats to R. americana across their habitats. DDT and its metabolites, such as DDE, have accumulated in some avocet populations. Selenium, while essential in low doses, becomes toxic at higher levels, often contaminating wetlands through agricultural practices. Selenium bioaccumulation has led to reproductive failures and developmental abnormalities in avocet embryos and chicks, particularly notable at sites like Kesterson National Wildlife Refuge in California. Additionally, methylmercury, which biomagnifies in aquatic food webs, poses a risk, affecting avocet reproduction and development in contaminated areas like San Francisco Bay and Great Salt Lake (Ackerman et al. 2020).
Climate change poses a possible threat to wetlands by disrupting their hydrological cycles, which are crucial for their ecological functions. Projections suggest a notable decline in the extent of inundated wetlands throughout the south-central Great Plains by the end of the century, with eastern regions expected to be particularly affected (Londe et al. 2024) . The increased frequency of extreme weather events, such as droughts and intense precipitation, further destabilises wetland ecosystems by altering their hydrological patterns. These changes undermine the critical role of wetlands as crucial stopover sites for migratory wetland birds including as R. americana, potentially limiting their access to essential resources during migration (Londe et al. 2024).
A sizable shorebird with long legs, measuring 43–47 cm in length, including a bill of 8.2- to 9.5-cm length, and a wingspan reaching up to 91 cm, weighing between 275–350 g. Both sexes exhibit similar plumage but differ in size (males larger) and bill shape (females have a shorter, more strongly recurved bill). Plumage varies seasonally: rusty head and neck in breeding plumage (Alternate), and light grey in winter plumage (Basic). Legs are greyish-blue, with toes that are more than 50% webbed, and a small hallux (Ackerman et al. 2020).
Text account compilers
Murray-Watson, R., Hermes, C., Chad, E.
Contributors
Butchart, S. & Ekstrom, J.
Recommended citation
BirdLife International (2024) Species factsheet: American Avocet Recurvirostra americana. Downloaded from
https://datazone.birdlife.org/species/factsheet/american-avocet-recurvirostra-americana 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.