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Olrog's Gull Larus atlanticus
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This species has a highly restricted breeding range at a small number of colonies. Numbers breeding annually appear to fluctuate, but there is currently no evidence of a continuing decline, therefore the species has been reclassified as Near Threatened. Potential threats to breeding sites remain, and any evidence of declines would result in reclassification in a higher threat category.

Taxonomic source(s)
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.
SACC. 2006. A classification of the bird species of South America. Available at: #

Taxonomic note

50-56 cm. Large, black-and-white gull. White head, neck, rump and underparts. Rest of upperparts black. Black wings with white trailing edge. White tail with broad, black subterminal band. Yellowish legs. Yellow bill with black subterminal band and red tip. Juvenile mostly brown with dark mottling around head, dark tail and black bill tip. Similar spp. Kelp Gull L. dominicanus is slightly larger with wholly white tail, no subterminal band on bill and white tips to primaries. Voice Nasal and guttural calls.

Distribution and population
Larus atlanticus breeds on the coast of Argentina between 38º49’and 45°11'S (Yorio et al. 2005). It has been recorded breeding at eighteen coastal locations in the Bahía Blanca estuary and Bahía Anegada, south Buenos Aires, and north of Golfo San Jorge, Chubut, although there may be fewer than a dozen active nesting sites in any one year (Yorio et al. 1997, Yorio et al. 1999, P Yorio, P. García Borboroglu and P. Petracci, unpubl. data). The number of recorded colonies in each year has varied as it often changes breeding locations between years (Yorio et al. 1997, García Borboroglu and Yorio 2007a, Yorio et al. in press). Over 98% of the total breeding population nests in southern Buenos Aires province and between 50-70% is concentrated in the Bahía Blanca estuary, an area subject to growing human development (disturbance and pollution). In winter, the species disperses north, reaching Uruguay (Escalante 1970, Aspiroz 2003) and Brazil (Dias and Maurício 1998, Pacheco et al. 2009), with one inland record in Córdoba (Yzurieta 1995). The world population is currently estimated at  4,800-7,800 pairs (P Yorio, P. García Borboroglu, and P. Petracci, unpubl. data).

Population justification
The breeding population is variable between years, with the total number of nests estimated at 4,860 pairs in 2004, 7,790 pairs in 2007 and 5,240 in 2009 (Yorio et al. in press), roughly equating to 15,600 mature individuals. The largest colony recorded is Isla del Puerto, with between 1,635 and 3,800 nests depending on the year (Petracci et al. 2008, Yorio et al. in press).

Trend justification
The apparent population increase most likely reflects a more comprehensive simultaneous survey, and the variability between years in the observed total nesting population is over 20%, indicating the uncertainty involved and showing the difficulty in defining trends. Nevertheless, despite growing pressures at key breeding sites there is no current evidence that the population is declining.

Behaviour Olrog's Gull is a coastal species and is a specialist predator, feeding mainly on crabs, which may be the result of interference competition with the larger and behaviourally dominant Kelp Gull (Larus dominicanus) (Delhey et al. 2001b). Olrog's Gull is spatially associated with the Kelp Gull throughout its breeding range (Yorio et al. 1997). Olrog’s and Kelp gulls share several nesting microhabitat characteristics, so an increase in the area occupied by Kelp Gulls or in their nesting density as a result of their increase in numbers could affect the availability of adequate nesting habitats for Olrog’s Gulls (García-Borboroglu and Yorio 2007b). Kelp Gulls were also recorded preying upon Olrog’s Gull chicks at the Isla del Puerto colony (La Sala and Martorelli 2009).

Habitat It breeds on flat islands on bare ground or close to low vegetation, and close to the high tide line (Yorio et al. 2001, García Borboroglu and Yorio 2007a), and frequents beaches, rocky coasts, harbours, coastal and brackish lagoons and estuaries. Eggs are laid in September-October and chicks fledge in November or December (Yorio et al. 2005, La Sala et al. 2011).

Diet The species depends mainly on three crab species (Chasmagnathus granulata, Cyrtograpsus altimanus and C. angulatus) during the breeding season (Delhey et al. 2001, Herrera et al. 2005, Suárez, et al. 2011). During the winter, it feeds also on crabs but shows a more opportunistic feeding ecology consuming molluscs, snails, small fish, insects, grains, garbage and fish discards (Spivak and Sanchez 1992, Copello and Favero 2001, Delhey et al. 2001, Martinez et al. 2000, Berón et al. 2003, Silva Rodriguez et al. 2005, Berón et al. 2007, Petracci et al. 2007, Berón et al. 2001). At Mar Chiquita Lagoon during the non-breeding season, some differences in diet were found between ages, particularly in spring when mature birds start to feed on the eggs of ovigerous females of Cyrtograpsus angulatus (Copello and Favero 2001).

Foraging range
At Bahía San Blas, breeding Olrog’s Gulls gulls foraged mainly in three sectors located between 1.5 and 7 km north of the colony, although they can forage up to 30 km from the colony (Suárez et al. 2012, N. Suárez and P. Yorio, unpubl. data). At Golfo San Jorge, Argentina, feeding grounds of breeding Olrog’s Gulls were located up to 7 km from the colony, but 85% of mapped locations were within 3 km of the colony, almost exclusively within the Caleta Malaspina inlet (Yorio et al. 2004). The birds were consistent in the use of one particular area, and most birds foraged mainly in one or two areas (Yorio et al. 2004). Gulls foraged at all states of the tide, although they were more likely to forage during mid and low tides (Yorio et al. 2004). Non-breeding birds also show strong foraging site fidelity (Beron et al. 2007). When foraging, both during the breeding and non-breeding season, gulls are generally found along estuarine environments, brackish lagoons and open coastal areas with soft or rocky substrates, usually with presence of crabs (Escalante 1984, Favero et al. 2001, Silva Rodríguez et al. 2005, Yorio et al. 2004, Gatto et al. 2008, Suárez et al. 2012). In Argentina, it was observed to forage in crab-bed patches and beaches where sport-fishing activities usually took place (Beron et al. 2007). Individuals occasionally moved up to 4 km south to a village where they might also take advantage of rocky intertidal pools available along the shore (Beron et al. 2007). They have been also recorded in harbors, refuse tips, sewage outfalls or, rarely, at sea associated to fishing vessels (Martinez et al. 2000, Silva Rodríguez et al. 2005).. Similarly, in Mar Chiquita coastal lagoon, juveniles have often been observed making use of sport-fishing by-products (Copello and Favero 2001, Berón et al. 2007).

The Bahía Blanca estuary includes the city of Bahía Blanca, with over 400,000 inhabitants, and includes oil refineries, petrochemical industries, plastic factories, and pre-treated sewage outfalls which are important sources of pollutants (Marcovecchio 2000, Freije and Marcovecchio 2004). Recent studies at the Isla del Puerto colony have shown the potential negative effects of mercury pollution on breeding Olrog’s Gulls (La Sala et al. 2011). There are ongoing plans to dredge the main navigation channel in the Bahía Blanca estuary and deposit dredged materials in coastal sectors regularly used as foraging grounds by Olrog’s Gulls (P. Petracci, pers. comm to P. Yorio and P. Garcia Borboroglu). Growing economic activities that take place in the Bahía San Blas area include sports fishing, oyster harvesting, recreation, and tourism (Zalba et al. 2008). These activities temporally overlap with the Olrog’s Gull breeding season, as they are mostly concentrated in the spring and summer, and may directly affect gulls through disturbance at the nesting sites, the interruption of their normal foraging activities or indirectly through habitat modification. In Uruguay many coastal sites where the species occurs in the non-breeding season have deteriorated due to the loss of adjacent wetlands through urbanisation and industrial pollution (D. Caballero-Sadi in litt. 2013).

Conservation Actions Underway
CMS Appendix I. All colonies in southern Buenos Aires, except Isla Brightman, are included in protected areas. The Bahía Blanca, Falsa and Verde Nature Reserve and the Bahía San Blas Nature Reserve protect twelve of the breeding locations reported in the last twenty years. Isla del Puerto was designated as a protected area in 2011 (Reserva Natural Integral Islote del Puerto; Provincial Decree 469). The colonies in southern Chubut gained legal protection in 2009 due to the designation of a new marine protected area in northern Golfo San Jorge, the Parque Interjurisdiccional Marino Costero Patagonia Austral (Law 26446). In winter, it has been recorded in numerous reserves (Chebez et al. 1998, Chebez and Yorio 2008, A. B. Azpiroz in litt. 1999).
Conservation Actions Proposed
Given the frequent change in colony location of the species, develop comprehensive and simultaneous surveys throughout the breeding range during the same breeding season so as to obtain a correct estimation of the total breeding population (Yorio et al. 2005). Monitor the population (Yorio et al. 1997). Integrate management plans and actions through formal cooperative programmes (Yorio et al. 1999). Work with oil companies and governments to improve and enforce anti-pollution regulations (Yorio et al. 1999). Develop joint conservation actions between Argentina and Uruguay within the current framework of international agreements (Yorio et al. 2005). Evaluate natural and human related factors which may contribute to the observed changes between seasons in the use of colony sites (Yorio et al. 2005). Promote studies on the effects of pollution on populations in southern Buenos Aires (Yorio et al. 2005). Implement actions to eliminate egg harvesting and to minimize the negative impact of sport fisheries on non-breeding gulls. Implement monitoring programmes for the expanding Kelp Gull population and studies of behavioural interactions with Olrog's Gull (García Borboroglu and Yorio 2007b). Include non-breeding areas in conservation strategies, for example by creating areas to protect the species at the important Mar Chiquita, Buenos Aires province (Berón et al. 2007).

Azpiroz, A. B. 2003. Aves del Uruguay. Lista e introducción a su biología y conservación. Aves Uruguay-GUPECA, Montevideo, Uruguay.

Berón, M. P. 2003. Dieta de juveniles de Gaviota Cangrejera (Larus atlanticus) en estuarios de la provincia de Buenos Aires. Hornero 18(2): 113-117.

Berón, M. P.; Arias, A.; Favero, M. 2005. Mortalidad incidental en Gaviota de Olrog (Larus atlanticus) asociada a la pesquería deportiva en la Provincia de Buenos Aires.

Berón, M. P.; Favero, M. 2009. Mortality and injuries of Olrog"s Gull Larus atlanticus individuals associated with sport fishing activities in Mar Chiquita coastal lagoon, Buenos Aires Province. El Hornero 24: 99-102.

Berón, M. P.; Favero, M. 2010. Monitoreo de la dieta de la Gaviota de Olrog (Larus atlanticus) en la Laguna Mar Chiquita (Buenos Aires, Argentina) durante el período no reproductivo. Ornitologia Neotropical 21(2): 215-224.

Berón, M. P.; Favero, M.; Laich, A. G. 2007. Use of natural and anthropogenic resources by Olrog"s Gull Larus atlanticus: implications for the conservation of the species in non-breeding habitats. Bird Conservation International 17(4): 351-357.

Berón, M. P.; García, G. O.; Luppi, T.; Favero, M. 2011. Age-related prey selectivity and foraging efficiency of Olrog"s Gulls (Larus atlanticus). Emu 111: 172-178.

Chebez, J. C. 2008. Los que se van. Fauna Argentina amenazada. 2. Aves. Editorial Albatros Saci, Buenos Aires.

Chebez, J. C.; Rey, N. R.; Barbaskas, M.; Di Giacomo, A. G. 1998. Las aves de los Parques Nacionales de la Argentina. Literature of Latin America, Buenos Aries.

Collar, N. J.; Gonzaga, L. P.; Krabbe, N.; Madroño Nieto, A.; Naranjo, L. G.; Parker, T. A.; Wege, D. C. 1992. Threatened birds of the Americas: the ICBP/IUCN Red Data Book. International Council for Bird Preservation, Cambridge, U.K.

Copello, S. and Favero, M. 2001. Foraging ecology of Olrog's gull Larus atlanticus in Mar Chiquita Lagoon (Buenos Aires, Argentina): are there age-related differences? Bird Conservation International 11(3): 175-188.

Delany, S.; Scott, D. 2006. Waterbird population estimates. Wetlands International, Wageningen, The Netherlands.

Delhey, J. K. V.; Carrete, M.; Martínez, M. M. 2001. Diet and feeding dehaviour of Olrog's Gull Larus atlanticus in Bahia Blanca, Argentina. Ardea 89: 319-329.

Delhey, J. K.; Petracci, P. F.; Grassini, C. M. 2001. Hallazgo de una nueva colonia de la Gaviota de Olrog (Larus atlanticus) en la Ría de Bahía Blanca, Argentina. Hornero 16: 39-42.

Dias, R. A.; Maurício, G. N. 1998. Lista preliminar da avifauna da extremidade sudoeste do saco de Mangueira e arresdores, Rio Grande, Rio Grande do Sul. Atualidades Ornitológicas 86: 10-11.

Escalante, R. 1984. Problemas en la conservacion de dos poblaciones de laridos sobre la costa Atlantica de Sud America (Larus (belcheri) atlanticus y Sterna maxima). Revista del Museo Argentino de Ciencias Naturales "Bernadino Rivadavia" e Instituto nacional de Investigacion de las Ciencias Naturales. Zoologia 13(14): 147-152.

Freije, R. H. and Marcovecchio, J. E. 2004. Oceanografía química del estuario de Bahía Blanca. In: M. C. Piccolo; M. Hoffmeyer (ed.), El ecosistema del estuario de Bahía Blanca. Bahía Blanca, Argentina, pp. 69-78. IADO.

García Borboroglu, P.; Yorio, P. 2007. Breeding habitat requirements and selection by Olrog’s Gull (Larus atlanticus), a threatened species. The Auk 124: 1201-1212.

García Borboroglu, P.; Yorio, P. 2007. Comparative habitat use by syntopic Kelp Gulls (Larus dominicanus) and Olrog’s Gulls (L. atlanticus) in coastal Patagonia. Emu 107: 321-326.

Gatto, A.; Quintana, F.; Yorio, P. 2008. Feeding behavior and habitat use in a waterbird assemblage at a marine wetland in coastal Patagonia, Argentina. Waterbirds 31: 463-471.

Herrera, G.; G. Punta, G.; Yorio, P. 2005. Diet specialization of Olrog´s Gull Larus atlanticus during the breeding season at Golfo San Jorge, Argentina. Bird Conservation International 15: 89-97.

La Sala, L. F.; Petracci, P. F.; Smits, J. E.; Botté, S; Furness, R. W. 2011. Mercury levels and health parameters in the threatened Olrog"s Gull (Larus atlanticus) from Argentina. Environ. Monit. Assess. 181: 1-11.

La Sala, L.; Martorelli, S. 2010. First report of Olrog"s Gull depredation by sympatric Kelp Gulls. Wilson Journal of Ornithology 122: 188-189.

Marcovecchio, J. E. 2000. Land-based sources and activities affecting the marine environment at the Upper Southwestern Atlantic Ocean: an overview. UNEP Regional Seas Reports & Studies 170: 67.

Martinez, M. M.; Isacch, J. P.; Rojas, M. 2000. Olrog's Gull Larus atlanticus: specialist or generalist? Bird Conservation International 10: 89-92.

Pacheco, J. F.; Branco, J. O.; Piacentini, V. de Q. 2009. Olrog's Gull Larus atlanticus in Santa Catarina, Brazil: northernmost occurrence and first state record. Cotinga: 149-150.

Petracci P. F.; Delhey, K.; Sotelo, M. 2007. Hbitos granívoros en la Gaviota Cangrejera (Larus atlanticus): implicancias sobre su estatus de especialista. El Hornero 22: 51-54.

Petracci, P. F.; La Sala, L. F.; Aguerre, G.; Perez, C.H.; Acosta, N.; Sotelo, M.; Pamparana, C. 2004. Dieta de la Gaviota Cocinera (Larus dominicanus) durante el periodo reproductivo en el estuario de Bahia Blanca, Buenos Aires, Argentina. Hornero 19: 23-28.

Petracci, P. F.; Sotelo, M. R.; Díaz, L. I. 2008. Nuevo registro de nidificación de la Gaviota Cangrejera (Larus atlanticus) en la Reserva Natural Bahía Blanca, Bahía Falsa y Bahía Verde, Buenos Aires, Argentina. El Hornero 23: 37-40.

Saggese, M.D.; Quaglia, A.; Lambertucci, S. A.; Bo, M. S.; Sarasola, J. H.; Pereyra- Lobos, R.; Maceda, J. J. 2009. Survey of lead toxicosis in free-ranging raptors from central Argentina. In: Watson, R.T; Fuller, M.; Pokras, M.; Hunt, W. G. (ed.), Ingestion of spent lead ammunition: implications for wildlife and humans , pp. 1-9. The Peregrine Fund , Boise, Idaho.

Silva Rodríguez, M. P.; Favero, M.; Berón, M. P.; Mariano-Jelicich, R.; Mauco, L. 2005. Ecología y conservación de aves marinas que utilizan el litoral bonaerense como área de invernada. Hornero 20: 111-130.

Spivak, E. D.; Sánchez, N. 1992. Prey selection by Larus belcheri atlanticus in Mar Chiquita lagoon, Buenos Aires, Argentina: A posible explanation for its discontinuos distribution. Revista Chilena de Historia Natural 65: 209-220.

Suárez, N.; Retana, M. V.; Yorio, P. 2011. Temoral changes in diet and prey selection in the Threatened Olrog's Gull Larus atlanticus breeding in southern Buenos Aires, Argentina. Ardeola 58(1): 35-47.

Yorio, P.; Bertellotti, M.; Borboroglu, P. G. 2005. Estado poblacional y de conservación de gaviotas que se reproducen en el litoral marítimo Argentino. Hornero 20(1): 53-74.

Yorio, P.; Frere, E.; Gandini, P.; Conway, W. 1999. Status and conservation of seabirds breeding in Argentina. Bird Conservation International 9: 299-314.

Yorio, P.; Petracci, P.; Garcia Borboroglu, P. in press. Current status of the threatened Olrog"s Gull Larus atlanticus: global population, breeding distribution and threats. Bird Conservation International FirstView Article pp 1-10

Yorio, P.; Punta, G.; Rabano, D.; Rabuffetti, F.; Herrera, G.; Saravia, J.; Friedrich, P. 1997. Newly discovered breeding sites of Olrog's Gull Larus atlanticus in Argentina. Bird Conservation International 7: 161-165.

Yorio, P.; Rabano, D.; Friedrich, P. 2001b. Habitat and nest site characteristics of Olrog"s Gull Larus atlanticus breeding at Bahía San Blas, Argentina. Bird Conservation International 11: 27-34.

Yzurieta, D. 1995. Manual de reconocimiento y evaluacion ecologica de las aves de Córdoba. Ministerio de Agricultura, Ganaderia y Recursos Renovables, Córdoba.

Further web sources of information
Detailed species account from the Threatened birds of the Americas: the BirdLife International Red Data Book (BirdLife International 1992). Please note taxonomic treatment and IUCN Red List category may have changed since publication.

Detailed species account from the Threatened birds of the Americas: the BirdLife International Red Data Book (BirdLife International 1992). Please note, taxonomic treatment and IUCN Red List category may have changed since publication.

Explore HBW Alive for further information on this species

Recuento detallado de la especie tomado del libro Aves Amenazadas de las Americas, Libro Rojo de BirdLife International (BirdLife International 1992). Nota: la taxonomoía y la categoría de la Lista Roja de la UICN pudo haber cambiado desde esta publicación.

Search for photos and videos, and hear sounds of this species from the Internet Bird Collection

Text account compilers
Benstead, P., Capper, D., Harding, M., Hatchett, J., Lascelles, B., Pilgrim, J., Sharpe, C J, Symes, A. & Anderson, O.

Azpiroz, A., García Borboroglu, P., Petracci, P., Yorio, P. & Caballero Sadi, D.

Recommended citation
BirdLife International (2016) Species factsheet: Larus atlanticus. Downloaded from on 25/10/2016. Recommended citation for factsheets for more than one species: BirdLife International (2016) IUCN Red List for birds. Downloaded from on 25/10/2016.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.

Additional resources for this species

ARKive species - Olrog’s gull (Larus atlanticus) 0

Key facts
Current IUCN Red List category Near Threatened
Family Laridae (Gulls, Terns, Skimmers)
Species name author Olrog, 1958
Population size 9800-15600 mature individuals
Population trend Stable
Distribution size (breeding/resident) -
Country endemic? No
Links to further information
- Additional Information on this species