Diet diversity and prey selection of Chubut Steamerducks (Tachyeres leucocephalus)

AGÜERO MARÍA LAURA; GARCÍA BORBOROGLU PABLO; ESLER DAN

Cusco

Congreso; IX Congreso de Ornitología Neotropical - VIII Congreso Peruano de Ornitología; 2011

Chubut Steamerduck is a flightless anatid endemic of the Central Patagonia marine coast, Argentina. According to the IUCN Red List of Threatened Species, the species was included under the near threatened category based on the lack of information. The existing information on this species ecology is extremely limited and there is not even precise data about its trophic ecology. Diet diversity and prey selection were analyzed at northern Golfo San Jorge Gulf, Argentina, during the breeding season 2008-2009. A total of 46 faeces were collected along 15 foraging territories. Samples were washed in two sieves (1 and 0.5 mm mesh) under a jet of water. Fragments that were resistant to digestion and diagnostic of invertebrate taxa were identified under a stereoscopic microscope at 10 X 40 magnification. Identification was made to the lowest taxonomic level possible based on preserved material and specific taxonomic keys. Diet diversity was calculated using Levin’s standardized index (Bsta) and prey selection was determined using Jacobs’ index. A total of 13 food items were identified: seven mollusks, two crustaceans, polychaetes and unidentified organic matter. Crustaceans comprised 93.5% of the Steamerducks’ diet, followed by mollusks 69.6% and Nereidiidae 54.35% Taking into account the major food category considered, the Steamerducks’ diet diversity was relatively low (Bsta=0.28). They significantly select Cytograpsus sp. (P<0.001) and Nereidiide (P<0.001), Mollusks and organic matter are all taken in accordance with their abundance. Chubut Steamerducks showed a restricted usage of the available food resources, hence, they could be considered a specialist predator.