Larus thayeri 


Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Aves Charadriiformes Laridae

Scientific Name: Larus thayeri
Species Authority: Brooks, 1915
Common Name(s):
English Thayer's Gull
Taxonomic Source(s): del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A. and Fishpool, L.D.C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Lynx Edicions BirdLife International.
Taxonomic Notes: Larus glaucoides (Sibley and Monroe 1990, 1993) has been split into L. glaucoides and L. thayeri following AOU (1998).

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2015
Date Assessed: 2012-05-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S. & Symes, A.
Facilitator/Compiler(s): Butchart, S., Calvert, R., Ekstrom, J. & Malpas, L.
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 may be moderately small to large, but it is not believed to 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.
Previously published Red List assessments:
2009 Least Concern (LC)
2008 Least Concern (LC)
2004 Least Concern (LC)
2000 Lower Risk/least concern (LR/lc)
1994 Not Recognized (NR)
1988 Not Recognized (NR)

Geographic Range [top]

Range Description: Thayer's Gull is native to North America, breeding on Arctic islands Canada and wintering on the Pacific coast from south-east Alaska (USA) to north Baja California (Mexico) (del Hoyo et al. 1996).
Countries occurrence:
Canada; Greenland; Mexico; United States
Continuing decline in area of occupancy (AOO): Unknown
Extreme fluctuations in area of occupancy (AOO): No
Estimated extent of occurrence (EOO) - km2: 507000
Continuing decline in extent of occurrence (EOO): Unknown
Extreme fluctuations in extent of occurrence (EOO): No
Continuing decline in number of locations: Unknown
Extreme fluctuations in the number of locations: No
Range Map: Click here to open the map viewer and explore range.

Population [top]

Current Population Trend: Increasing
Additional data:
Continuing decline of mature individuals: Unknown
Extreme fluctuations: No Population severely fragmented: No
Continuing decline in subpopulations: Unknown
Extreme fluctuations in subpopulations: No All individuals in one subpopulation: No

Habitat and Ecology [top]

Habitat and Ecology: Behaviour This species a long-distance migrant (Olsen and Larsson 2004) that migrates south and west after breeding (del Hoyo et al. 1996, Olsen and Larsson 2004). It arrives on its wintering grounds between late-October and December and remains there until April (Alderfer 2006). The timing of breeding is inadequately known but laying has been recorded in early-June, with the species nesting in small colonies (del Hoyo et al. 1996) of 20 to 200 pairs (Gaston 1991) often near nesting Larus hyperboreus (del Hoyo et al. 1996). It is gregarious throughout the year (del Hoyo et al. 1996, Olsen and Larsson 2004) and may occur in large flocks at favoured sites (Sibley 2003) during the winter (Olsen and Larsson 2004), although it usually occurs in small numbers amongst larger flocks of other gull species (Sibley 2003). It may also forage behind fishing boats with other species of gull (del Hoyo et al. 1996). Habitat Breeding For breeding the species requires steep (Gaston 1991), coastal cliffs (del Hoyo et al. 1996, Olsen and Larsson 2004) up to three km inland (Gaston 1991) along Arctic shores and rocky islands (Godfrey 1979, del Hoyo et al. 1996). Non-breeding During the winter the species frequents a variety of habitats surrounding coastal shores and estuaries (Alderfer 2006), often foraging around fishing harbours, refuse dumps and settlements (del Hoyo et al. 1996, Olsen and Larsson 2004). It may also occur on inland freshwater lakes (Godfrey 1979, Olsen and Larsson 2004), rivers (Godfrey 1979), flooded land and occasionally agricultural fields (Olsen and Larsson 2004) especially when on migration (Godfrey 1979). Diet Breeding Non-breeders are known to take refuse and offal from around settlements during the breeding season, but the diet of nesting pairs and nestlings is largely unknown (del Hoyo et al. 1996). Non-breeding During the winter the species takes fish, marine invertebrates and offal (del Hoyo et al. 1996). Breeding site The nest is a cup (del Hoyo et al. 1996) of grass or other available vegetation placed on a rocky cliff ledge (Godfrey 1979) usually on the coast (Godfrey 1979, del Hoyo et al. 1996, Olsen and Larsson 2004) or surrounding a near-coastal freshwater site (Godfrey 1979). The species shows a preference for large cliff ledges 920 cm2 in area (on average), and often nests on cliffs below colonies of Larus hyperboreus (del Hoyo et al. 1996).
Systems: Terrestrial; Marine
Continuing decline in area, extent and/or quality of habitat: Unknown
Generation Length (years): 11.5
Movement patterns: Full Migrant
Congregatory: Congregatory (and dispersive)

Citation: BirdLife International. 2015. Larus thayeri. The IUCN Red List of Threatened Species 2015: e.T22728995A85052004. . Downloaded on 30 November 2015.
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