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Olrog's Gull Larus atlanticus

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

Appearance

Distinguishing Characteristics

Flying Olrog's Gull showing black sub terminal bandThe Olrog’s Gull is a large white-headed gull with black wings and a white tail with broad, black sub terminal band in adult plumage.

Similar Species

Non-flying adult and second year Olrog’s Gull might be confused with Kelp Gull Larus dominicanus (Howell and Dunn 2007). Kelp Gull is slightly larger with wholly white tail, no subterminal band on bill and white tips to primaries. Second year Kelp Gulls have a black tail band. The two species overlap in their breeding and wintering distributions, although Kelp Gull is much more broadly distributed. Kelp Gulls breed adjacent to all known Olrog’s Gull colonies (GarcĂ­a Borboroglu and Yorio 2007a), and share non-breeding areas.

Detailed Description

Adult Olrog's GullIt is a large, black-and-white gull, with white head, neck, and rump and under parts. The rest of upperparts are black. Black wings with white trailing edge. It has a white tail with broad, black sub terminal band which is more evident in birds in flight. The bill is relatively long and stout and the legs are relatively long. Juvenile is mostly brown with dark head and neck; dark tail. A detailed description of plumage variation as a function of age can be found in Howell and Dunn (2007).

Molts

Unknown.

Bare Parts

Yellow bill with black sub terminal band and red tipEyes are brown with red orbital ring. Bill is yellow with black sub terminal band and red tip. Legs are yellowish. The coloration of bare parts varies with age, and detailed descriptions can be found in Howell and Dunn (2007).

Measurements

Total body length is 50-60 cm and 130-140 wingspan (Escalante 1966, Petracci 2002, Howell and Dunn 2007). Males tend to be larger than females (Petracci 2002). Body measurements of breeding individuals in Chubut (Islas Vernaci) were as follows: bill length = 48.9 ± 1.5 mm, bill depth = 17.2 ± 0.7, head length = 10.5 ± 0.3, tarsus = 69.0 ± 3.9 (n = 8); weight = 810.0 ± 45.5 (n = 7). Measurements of museum specimens can be found in Escalante (1966) and Olrog (1967).

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