Great Blue Heron Ardea herodias


Taxonomic note
McGuire et al. (2019) review in detail the status of the all-white taxon occidentalis, which although formerly given species status (‘Great White Heron’ [GWH]) has long been considered a subspecies of Great Blue Heron [GBH] Ardea herodias, in great part because the two taxa interbreed with regularity. However, given that the evidence points to assortative mating where possible, they conclude that occidentalis is indeed better treated as a species.

It is separated by diagnostic plumage (white vs. blue), behavior (mate choice and timing of mating) and habitat (saltwater-island vs. fresh/brackish water mainland).

There are, in fact, a few additional morphological considerations, with GWH having a shorter occipital plume but longer bill, tarsus and middle toe than GBH (supplementary material online with measurements not accessed). Applying the Tobias criteria to the situation, the taxonomic status of GWH involves a consideration of its

·       all-white vs grey/blue plumage (an exceptional difference: score 4);
·       shorter occipital plume (seemingly fairly distinctive from the authors’ Figure 3: allow 1);
·       longer tarsus (apparently the most distinctive of the longer characters measured, but perhaps insufficient to be allowed a score: ns);
·       timing of mating or habitat choice (only one of these permitted as a score: 1);
·       narrow hybrid zone (not more than 50 km as measured on Google Earth: 2).

On this basis BirdLife accepts Ardea occidentalis (Handbook of the Birds of the World and BirdLife International 2020) as a separate species.

Taxonomic source(s)
Handbook of the Birds of the World and BirdLife International. 2020. Handbook of the Birds of the World and BirdLife International digital checklist of the birds of the world. Version 5. Available at:

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

Red List history
Year Category Criteria
2020 Least Concern
Species attributes

Migratory status full migrant Forest dependency Low
Land mass type Average mass -

Estimate Data quality
Extent of Occurrence breeding/resident (km2) 14,500,000 medium
Extent of Occurrence non-breeding (km2) 32,000,000 medium
Number of locations -
Severely Fragmented -
Population and trend
Value Data quality Derivation Year of estimate
No. of mature individuals 500000-4999999 poor estimated 2019
Population trend Increasing estimated -
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) 8 - - -

Population justification: The population size of Great Blue Heron is estimated at 500,000-4,999,999 mature individuals (Partners in Flight 2019).

Trend justification: Although trends differ between populations, the species overall appears to be increasing slowly (Partners in Flight 2019, Wetlands International 2020). Trends have been quantified across North America, where the population has been growing at >10% in total since the 1960s (Meehan et al. 2018, Pardieck et al. 2018).

Country/territory distribution
Country/Territory Occurrence status Presence Resident Breeding Non-breeding Passage
Anguilla (to UK) N Extant
Antigua and Barbuda N Extant
Aruba (to Netherlands) N Extant
Bahamas N Extant
Barbados N Extant
Belize N Extant Yes
Bermuda (to UK) N Extant Yes
Bonaire, Sint Eustatius and Saba (to Netherlands) N Extant Yes
Brazil V Extant Yes
Canada N Extant Yes Yes
Cape Verde V Extant
Cayman Islands (to UK) N Extant
Colombia N Extant
Costa Rica N Extant Yes
Cuba N Extant
Curaçao (to Netherlands) N Extant Yes
Dominica N Extant
Dominican Republic N Extant
Ecuador N Extant
El Salvador N Extant
France V Extant
Greenland (to Denmark) V Extant
Grenada N Extant
Guadeloupe (to France) N Extant Yes
Guatemala N Extant
Haiti N Extant
Honduras N Extant
Jamaica N Extant Yes
Martinique (to France) N Extant
Mexico N Extant
Montserrat (to UK) N Extant
Nicaragua N Extant
Panama N Extant
Portugal V Extant
Puerto Rico (to USA) N Extant
Sint Maarten (to Netherlands) N Extant Yes
Spain V Extant
St Kitts and Nevis N Extant
St Lucia N Extant
St Martin (to France) N Extant Yes
St Pierre and Miquelon (to France) N Extant Yes
St Vincent and the Grenadines N Extant
Trinidad and Tobago N Extant
Turks and Caicos Islands (to UK) N Extant
United States Minor Outlying Islands (to USA) N Extant Yes
USA N Extant Yes
Venezuela N Extant
Virgin Islands (to UK) N Extant Yes
Virgin Islands (to USA) N Extant Yes

Important Bird and Biodiversity Areas (IBA)
Country/Territory IBA Name
Mexico Pantanos de Centla
Mexico Bahía de Ceuta - Cospita
Mexico Estero Cardonal
Mexico Cuenca baja del Río Papagayo
Mexico Presa de Valsequillo

Habitats & altitude
Habitat (level 1) Habitat (level 2) Importance Occurrence
Forest Subtropical/Tropical Mangrove Vegetation Above High Tide Level suitable breeding
Forest Subtropical/Tropical Mangrove Vegetation Above High Tide Level suitable non-breeding
Marine Intertidal Mud Flats and Salt Flats suitable breeding
Marine Intertidal Mud Flats and Salt Flats suitable non-breeding
Wetlands (inland) Bogs, Marshes, Swamps, Fens, Peatlands major breeding
Wetlands (inland) Permanent Freshwater Lakes (over 8ha) suitable breeding
Wetlands (inland) Permanent Rivers/Streams/Creeks (includes waterfalls) suitable breeding
Altitude 0 - 2600 m Occasional altitudinal limits  

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: Ardea herodias. Downloaded from on 21/09/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from on 21/09/2021.