Guillermo E. Soave

The importance of fish in the diet of the South Polar Skua (Stercorarius maccormicki) at the South Shetland Islands, Antarctica

Abstract Where South Polar Skuas (Stercorarius maccormicki) occur in the absence of Brown Skua (S. antarcticus), their main prey consists of other birds. In contrast, where the two species occur together, fish appears to dominate the diet of South Polar Skuas, probably because Brown Skuas monopolise the terrestrial resources. Twenty-eight stomach samples of South Polar Skuas were collected throughout the breeding season at Half Moon Island, South Shetland Islands, Antarctica. Fish were the most dominant prey item (100% frequency, 98% prey mass); their importance remained constant throughout the study period. Although there is a colony of Chinstrap Penguin (Pygoscelis antarctica) nearby the South Polar Skua population and there are very few Brown Skuas, the South Polar Skuas did not eat penguins. The result suggests fish are selected preferentially over terrestrial resources, at least in certain regions, and particularly when availability of terrestrial resources is limited. Thus, competitive exclusion by Brown Skuas may not fully explain dietary choice of South Polar Skuas.

Seeds in the Diet of the White-rumped Sandpiper in Argentina

Abstract The White-rumped Sandpiper (Calidris fuscicollis) breeds in Alaska and Canada, and during the nonbreeding season migrates to South America. The reported diet of this sandpiper is principally invertebrates; seeds are a very rare item. This species was studied at Guamini Pond, Buenos Aires Province, Argentina, in December 1997. The stomach contents of 23 adults were investigated. The analysis showed that during the sampling period the only food eaten by the White-rumped Sandpiper were seeds. Them were represented by the following families: Caryophylaceae, Chenopodiaceae, Fabaceae, Malvaceae, Polygonaceae, Ulmaceae, Cyperaceae and Poaceae. The seeds ranged between 0.83 and 2.25 mm in length. Stones and fragments of algae were found in all samples, the algae possibly ingested accidentally during feeding. Our findings indicate that the White-rumped Sandpiper forages on different items depending on the area, season and availability, and may be an opportunistic feeder.—The White-rumped Sandpiper ( Calidris fuscicollis ) breeds in Alaska and Canada, and during the nonbreeding season migrates to South America. The reported diet of this sandpiper is principally invertebrates; seeds are a very rare item. This species was studied at Guaminí Pond, Buenos Aires Province, Argentina, in December 1997. The stomach contents of 23 adults were investigated. The analysis showed that during the sampling period the only food eaten by the White-rumped Sandpiper were seeds. Them were represented by the following families: Caryophylaceae, Chenopodiaceae, Fabaceae, Malvaceae, Polygonaceae, Ulmaceae, Cyperaceae and Poaceae. The seeds ranged between 0.83 and 2.25 mm in length. Stones and fragments of algae were found in all samples, the algae possibly ingested accidentally during feeding. Our findings indicate that the White-rumped Sandpiper forages on different items depending on the area, season and availability, and may be an opportunistic feeder. Received 25 October 2002, accepted 29 December 2002.

White-faced Ibis Diet in Argentina

Abstract Seasonal composition and sexual differences in the diet of the White-faced Ibis (Plegadis chihi) were investigated in Buenos Aires Province, Argentina. A total of 88 stomach contents were analyzed, from White-faced Ibis feeding on riparian pastures and grasslands in the Magdalena district, Buenos Aires Province, Argentina. Samples were obtained between 1992 and 1996, covering each season of the year. The trophic spectrum was determined based on the identification of 59 items, mainly belonging to animal taxa. Diet was composed of Insecta (43 items), Arachnida (3 items), Crustacea (5 items), Gastropoda (3 items), Hirudinea (3 items), Amphibia (1 item) and vegetable (1 item). Dietary composition was analyzed in terms of number, frequency of occurrence and volume, for each season and between sexes. Significant differences between sexes were found in the volume of the ingestion consumed.

Winter diet of Great Pampa-finches Embernagra platensis in Guaminí Lagoon, Argentina

Abstract. The diet of the Great Pampa-finch includes seeds rather than insects. Our objective was to study its diet during the winter season and, whenever possible, to record differences between the sexes in diet patterns. This species was studied at Guamini Lagoon, Buenos Aires Province, Argentina. The stomach content of 38 adult birds was investigated. The analysis shows that the food eaten by E. platensis consisted of seeds (60%) (Chenopodiaceae, Asteraceae, Ciperaceae and Poaceae) and insects (39%) (Bellostomatidae, Dytiscidae, Curculionidae, Coccinelidae, Formicidae and Apidae). Males ate more insects and, overall, more items than females. These, in turn, consumed a greater amount of plants. Niche breadth values were 2.9 for males and 3.1 for females. The seeds encountered were those of plant species typically associated with the pampas.

Diet of Cape Petrel Daption capense Chicks on South Shetland Islands, Antarctica

Abstract. The diet of the Cape Petrel was investigated in two localities of South Shetland Islands, Antarctica, over the period January—February 1996. Stomach contents of adults obtained by flushing and regurgitates of chicks were sampled during the chick-rearing period. During the whole sampling period, euphausiids represented the predominant prey in terms of frequency of occurrence, mass and number at Fildes Peninsula, while at Harmony Point, euphausiids and fish components were found in similar proportions in terms of mass and frequency. Myctophiids fish, in particular Electrona antarctica, formed the bulk of the fish component. The analysis of the diet throughout the breeding season showed significant differences in number and mass of the prey items at Fildes Peninsula, while at Harmony Point, there were significant differences also in the occurrence of preys. Considering both localities, although the occurrence of the prey did not vary significantly during the brooding period, there were significant differences in their number and mass. Similar results were found in the post-brooding period between both localities.