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 very 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.
Delany and Scott (2006) estimate the population at 255,000-525,000 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).
This species is found in North America, breeding from western Alaska (USA) to British Columbia, and east to eastern Quebec (Canada). It winters further south to northern Mexico on the Pacific and Atlantic coast including the Carribean. It can also be found wintering inland from Lake Erie to the valley of the Mississippi (del Hoyo et al. 1996).
Bonaparte's gull breeds on ponds or muskeg in coastal and inland areas, nesting mainly in low lying spruce and ramaracks close to or over water but up to 600 m in Alaska. It feeds on small fish, krill, amphipods and insects with the proportions varying geographically and seasonally. It feeds mainly by surface-seizing and diving, usually in flocks exceeding 2,000 birds over the incoming tide. It arrives at breeding grounds in early May, laying within the month. It is a non-colonial species though nests may be clumped (del Hoyo et al. 1996).
At present there are no factors thought to pose a genuine threat to this species, although climate change could potentially affect the species in the future.
Text account compilers
Butchart, S., Ekstrom, J., Calvert, R.
BirdLife International (2019) Species factsheet: Larus philadelphia. Downloaded from http://www.birdlife.org on 22/03/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/03/2019.