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 population trend appears to be increasing, and hence the species does not 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.
Wetlands International (2018) estimate the population size at 2,550,000 individuals.
This species has undergone a small or statistically insignificant increase over the last 40 years in North America (data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007).
The Ring-billed Gull breeds in the USA and Canada from north California, east Washington and interior British Columbia, across the prairie provinces, north mountains and plain states. Also from the Great Lakes east to the coast. It winters in the southern portion of its breeding range south to the Gulf Coast, Mexico, Central America, Greater and Lesser Antilles (del Hoyo et al. 1996).
This species inhabites coasts, rivers, estuaries, reservoirs and rubbish dumps. It is a highly opportunistic feeder, owing to its varied diet including fish, insects, earthworms, refuse, offal, fiddler crabs, dates, fish eggs, grain, rodents and birds. It lays from late April to May, though this can be delayed in the north of its range due to snow cover. Colonies are often very large and found on low-lying islands in freshwater lakes, on wet meadows and rarely on rivers. Its large, bulky nests are usually built beside rocks, driftwood or vegetation (del Hoyo et al. 1996).
At present there are no factors thought to pose a genuine threat to this species.
Text account compilers
Ekstrom, J., Butchart, S., Calvert, R.
BirdLife International (2019) Species factsheet: Larus delawarensis. Downloaded from http://www.birdlife.org on 17/02/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 17/02/2019.