Germán O. García

Age-related prey selectivity and foraging efficiency of Olrog's Gulls (Larus atlanticus) feeding on crabs in their non-breeding grounds

Abstract Foraging ecology is an essential component of the life history of a species and a good understanding of foraging ecology is especially important for threatened species where prey populations may be adversely affected by anthropogenic processes. This study examines age-related prey selection and prey-handling efficiency of Olrogs Gulls (Larus atlanticus) during the non-breeding season at the Mar Chiquita Coastal Lagoon, Argentina. Foraging behaviour and diet were determined by focal observation and compared with the availability of prey within their foraging patches. All captured prey were crabs, with the Burrowing Crab (Neohelice granulata) more commonly taken than the Mud Crab (Cyrtograpsus angulatus). Gulls consumed small and medium-sized crabs in higher proportions than those available and consumed more male crabs. Juvenile Gulls had longer handling times than older birds. Handling times increased with size of crabs independently of the sex of prey. The handling efficiency of adults was significantly higher than that of subadults, which in turn was higher than that of juveniles. These differences between age-classes could be attributed to differential foraging skills and social subordination of juvenile Gulls. The reasons for avoidance of large crabs is not certain but might be because carapaces are not easily digested, there is a higher risk of injury, or capture of large crabs may result in more intense kleptoparasitic interactions, among others.

Foraging behaviour and diet of American Oystercatchers in a Patagonian intertidal area affected by nutrient loading

Abstract Eutrophication increases the biomass of opportunistic green macroalgae that covers intertidal zones, and macroalgal blooms may affect the intertidal invertebrate community and predation of invertebrates by shorebirds. In San Antonio Bay, Argentina, eutrophication from the discharge of wastewater from a coastal town produces periodic macroalgal blooms. Our aim was to assess if macroalgal blooms affect the foraging behaviour and diet of the American Oystercatcher (Haematopus palliatus). A macroalgal transplant experiment was performed in order to evaluate how epifaunal species respond to a macroalgal canopy. The availability of prey for Oystercatchers, and their foraging behaviour and diet, were analysed in two paired channels with different nutrient loadings. Oystercatchers generally ate the most profitable prey and avoided prey with a profitability value lower than the mean rate of energy intake. During the macroalgal blooms, Oystercatchers avoided two prey species with high profitability values, shifting their foraging strategy and feeding onto a suboptimal prey but with a high encounter rate. Our results suggest that nutrient loadings and the macroalgal blooms that they generate have effects on the diet and foraging behaviour of Oystercatchers, which results in an increase of the average rate of energy intake of Oystercatchers foraging along the channel subject to a macroalgal bloom.

Diversidad de Tetrápodos en un mosaico de ambientes del sudeste de la ecorregión Pampeana como herramienta para planificar en conservación

A pesar del avance en el conocimiento de la biodiversidad para ciertas regiones, este se encuentra en general disperso y no ha sido interpretado respecto a sus propiedades emergentes ni puesto en contextos que faciliten la toma de decisiones en conservacion. El sudeste de la ecorregion Pampas presenta una diversidad ambiental destacada en un area relativamente restringida, y existe ademas una importante cantidad de informacion sobre diversidad de Tetrapodos. Nuestro objetivo fue compilar y analizar este cumulo de informacion, a traves de una lista de especies con sus abundancias relativas por ambientes destacando aquellas endemicas y de interes para la conservacion. Evaluamos la complementariedad entre los taxa (anfibios, reptiles, aves y mamiferos) en terminos de composicion, numero de especies totales y amenazadas. La diversidad de Tetrapodos recopilada pone de manifiesto que esta pequena area presenta una importante riqueza de especies (12 especies de anfibios, 26 reptiles, 233 aves, 34 mamiferos; 41 estan amenazadas y tres son endemicas). Los ambientes representados (pastizales, dunas, sierras, humedales, estuarios, marino, agroecosistemas, urbanizaciones) contribuyen diferencialmente a la diversidad general de Tetrapodos. La distribucion desproporcionada de la riqueza de especies, de especies amenazadas y de la composicion entre ambientes dentro de cada taxon, entre taxa y entre diferentes unidades ambientales destacan la utilidad de este tipo de analisis en la interpretacion de la variacion espacial de la biodiversidad y deberian contribuir en la planificacion territorial en un marco que optimice la conservacion.