Justification of Red List Category
This species is classified as Least Concern. It 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 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). Despite the fact that the population trend appears to be decreasing, the decline is currently thought to be part of a longer-term fluctuation following previous increases. Should new evidence suggest that it is continuing to decline the species would warrant uplisting to Near Threatened.
The population is estimated to number 1,370,000-1,620,000 mature individuals which equates to 2,060,000-2,430,000 individuals (BirdLife International 2015).
L. a. argentatus was listed as stable from 1990-2000, while L. a. argenteus declined during the same period (Wetlands International 2014). Recently published data estimates the population to be decreasing at a rate approaching 30% in 39 years (three generations) (BirdLife International 2015). However it is thought that these recent declines are most likely to form part of a longer-term fluctuation following previous increases. Recent declines may in part be due to better waste management (N. Baccetti, T. Lehtiniemi, H. Meltofte, L. Raudonikis, K. Steiof and R. Virkkala in litt. 2015). The population should be closely monitored to establish whether it shows any sign of stabilising.
The species inhabits coastal and near-coastal areas but may also forage inland on large lakes and reservoirs, fields and refuse dumps (del Hoyo et al. 1996). It has no specific breeding habitat (del Hoyo et al. 1996) but may show a preference for rocky shores with cliffs, outlying stacks or islets (del Hoyo et al. 1996, Snow and Perrins 1998), otherwise nesting on rocky and grassy islands, sandy beaches (del Hoyo et al.1996), dunes (Richards 1990), gravel bars, saltmarshes, rocky outcrops, buildings, claypits (del Hoyo et al. 1996), tundra with reeds or hummocks (Flint et al. 1984), swampy lowlands near lakes and on river islands (Flint et al.1984). When inland on migration the species also shows a preference for large river valleys (Flint et al. 1984). Although Herring Gulls exploit refuse tips and farmland extensively all year round, their breeding distribution is extremely coastal compared to other Larus gulls (other than L. marinus) (Gibbons et al. 1993).
The species has a highly opportunistic diet and will exploit almost any superabundant source of food (del Hoyo et al.1996). It takes fish, earthworms, crabs and other marine invertebrates (e.g. molluscs, starfish or marine worms), adult birds, bird eggs and young, rodents, insects (e.g. ants), berries and tubers (e.g. turnips) (del Hoyo et al. 1996). It also scavenges at refuse dumps, fishing wharves and sewage outfall zones and frequently follows fishing boats (del Hoyo et al. 1996, Huppop and Wurm 2000). The feeding range has been variously reported as 35 km (for breeding herring gulls in a Dutch colony) (Spaans 1971), 41 km (in Westphalia, Germany, outside the breeding season) (Sell and Vogt 1986), 50 km (for breeding birds in Morocco) (Witt et al. 1981) and 70 to 100 km (for herring gulls breeding in Denmark) (Klein 1994). Several other studies have reported shorter foraging distances (Verbeek 1977, Witt et al. 1981, Sibley and McCleery 1983, Cramp and Simmons 1983, Nogales et al. 1995, Pons and Migot 1995, BirdLife International 2000). Refuse tips are frequently exploited by foraging individuals (Sibley and McCleery 1983, Nogales et al. 1995, Pons and Migot 1995) and so the feeding distribution of some colonies will be determined by location of refuse dumps (BirdLife International 2000). On the basis of a simple density model of birds at sea, it has been estimated that 95% of herring gulls breeding on Terschelling in the Dutch Wadden Sea foraged within 54 km of the colony (BirdLife International 2000).
Northern breeding populations of this species are migratory (del Hoyo et al. 1996) although populations in the south are nomadic or completely non-migratory (Flint et al. 1984). Outside of the breeding season the species is highly gregarious and gathers in large flocks in favoured sites (Richards 1990, Snow and Perrins 1998). Individuals show foraging site fidelity (Shamoun-Baranes and van Loon 2006).
The species is at risk from reductions in food supplies due to changes in fishing practices. Reduction in discards has greatly reduced available food in parts of the species range that had seen rapid increases in the previous century. Further, trophic shifts have impacted fishing activity and catch size, which appears to be directly related to colony reproductive success: lower catches are resulting in lower breeding success and the decline of colonies in the UK (Foster et al. 2017). The species is also vulnerable to collisions with wind turbines (Bradbury et al. 2014) was the most frequently recorded casualty in a study of 4.7 km of the English coastline over 11 years (Newton and Little 2009). In the past, persecution has represented a significant source of mortality however, the EU directive (2009/147/EC) has made it an offence to kill birds or destroy eggs without license. This has likely resulted in a reduction in mortality due to persecution, however, there is still some level of culling, with 5,000 birds culled under license 2010-12 in the UK (Coulson 2015). The threat is unlikely to disappear, with recent paper calling for lethal controls for closely related Larus spp. in Gulf of Maine (Scopel and Diamond 2017) however, this is thought to cause negligible declines. Botulism reports have been increasing in Britain in last 45 years and, despite the number of deaths not having been quantified, it is suggested to have been a factor in the population declines in Britain (Coulson 2015).
Conservation Actions Underway
The species is covered by the African Eurasian Waterbird Agreement. In the EU it is listed under Annex II of the Birds Directive.
Conservation Actions Proposed
On-board monitoring programmes for seabird bycatch in fishing vessels, and implementation of mitigation measures where appropriate. Increased understanding of movements to assist placement of offshore wind farms.
Text account compilers
Symes, A., Taylor, J., Butchart, S., Ekstrom, J., Ashpole, J, Calvert, R., Hatchett, J., Hibble, R., Malpas, L., Stuart, A.
Yésou, P., Steiof, K., Bourne, W.R.P., Morkunas, J., Mischenko, A.L., Lehtiniemi, T., Virkkala, R., Baccetti, N., Petkov, N., Raudonikis, L.
BirdLife International (2019) Species factsheet: Larus argentatus. Downloaded from http://www.birdlife.org on 18/09/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 18/09/2019.