Grey-backed Tern Onychoprion lunatus


Taxonomic note
Onychoprion lunatus (del Hoyo and Collar 2014) was previously placed in the genus Sterna as S. lunata.

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
2018 Least Concern
2016 Least Concern
2012 Least Concern
2009 Least Concern
2008 Least Concern
2004 Least Concern
2000 Lower Risk/Least Concern
1994 Lower Risk/Least Concern
1988 Lower Risk/Least Concern
Species attributes

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

Estimate Data quality
Extent of Occurrence breeding/resident (km2) 29,100,000
Extent of Occurrence non-breeding (km2) 45,900,000
Number of locations -
Severely Fragmented -
Population and trend
Value Data quality Derivation Year of estimate
No. of mature individuals poor estimated 2009
Population trend Decreasing suspected -
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) 12 - - -

Population justification: The population is estimated at 100,000-1,000,000 individuals.

Trend justification: The population is suspected to be in decline owing to predation at breeding sites (del Hoyo et al. 1996).

Country/territory distribution
Country/Territory Occurrence status Presence Resident Breeding Non-breeding Passage
American Samoa N Extant Yes
Cook Islands U Extant
Fiji N Extant Yes
French Polynesia N Extant Yes
Indonesia N Extant Yes
Japan V Extant Yes
Kiribati N Extant Yes
Marshall Islands N Extant Yes
Micronesia, Federated States of N Extant Yes
Nauru U Extant
Niue (to New Zealand) U Extant
Northern Mariana Islands (to USA) N Extant Yes
Palau N Extant Yes
Papua New Guinea U Extant
Pitcairn Islands (to UK) U Extant
Samoa V Extant Yes
Solomon Islands N Extant Yes
Tokelau (to New Zealand) U Extant
Tonga U Extant
Tuvalu V Extant Yes
United States Minor Outlying Islands (to USA) N Extant Yes
USA N Extant Yes
Vanuatu U Extant
Wallis and Futuna Islands (to France) U Extant

Important Bird and Biodiversity Areas (IBA)
Country/Territory IBA Name
French Polynesia Hatu iti
French Polynesia Tetiaroa
Kiribati Malden Island
French Polynesia Manuae, Motu One et Maupihaa
Northern Mariana Islands (to USA) Guguan Island
Kiribati McKean Island
Kiribati Abariranga (Canton) Island
Kiribati Enderbury Island
Kiribati Rawaki (Phoenix Island)
Kiribati Kiritimati (Christmas Island)
American Samoa National Park of American Samoa - Tutuila
French Polynesia Vallée de Avera
USA Northwestern Hawaiian Islands
French Polynesia Tikehau
French Polynesia Hatuta'a
American Samoa Rose Atoll
French Polynesia Tahanea
Kiribati Starbuck Island
French Polynesia Ilots rocheux de Ua Huka
French Polynesia Ua Huka
French Polynesia Ilots rocheux de Ua Pou
French Polynesia Fakarava Atolls
French Polynesia Haraiki
French Polynesia Hatu iti
Marshall Islands Enewetok Atoll
Marshall Islands Bokak Atoll
Marshall Islands Bikar Atoll
United States Minor Outlying Islands (to USA) Wake Island
United States Minor Outlying Islands (to USA) Baker Island
United States Minor Outlying Islands (to USA) Howland Island
United States Minor Outlying Islands (to USA) Johnston Atoll
United States Minor Outlying Islands (to USA) Jarvis Island
Kiribati Phoenix Islands Marine
Northern Mariana Islands (to USA) Guguan Island Marine
Kiribati Malden Island Marine
Tokelau (to New Zealand) Atafu
Northern Mariana Islands (to USA) Uracus

Habitats & altitude
Habitat (level 1) Habitat (level 2) Importance Occurrence
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 major breeding
Marine Intertidal Shingle and/or Pebble Shoreline and/or Beaches major breeding
Marine Intertidal Tidepools major breeding
Marine Neritic Macroalgal/Kelp suitable resident
Marine Neritic Pelagic major non-breeding
Marine Neritic Seagrass (Submerged) suitable resident
Marine Neritic Subtidal Loose Rock/pebble/gravel suitable resident
Marine Neritic Subtidal Rock and Rocky Reefs suitable resident
Marine Neritic Subtidal Sandy suitable resident
Marine Neritic Subtidal Sandy-Mud suitable resident
Rocky areas (eg. inland cliffs, mountain peaks) suitable breeding
Altitude   Occasional altitudinal limits  

Threats & impact
Threat (level 1) Threat (level 2) Impact and Stresses
Invasive and other problematic species, genes & diseases Invasive non-native/alien species/diseases - Named species Timing Scope Severity Impact
Ongoing Minority (<50%) Rapid Declines Medium Impact: 6
Reduced reproductive success, Species mortality

Recommended citation
BirdLife International (2023) Species factsheet: Onychoprion lunatus. Downloaded from on 26/03/2023. Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from on 26/03/2023.