Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The overall population trend is not known but it is not believed to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The global population is estimated to number c.4,800,000-8,900,000 individuals (Wetlands International 2015). The European population is estimated at 1,340,000-1,990,000 pairs, which equates to 2,670,000-3,980,000 mature individuals or 4,000,000-5,970,000 individuals (BirdLife International 2015). Combining the new figures for the European population (BirdLife International 2015) with estimates from the other populations in Wetlands International (2015) provides an overall estimate of 4,400,000-8,200,000 individuals. National population estimates include: > c.1,000 individuals on migration and > c.1,000 wintering individuals in China; c.1,000-10,000 individuals on migration and > c.1,000 wintering individuals in Taiwan, China; > c.1,000 individuals on migration and > c.1,000 wintering individuals in Korea; < c.10,000 individuals on migration and c.1,000-10,000 wintering individuals in Japan and c.10,000-1 million breeding pairs and > c.1,000 individuals on migration in Russia (Brazil 2009).
The overall population trend is unclear. Some populations have unknown trends (Wetlands International 2015). This species has undergone a large and statistically significant increase over the last 40 years in North America (361% increase over 40 years, equating to a 46.6% increase per decade; data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007). Note, however, that these surveys cover less than 50% of the species's range in North America. Between 1990 and 2013 the European population is estimated to have declined moderately (EBCC 2015).
This species breeds in north-east North America and across much of Europe and Asia, excluding the north of each continent (northern Scandinavia and north Russia), and south Asia. Some populations in North America and the milder areas of Europe are resident, with the remaining populations wintering to the south over a large range, encompassing much of the southern coast of Asia and Europe, and the central and northern coast of Africa (del Hoyo et al. 1996).
Behaviour Northern breeding populations of this species are strongly migratory although populations at lower latitudes tend to be sedentary or locally dispersive (del Hoyo et al. 1996). The species breeds between April and May (del Hoyo et al. 1996) in dense colonies of up to several thousand pairs (del Hoyo et al. 1996, Snow and Perrins 1998) often with other gull or tern species (Flint et al. 1984). It generally remains gregarious throughout the year (Snow and Perrins 1998) and may roost in large flocks during the winter (Richards 1990). Habitat Breeding The species chiefly breeds inland and shows a preference for shallow, calm (Snow and Perrins 1998), temporarily flooded wetland habitats (del Hoyo et al. 1996) with lush vegetation (Flint et al. 1984, del Hoyo et al. 1996). It forms nesting colonies on the margins of lakes (Flint et al. 1984, Richards 1990, del Hoyo et al. 1996), lagoons (Flint et al. 1984, Snow and Perrins 1998), slow-flowing rivers, deltas, estuaries (Snow and Perrins 1998) and on tussocky marshes (Flint et al. 1984, Richards 1990, del Hoyo et al. 1996), but may also nest on the upper zones of saltmarshes (del Hoyo et al. 1996, Snow and Perrins 1998), coastal dunes and offshore islands in more coastal areas (del Hoyo et al. 1996). The species will also utilise artificial sites such as sewage ponds, gravel- and clay-pits, ponds, canals and floodlands (Snow and Perrins 1998) and may nest on the dry ground of heather moors, sand-dunes, beaches (del Hoyo et al. 1996, Snow and Perrins 1998) and stony islets (Snow and Perrins 1998). Non-breeding During the winter the species is most common in coastal habitats (del Hoyo et al. 1996) and tidal inshore waters, showing a preference for inlets or estuaries with sandy or muddy beaches, and generally avoiding rocky or exposed coastlines (Snow and Perrins 1998). It may also occur inland during this season, frequenting ploughed fields, moist grasslands, urban parks, sewage farms, refuse tips, reservoirs, ponds and ornamental waters (Snow and Perrins 1998), and roosts on sandy and gravel sites or on inland reservoirs (Richards 1990). Diet Its diet consists predominantly of aquatic and terrestrial insects, earthworms and marine invertebrates (e.g. molluscs, crustaceans and marine worms) (del Hoyo et al. 1996) although it may also take fish (del Hoyo et al. 1996) (usually dead or sick) (Flint et al. 1984), rodents (e.g. voles) (Flint et al. 1984) and agricultural grain (del Hoyo et al. 1996). During the non-breeding season the species may rely heavily on artificial food sources provided by man, especially in Western Europe (del Hoyo et al. 1996), and often scavenges from refuse tips during this period (Richards 1990). Breeding site The nest is a rough construction of vegetation (Richards 1990) based on a shallow scrape (Snow and Perrins 1998) and placed on a floating mat, in broken reeds, on a hummock, or sometimes on dry, grassy or sandy ground (Flint et al. 1984, del Hoyo et al. 1996). The species shows a strong preference for nesting near vegetation (although vegetation overgrowth can lead to the desertion of colony sites) (del Hoyo et al. 1996). It usually nests in dense colonies with neighbouring nests placed an average of 1 m apart (del Hoyo et al. 1996).
The species is susceptible to avian influenza (Melville and Shortridge 2006) and avian botulism so may be threatened by future outbreaks of these diseases (Hubalek et al. 2005). It may also be threatened by future coastal oil spills (Gorski et al. 1977) and has suffered local population declines in the past as a result of egg collecting (del Hoyo et al. 1996). In some areas of its breeding range the species may also suffer from reduced reproductive successes due to contamination with chemical pollutants (del Hoyo et al. 1996). None of these, however, are thought to be significant threats to the population.
Conservation Actions Underway
The following information refers to the species's European range only: The species is listed under the African Eurasian Waterbird Agreement. Within the EU it is listed on Annex II of the Birds Directive. Within Europe it is listed in 43 marine Important Bird Areas. In the EU it is listed in 928 Special Protection Areas. Management plans established for protected sites, including monitoring and enforcement from disturbance and removal of eggs.
Text account compilers
Butchart, S., Bennett, S., Calvert, R., Ashpole, J, Ekstrom, J., Malpas, L.
BirdLife International (2019) Species factsheet: Larus ridibundus. Downloaded from http://www.birdlife.org on 21/06/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 21/06/2019.