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Olrog's Gull Larus atlanticus

  • Order: Charadriiformes
  • Family: Laridae
  • Monotypic
  • Authors: Pablo Yorio
Sections

Distribution

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Distribution of the Olrog's Gull
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eBird range map for Olrog's Gull

Generated from eBird observations (Year-Round, 1900-present)

Distribution in the Americas

The Olrog’s Gull is an endemic species to the Atlantic coasts of South America. It breeds only in Argentina between 38° 49´ and 45° 11´ S. There are currently fourteen colonies, 11 of which are distributed in the coastal sectors of Buenos Aires Province between the Bahía Blanca estuary and southern Bahía Anegada while three other are found in the north of Golfo San Jorge, Chubut, more than 700 km south of the Buenos Aires breeding grounds (Yorio et al. 2005, P. Yorio, P. García Borboroglu and P. Petracci, unpubl. Olrog's Gull colony at Bahía San Blas, Buenos Aires, Argentinadata). The Bahía Blanca estuary holds over 70% of the breeding population (Delhey and Petracci 2004). The number of recorded colonies and their location in each year has varied, as Olrog’s Gulls often change breeding locations between years (Yorio et al. 1997, García Borboroglu and Yorio 2007a). In the province of Buenos Aires, it has been recorded breeding in Isla del Puerto, Tres Brazas, Golfada Chica, Canal Ancla, Isla Trinidad (Islote Norte, Islote Bastón, Islote Redondo, Islote Sur), Isla Brightman, Islote Norte de Isla Morro de Indio, Isla Gaviota, Isla Puestos, Isla Gama, Banco Nordeste and Isla Arroyo Jabalí Oeste. In Chubut province, it has been recorded breeding at Islas Laguna (Islote Laguna and Islote Luisoni), Isla Felipe and Islas Vernaci (Isla Sudoeste, Isla Noroeste and Isla Oeste Noroeste).

In winter the species disperses north along the Atlantic and Río de la Plata coasts of Buenos Aires province (Favero 1991, Bo et al. 1995, Chebez and Yorio 2008), and reaches Uruguay (Escalante 1970, Aspiroz 2003) and Brazil (Díaz and Mauricio 1988, Sick 2001). There are accidental inland records in Mar Chiquita, Córdoba province (Yzurieta 1995, Torres and Michelutti, 2005). Although in Uruguay it is mainly a winter visitor, recorded from April up to December (Escalante 1984), some individuals have been sighted in summer (Wetlands International 2006, D. Caballero, pers. comm.). Similarly, birds of different age-classes can be found along the Buenos Aires coast throughout the year (Escalante 1966, Savigny and Favero 2005, Silva et al. 2005, Chébez and Yorio 2008). A detailed list of sighting locations and references can be found in Escalante (1984), Collar et al. (1992) and Chébez and Yorio (2008).

Distribution outside the Americas

Endemic to the Americas.

Habitat

Olrog' Gull nesting habitat on islands in southern Buenos AiresAll colonies are located on flat islands or islets and in close proximity to intertidal crab habitats (García Borboroglu and Yorio 2007a). Colonies are generally situated on open ground, close to the high tide line, and far from vegetation. In a few breeding locations, peripheral nests are found close to low herbaceous plants or shrub species (< 0.2–0.3 m) belonging to the genera Atriplex, Salicornia, Franquenia, Limonium, and Spartina. (Yorio et al. 2001a, García Borboroglu and Yorio 2007a). At Isla del Puerto, vegetation in the colony area consists of low bushes (< 0.5 m) of Allenrolfea patagonica, Heterostachys ritteriana, H. olivascens and Salicornia ambigua (Delhey et al. 2001b). When foraging, both during the breeding andCoastal areas with soft substrates and crab beds used by foraging Olrog's Gulls 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., in press). They have been also recorded in harbors, refuse tips, sewage outfalls or, rarely, at sea associated to fishing vessels (Jehl and Rumboll 1976, Martinez et al. 2000, Silva Rodríguez et al. 2005).

Historical changes

Olrog’s Gulls were first recorded nesting in Bahía San Blas, Argentina, in 1932 (Daguerre 1933), and subsequently was observed breeding in the same area in the 1963 (Olrog 1967) and 1975 (Devillers 1977). However, wide scale surveys and colony counts were not conducted until the 1990s (see review in Yorio et al. 2005). Due to their habit of changing breeding sites among seasons and lack of time series data it is not possible yet to detect population trends. However, information from the three colonies in Chubut suggests that at least in that coastal sector the population has remained stable during the last fifteen years (Yorio et al. 2005). Recently discovered new colonies and higher number of individuals in southern Buenos Aires very likely do not reflect a population increase but a more comprehensive survey of northern breeding grounds.

Fossil history

No information.

Recommended Citation

Yorio, P. (2009). Olrog's Gull (Larus atlanticus), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/nb.olrgul1.01