Olrog’s gull (Larus atlanticus)

Synonyms: Larus belcheri atlanticus
KingdomAnimalia
PhylumChordata
ClassAves
OrderCharadriiformes
FamilyLaridae
GenusLarus (1)
SizeLength: 50 – 56 cm (2)

Olrog’s gull is classified as Vulnerable (VU B1ab(iii,v); C2a(i)) on the IUCN Red List 2004 (1) and is listed on Appendix I of the Convention on Migratory Species (CMS or Bonn Convention) (3).

This large gull has a white head, neck, rump and underside, with black wings and a black band on the tail. The legs and bill are yellow, and the bill has a black band near the end, with a red tip. Outside the breeding season, the gull’s colouration becomes mottled on the head. Juveniles are brown and also have mottled heads. They have a dark tail and a black tip to their bills, rather than the mature red tip. This species has nasal and rasping calls (2).

Olrog’s gull breeds on the Argentinean coast in eight distinct colonies. It spends the winter further north in Uruguay and Brazil (2).

Breeding on low-level sandy islands, Olrog’s gull inhabits areas with beaches, rocky coasts, harbours, and brackish lagoons and estuaries (2).

Olrog’s gull nests in colonies of between 12 and 400 pairs, mating from September. Nests vary from a simple scrape lined with vegetation to raised platforms of twigs and plants, in amongst glasswort (Salicornia spp.) and grass tussocks. They are often far from the high tide line and can be very tightly packed together. Females lay between two and three eggs, and once the young have fledged the population disperses from the breeding site (5).

Touring the shoreline and swimming among reeds in the shallows, Olrog’s gull feeds mainly on crabs and mussels as well as fish and offal. It may also hover over the surface of the water and drop onto passing prey (5).

A large proportion of the breeding population is found at the Bahía Blanca estuary, where urban development, industry, agriculture, recreation, fishing and pollution all threaten their existence. Two breeding colonies have recently been abandoned for these reasons, as well as due to the construction of an airstrip. Commercial fisheries and petrol pollution threaten non-breeding birds (2).

Although the Bahía Blanca estuary colonies are within a reserve protection is barely enforced, and their feeding sites are not included in the protected area. The Bahía Blanca reserve must be enlarged to make it worthwhile, and sustainable management plans must be introduced. However, during the winter, however, they occupy numerous reserves. Oil companies and governments must still work to improve and enforce regulations controlling pollution levels (2).

For further information on this species see:

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  1. IUCN Red List (April, 2005)
    http://www.redlist.org
  2. BirdLife International (April, 2005)
    http://www.birdlife.org/datazone/search/species_search.html?action=SpcHTMDetails.asp&sid=3210&m=0
  3. CMS (April, 2005)
    http://www.cms.int
  4. Sargatal, J., Elliott, A. and Del Hoyo, J. (1992) Handbook of the Birds of the World Volume 3 Hoatzin to Auks. Lynx Edicions, Barcelona.