Comportamiento de forrajeo del Rayador Sudamericano (Rynchops niger) durante la temporada no reproductiva

MARIANO Y JELICICH, ROCÍO

Puyehue

Congreso; VII Congreso de Ornitología Neotropical; 2003

Sociedad de Ornitología Neotropical

Skimmers are known because of their characteristic bill and particular foraging tactic. Although previous works from North America describe some aspects about the foraging behavior of skimmers, little is known about those aspects during the non-breeding season. In this work I present new information on the foraging ecology of the Black skimmer in estuarine non-breeding areas at Mar Chiquita Reserve (37º40’S, 57º22’W). Information on the diet of skimmers was obtained analyzing regurgitated casts. The structure of fish assemblages was estimated in eight areas used by skimmers to forage. Behavioral observations were carried out to estimate the relative use of different foraging patches, the foraging effort and success. The diet of skimmers was mainly constituted by Silverfish and Anchovies. Some of these species (Odontesthes incisa and Engraulis anchoita) are typical marine, while others (O. argentinensis and Anchoa marinii) are estuarine. Considering the structure of fish assemblages, nine species were found in the area, being Brevoortia aurea, Jenynsia multidentata, O. argentinensis and A. marinii the most important ones. Non significant differences between patches were found in the composition of fish assemblages. However, significant differences were found when fish species found in the diet of skimmers (“fish-prey abundance”) were considered. Significant differences were found in the use of foraging, patches by skimmers, but such differences were not related neither with the abundance nor the diversity of fish assemblages. Considering the areas intensively used by skimmers, we found that: (1) foraging effort increased in areas with higher fish-prey abundance; (2) general fish abundance or fish-prey abundance had no effect on the success rates and (3) tide level had a significant effect on success rates and the number of birds foraging in a patch.