Olrog's Gulls Research Articles

Breeding Habitat Requirements and Selection by Olrog's Gull (Larus Atlanticus), A Threatened Species

AbstractWe studied habitat requirements and selection of Olrog's Gulls (Larus atlanticus) breeding at six colonies along 2,500 km of coastline in central Argentina that encompasses its entire distributional range. Colonies were located only on islands that ranged in size between 0.4 and 125.8 ha, and the islands' distance to the mainland varied from 0.12 to 16.7 km. Colonies ranged in size between 12 and 341 nests. In three of the colonies, gulls nested in subcolonies (range: 8–239 nests). They nested at relatively high densities, with a mean inter-nest distance of 0.66 ± 0.25 m. Logistic regression analysis to compare nest and random-site characteristics at each colony showed that Olrog's Gulls selected sites that were close to the high-tide line, at a lower height above sea level, far from available vegetation, and had lower vegetation cover over the nest. Olrog's Gulls showed a significant positive association with Kelp Gulls (L. dominicanus), an expanding generalist species that also nests in similar habitats. Current trends in coastal development, particularly in the Olrog's Gulls' main breeding grounds of southern Buenos Aires, indicate the urgent need for habitat-protection guidelines for this threatened species. Moreover, its breeding association with Kelp Gulls suggests a potential spatial conflict and highlights the need for increased monitoring and management actions.Selección y Requerimientos de Hábitat Reproductivo en Larus atlanticus, una Especie Amenazada

Intestinal Acanthocephaladiosis in Olrog's Gulls (Larus atlanticus): Profilicollis chasmagnathi as Possible Cause of Death

In 2003 and 2005, mortality events were observed among hatch-year Olrog's gulls (Larus atlanticus) in a breeding colony in the Bahía Blanca estuary, Argentina. Freshly dead chicks were collected for parasitologic and parasite-associated pathologic studies. Profilicollis chasmagnathi was found at various intensities in all of the birds examined (n=28). On gross and histopathologic examinations, severe lesions ranging from intestinal obstruction to complete perforation were present in small and large intestines of the birds. Larval forms of P. chasmagnathi were being found in prey items of L. atlanticus in the study area, which suggests that diet may play a central role in the epidemiology of disease and mortality events in this species.

BREEDING HABITAT REQUIREMENTS AND SELECTION BY OLROG'S GULL (LARUS ATLANTICUS), A THREATENED SPECIES

Abstract We studied habitat requirements and selection of Olrog's Gulls (Larus atlanticus) breeding at six colonies along 2,500 km of coastline in central Argentina that encompasses its entire distributional range. Colonies were located only on islands that ranged in size between 0.4 and 125.8 ha, and the islands' distance to the mainland varied from 0.12 to 16.7 km. Colonies ranged in size between 12 and 341 nests. In three of the colonies, gulls nested in subcolonies (range: 8–239 nests). They nested at relatively high densities, with a mean inter-nest distance of 0.66 ± 0.25 m. Logistic regression analysis to compare nest and random-site characteristics at each colony showed that Olrog's Gulls selected sites that were close to the high-tide line, at a lower height above sea level, far from available vegetation, and had lower vegetation cover over the nest. Olrog's Gulls showed a significant positive association with Kelp Gulls (L. dominicanus), an expanding generalist species that also nests in similar...

Diet specialization of Olrog's Gull Larus atlanticus during the breeding season at Golfo San Jorge, Argentina

We studied the diet of breeding Olrog's Gulls Larus atlanticus during 1994 at two colonies in Golfo San Jorge, Argentina, through the analysis of 207 regurgitated pellets. The diet at Isla Felipe and Isla Vernaci Sudoeste comprised only a few items (9 vs 7 respectively), of which crabs were the main component. At Isla Felipe, the crabs Cyrtograpsus altimanus and C. angulatus were present in 91.2% and 89.2% of pellets, respectively, while the percentage contribution of each species was 76.1% and 21.7%, respectively. At Isla Vernaci Sudoeste, the figures were similar (96.2% and 80% of pellets, and percentage contributions 79.4% and 19.5%). All other taxa were present in less than 11% of pellets. No significant differences were found between colonies in the number of prey items, prey individuals per pellet, and consumption of crabs. Percentage contribution of crabs differed significantly between stages of the breeding cycle at Isla Felipe but not at Isla Vernaci Sudoeste. At both colonies, the proportion of male C. altimanus in pellets was larger than that of females. The proportion of female C. angulatus in pellets at Isla Vernaci Sudoeste was larger than that of males, but no significant differences were found in the consumption of each sex at Isla Felipe. Mean maximum carapace width of male crabs in pellets was not significantly different from that of females at either Isla Felipe or Isla Vernaci. Our study at Golfo San Jorge confirms that Olrog's Gull is fairly specialized, feeding mainly on crabs during the breeding season.

Olrog's Gull Larus atlanticus: specialist or generalist?

A study was made of the feeding behaviour of Olrog's gull Larus atlanticus in winter. Although feeding mainly on crabs they also, contrary to previous observations, made use of discarded offal, much as other species of gull. Such generalist feeding habits are likely to be beneficial to the conservation of the species.