Larus atlanticus

Taxonomy

Assessment Information

Geographic Range

Population

Habitat and Ecology

Threats

Conservation Actions

View Printer Friendly

Taxonomy [top]

Kingdom	Phylum	Class	Order	Family
ANIMALIA	CHORDATA	AVES	CHARADRIIFORMES	LARIDAE

Scientific Name:

Larus atlanticus

Species Authority:

Olrog, 1958

Common Name/s:

English

–

Olrog's Gull

Taxonomic Notes:

Assessment Information [top]

Red List Category & Criteria:

Vulnerable B1ab(ii,iii,v);C2a(i) ver 3.1

Year Published:

2012

Assessor/s:

BirdLife International

Reviewer/s:

Butchart, S. & Symes, A.

Contributor/s:

Azpiroz, A., García Borboroglu, P., Petracci, P. & Yorio, P.

Justification:
This species has a small range and population, both of which are likely to be undergoing a slow but continuous decline owing, in particular, to a variety of threats to its breeding grounds. It consequently qualifies as Vulnerable.

History:

2008	–	Vulnerable
2006	–	Vulnerable
2004	–	Vulnerable
2000	–	Vulnerable
1996	–	Vulnerable
1994	–	Vulnerable

Geographic Range [top]

Range Description:	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 (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 2007, P Yorio, P. García Borboroglu, and P. Petracci, unpubl. data). Over 98% of the total breeding population nests in south Buenos Aires province and 50-70% is concentrated in the Bahía Blanca estuary (P Yorio and P. García Borboroglu in litt. 2012), an area subject to growing human development (disturbance and pollution). In winter, the species disperses north, reaching Uruguay (Azpiroz in litt. 1999) and Brazil (Dias and Maurício 1998, Pacheco et al. 2009) recorded at eight localities in Rio Grande do Sul, mostly around Lagoa dos Patos (Pacheco et al. 2009), with one inland record in Córdoba (Yzurieta 1995). Also recently sighted for the first time in Santa Catarina, thereby extending its range 380km beyond Rio Grande do Sul, its previous most northerly location (Pacheco et al. 2009). Previously considered a vagrant to Brazil, it is currently considered a regular visitor in April-August (Pacheco et al. 2009). The world population has been estimated at 4,800-7,800 pairs (P Yorio, P. García Borboroglu, and P. Petracci, unpubl. data, 2012). Recent data reporting 3,800 active nests in 2005 indicate the population may be larger than previously thought and may exceed 10,000 individuals (R. Clay in litt. 2009). Radio telemetry indicates strong site fidelity in non-breeding areas (Berón et al. 2007).
Countries:	Native: Argentina; Brazil; Uruguay Present - origin uncertain: Chile
Range Map:	Click here to open the map viewer and explore range.

Population [top]

Population:	A count of 2,806 nests (8,418 individuals) was recorded in the Isla del Puerto colony in 2003. P. M. Yorio in litt. (2005) estimated 3,500 pairs in total, equating to 7,000 mature individuals and 10,500 individuals.
Population Trend:	Decreasing

Habitat and Ecology [top]

Habitat and Ecology:	Behaviour Olrog's Gull is a coastal species with a restricted range in south eastern South America. It is one of the few globally threatened Larus species. It 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). Habitat It breeds on flat islands on bare ground or close to low vegetation, and close to the high tide line (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. Diet The species depends mainly on three crab species (Neohelice granulata, Cyrtograpsus altimanus and C. angulatus) during the breeding season (Delhey et al. 2001, Herrera et al. 2005, Suárez, et al. 2011). During incubation N. granulata predominated in the diet (>90%) with C. altimus a minor component (<2% of crabs taken). However, during young chick rearing this was reversed, with C. altimus forming the bulk of diet (<10% v. 60%, respectively) (Suárez et al. 2011). During the winter, varunid crabs remain the main prey (proportionally made up of 70% N. granulata and 30% C. angulatus) (Berón and Favero 2010), but it also shows a more opportunistic feeding ecology consuming molluscs, snails, small fish, insects, garbage and fish discards (Spivak and Sanchez 1992, Martinez et al. 2000, Silva Rodriguez et al. 2005). At Isla Felipe, diet analysis showed that Cyrtograpsus altimanus contributed 76.1% of the diet and C. angulatus contributed 21.7% (Herrera et al. 2005). At Mar Chiquita Lagoon during the non-breeding season, grapsid crabs were by far the main prey in frequency of occurrence, followed by fish and snails (Copello and Favero 2001). 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. Foraging range At Golfo San Jorge, Argentina, breeding Olrog's Gulls fed almost exclusively within the inlet (Yorio et al. 2004). Feeding grounds were located up to 7 km from the colony, but 85% of mapped locations were within 3 km of the colony, near the mouth of the 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 only within the Caleta Malaspina, in an area of less than 35 sq km, and 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). The species has a small foraging range, defined by the spatial extension of intertidal habitats (Yorio et al. 2004). Since crabs are their main prey, particularly during the breeding season, they are dependent on intertidal areas with grapsid crabs (Martinez et al. 2000). Olrog's Gulls usually forage on open mudflats or along muddy intertidal areas with loose rocks and algae (Yorio et al. 2004), although it has also been observed to feed along a rocky shore where the presence of crabs was confirmed (Yorio et al. 2004). 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). At Mar del Plata harbour, Argentina, the species has frequently been observed to associate with commercial fishing activities (Martinez et al. 2000). 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).
Systems:	Terrestrial; Marine

Habitat and Ecology:

Behaviour Olrog's Gull is a coastal species with a restricted range in south eastern South America. It is one of the few globally threatened Larus species. It 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). Habitat It breeds on flat islands on bare ground or close to low vegetation, and close to the high tide line (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. Diet The species depends mainly on three crab species (Neohelice granulata, Cyrtograpsus altimanus and C. angulatus) during the breeding season (Delhey et al. 2001, Herrera et al. 2005, Suárez, et al. 2011). During incubation N. granulata predominated in the diet (>90%) with C. altimus a minor component (<2% of crabs taken). However, during young chick rearing this was reversed, with C. altimus forming the bulk of diet (<10% v. 60%, respectively) (Suárez et al. 2011). During the winter, varunid crabs remain the main prey (proportionally made up of 70% N. granulata and 30% C. angulatus) (Berón and Favero 2010), but it also shows a more opportunistic feeding ecology consuming molluscs, snails, small fish, insects, garbage and fish discards (Spivak and Sanchez 1992, Martinez et al. 2000, Silva Rodriguez et al. 2005). At Isla Felipe, diet analysis showed that Cyrtograpsus altimanus contributed 76.1% of the diet and C. angulatus contributed 21.7% (Herrera et al. 2005). At Mar Chiquita Lagoon during the non-breeding season, grapsid crabs were by far the main prey in frequency of occurrence, followed by fish and snails (Copello and Favero 2001). 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. Foraging range At Golfo San Jorge, Argentina, breeding Olrog's Gulls fed almost exclusively within the inlet (Yorio et al. 2004). Feeding grounds were located up to 7 km from the colony, but 85% of mapped locations were within 3 km of the colony, near the mouth of the 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 only within the Caleta Malaspina, in an area of less than 35 sq km, and 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). The species has a small foraging range, defined by the spatial extension of intertidal habitats (Yorio et al. 2004). Since crabs are their main prey, particularly during the breeding season, they are dependent on intertidal areas with grapsid crabs (Martinez et al. 2000). Olrog's Gulls usually forage on open mudflats or along muddy intertidal areas with loose rocks and algae (Yorio et al. 2004), although it has also been observed to feed along a rocky shore where the presence of crabs was confirmed (Yorio et al. 2004). 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). At Mar del Plata harbour, Argentina, the species has frequently been observed to associate with commercial fishing activities (Martinez et al. 2000). 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).

Systems:

Terrestrial; Marine

Threats [top]

Major Threat(s):	The Bahía Blanca estuary is subject to intense human pressure from urban development, industry, agriculture, recreation, fishing, and pollution with lead and other heavy metals found in tissue samples in 2007 (García Borboroglu and Yorio 2007a, Saggese et al. 2009). Human disturbance is thought to be an important factor in the low reproductive success of the species through destruction of nests and killing of chicks (Berón et al. 2007). Bahía Anegada is subject to recreational activities, artisanal fishing and ranching activites, and eggs at the colonies near Bahía San Blas are occasionally harvested (Yorio et al. 2005). Sports fisheries affect non-breeding birds in winter (Berón et al. 2005). They have frequently been observed associating with commercial fisheries at Mar del Plata harbour and are threatened by injestions of discarded hooks or entanglement with lines and nylon bags (Berón et al. 2007).

Major Threat(s):

The Bahía Blanca estuary is subject to intense human pressure from urban development, industry, agriculture, recreation, fishing, and pollution with lead and other heavy metals found in tissue samples in 2007 (García Borboroglu and Yorio 2007a, Saggese et al. 2009). Human disturbance is thought to be an important factor in the low reproductive success of the species through destruction of nests and killing of chicks (Berón et al. 2007). Bahía Anegada is subject to recreational activities, artisanal fishing and ranching activites, and eggs at the colonies near Bahía San Blas are occasionally harvested (Yorio et al. 2005). Sports fisheries affect non-breeding birds in winter (Berón et al. 2005). They have frequently been observed associating with commercial fisheries at Mar del Plata harbour and are threatened by injestions of discarded hooks or entanglement with lines and nylon bags (Berón et al. 2007).

Conservation Actions [top]

Conservation Actions:	Conservation Actions Underway CMS Appendix I. All colonies in southern Buenos Aires, except the largest one, Isla del Puerto, are included in two protected areas: the Bahía Blanca, Falsa and Verde Nature Reserve and the Bahía San Blas Nature Reserve. The colonies in southern Chubut have recently gained legal protection due to the designation of a new marine protected area in northern Golfo San Jorge, the Parque Interjurisdiccional Marino Costero Patagonia Austral. In winter, it has been recorded in numerous reserves (Chebez et al. 1998, A. B. Azpiroz in litt. 1999). In early December 2008 600 fledglings were colour-ringed by Aves Argentinas at Bahia Blanca, southern Buenos Aires province, with any sightings to be reported to Aves Argentinas to understand movement patterns (BirdLife International 2009). 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). Enlarge the Bahía Blanca, Falsa and Verde Nature Reserve to include the colony at Isla del Puerto (Yorio et al. 2005). 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 Olrog's gull populations in southern Buenos Aires (Yorio et al. 2005). 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).

Conservation Actions:

Conservation Actions Underway
CMS Appendix I. All colonies in southern Buenos Aires, except the largest one, Isla del Puerto, are included in two protected areas: the Bahía Blanca, Falsa and Verde Nature Reserve and the Bahía San Blas Nature Reserve. The colonies in southern Chubut have recently gained legal protection due to the designation of a new marine protected area in northern Golfo San Jorge, the Parque Interjurisdiccional Marino Costero Patagonia Austral. In winter, it has been recorded in numerous reserves (Chebez et al. 1998, A. B. Azpiroz in litt. 1999). In early December 2008 600 fledglings were colour-ringed by Aves Argentinas at Bahia Blanca, southern Buenos Aires province, with any sightings to be reported to Aves Argentinas to understand movement patterns (BirdLife International 2009).

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). Enlarge the Bahía Blanca, Falsa and Verde Nature Reserve to include the colony at Isla del Puerto (Yorio et al. 2005). 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 Olrog's gull populations in southern Buenos Aires (Yorio et al. 2005). 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).

Citation:	BirdLife International 2012. Larus atlanticus. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 24 May 2013.
Disclaimer:	To make use of this information, please check the <Terms of Use>.
Feedback:	If you see any errors or have any questions or suggestions on what is shown on this page, please fill in the feedback form so that we can correct or extend the information provided