NT
Heermann's Gull Larus heermanni



Taxonomy

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. Volume 1: Non-passerines. Lynx Edicions BirdLife International, Barcelona, Spain and Cambridge, UK.

IUCN Red list criteria met and history
Red List criteria met
Critically Endangered Endangered Vulnerable
- - -

Red List history
Year Category Criteria
2020 Near Threatened D2
2018 Near Threatened D2
2016 Near Threatened D2
2012 Near Threatened D2
2010 Near Threatened D2
2008 Near Threatened D2
2006 Near Threatened
2004 Near Threatened
2000 Lower Risk/Near Threatened
1994 Lower Risk/Near Threatened
1988 Lower Risk/Least Concern
Species attributes

Migratory status full migrant Forest dependency Does not normally occur in forest
Land mass type Land-mass type - continent
Average mass -
Distribution

Estimate Data quality
Extent of Occurrence breeding/resident (km2) 1,100,000 medium
Extent of Occurrence non-breeding (km2) 3,560,000 medium
Extent of Occurrence breeding/resident (km2) 43 medium
Number of locations 5 -
Severely Fragmented -
Population and trend
Value Data quality Derivation Year of estimate
No. of mature individuals 350000 medium estimated 2016
Population trend Unknown poor not applicable -
Decline (3 years/1 generation past) - - -
Decline (5 years/1 generation past) - - -
Decline (10 years/1 generation past) - - -
Decline (10 years/3 generation future) - - -
Decline (10 years/3 generation past and future) - - -
Number of subpopulations - - -
Percentage in largest subpopulation - - -
Generation length (yrs) 9.65 - - -

Population justification: Larus heermanni is estimated to have a population of 350,000 mature individuals (Partners in Flight 2019), ~92% of which nest on Isla Rasa, Mexico (Burger and Gochfeld 1996). Numbers on Isla Rasa are similar to estimates in the late 1960s, but there have been significant fluctuations with a low of 55,000 pairs in 1975 (Burger and Gochfeld 1996). There are further throughout to be 150 pairs on George Island, 1,500 on Cholluda (Burger and Gochfeld 1996), 4,000 on Cardonosa and 200 breeding individuals on San Il de Fonso (Velarde 1999) however, more recent surveys are required to confirm such figures.

Trend justification: The overall population trend is fluctuating (Delany and Scott 2006). 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). These surveys however cover less than 50% of the species' range in North America. In the last eight years, almost total breeding failure has occurred in five nesting seasons. This is mainly due to environmental anomalies, that result in lack of food availability and, secondarily to overfishing of small pelagic fish (mainly Pacific sardine) their main food sources. An analysis of the trend of the population of this species is in process, to be able to predict the rate of population fluctuation over several years.


Country/territory distribution
Country/Territory Occurrence status Presence Resident Breeding Non-breeding Passage
Canada N Extant Yes
Costa Rica V Extant Yes
Guatemala V Extant
Mexico N Extant Yes
USA N Extant Yes

Important Bird and Biodiversity Areas (IBA)
Country/Territory IBA Name
Mexico Isla Ángel de la Guarda
Mexico Islas Benitos
Mexico Isla Isabel
Mexico Isla Rasa
Mexico Isla San Pedro Mártir
Mexico Islas Marietas
USA Channel Islands - Northern
USA San Diego Bay - South
USA Santa Clara River Valley
USA North San Diego Lagoons
USA Point Mugu
USA San Clemente Island
Mexico Bahía de Ceuta - Cospita
Mexico Farallon San Ignacio
USA Port Angeles Harbor/Ediz Hook
Mexico Carricitos - Cacaxtla - Río Piaxtla
Mexico Estero Cardonal
Mexico Estero Santa Cruz
Mexico Estero del Soldado
Mexico Archipiélago Salsipuedes
Mexico Isla Cedros
Mexico Isla San Ildefonso
Mexico Isla San Roque
Mexico Sistema Algodones
Mexico Sistema Guásimas
Mexico Presa Cajón de Peñas
Mexico Isla Asunción
Mexico Bahía e Islas de San Jorge
Mexico Isla Guadalupe
Mexico Bahía Santa María

Habitats & altitude
Habitat (level 1) Habitat (level 2) Importance Occurrence
Marine Coastal/Supratidal Coastal Brackish/Saline Lagoons/Marine Lakes major non-breeding
Marine Coastal/Supratidal Sea Cliffs and Rocky Offshore Islands major breeding
Marine Intertidal Rocky Shoreline major breeding
Marine Intertidal Sandy Shoreline and/or Beaches, Sand Bars, Spits, Etc suitable non-breeding
Marine Intertidal Sandy Shoreline and/or Beaches, Sand Bars, Spits, Etc suitable breeding
Marine Intertidal Shingle and/or Pebble Shoreline and/or Beaches suitable non-breeding
Marine Intertidal Shingle and/or Pebble Shoreline and/or Beaches suitable breeding
Marine Intertidal Tidepools major breeding
Marine Neritic Macroalgal/Kelp major non-breeding
Marine Neritic Macroalgal/Kelp major breeding
Marine Neritic Pelagic suitable non-breeding
Marine Neritic Pelagic suitable breeding
Marine Neritic Seagrass (Submerged) major non-breeding
Marine Neritic Seagrass (Submerged) major breeding
Marine Neritic Subtidal Loose Rock/pebble/gravel major non-breeding
Marine Neritic Subtidal Loose Rock/pebble/gravel major breeding
Marine Neritic Subtidal Rock and Rocky Reefs major non-breeding
Marine Neritic Subtidal Rock and Rocky Reefs major breeding
Marine Neritic Subtidal Sandy major non-breeding
Marine Neritic Subtidal Sandy major breeding
Marine Neritic Subtidal Sandy-Mud major non-breeding
Marine Neritic Subtidal Sandy-Mud major breeding
Altitude 0 - 50 m Occasional altitudinal limits  

Threats & impact
Threat (level 1) Threat (level 2) Impact and Stresses
Biological resource use Fishing & harvesting aquatic resources - Unintentional effects: (large scale) [harvest] Timing Scope Severity Impact
Ongoing Majority (50-90%) Causing/Could cause fluctuations Medium Impact: 6
Stresses
Indirect ecosystem effects, Reduced reproductive success
Biological resource use Hunting & trapping terrestrial animals - Intentional use (species is the target) Timing Scope Severity Impact
Ongoing Minority (<50%) Negligible declines Low Impact: 4
Stresses
Reduced reproductive success, Species mortality
Climate change & severe weather Temperature extremes Timing Scope Severity Impact
Ongoing Majority (50-90%) Causing/Could cause fluctuations Medium Impact: 6
Stresses
Ecosystem degradation, Reduced reproductive success, Species mortality
Human intrusions & disturbance Recreational activities Timing Scope Severity Impact
Ongoing Majority (50-90%) Slow, Significant Declines Medium Impact: 6
Stresses
Species disturbance
Invasive and other problematic species, genes & diseases Invasive non-native/alien species/diseases - Mus musculus Timing Scope Severity Impact
Ongoing Minority (<50%) Slow, Significant Declines Low Impact: 5
Stresses
Reduced reproductive success
Invasive and other problematic species, genes & diseases Invasive non-native/alien species/diseases - Rattus rattus Timing Scope Severity Impact
Ongoing Minority (<50%) Slow, Significant Declines Low Impact: 5
Stresses
Reduced reproductive success
Pollution Industrial & military effluents - Type Unknown/Unrecorded Timing Scope Severity Impact
Ongoing Minority (<50%) Negligible declines Low Impact: 4
Stresses
Reduced reproductive success

Utilisation
Purpose Primary form used Life stage used Source Scale Level Timing
Pets/display animals, horticulture - - International Non-trivial Recent

Recommended citation
BirdLife International (2021) Species factsheet: Larus heermanni. Downloaded from http://www.birdlife.org on 04/12/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 04/12/2021.