Comparative Analysis of diet and food-niche relationships in an assemblage of raptors from Mar Chiquita Biosphere Reserve (Buenos Aires Province, Argentina).

BO, MARIA SUSANA, A. MALIZIA, K. SANCHEZ, R. VARGAS, L. BIONDI, M. FAVERO AND A. BALADRÓN.

Termas De Puyehue, Chile

Congreso; . VII Neotropical Ornithological Congress; VII Congreso Chileno de Ornitología.; 2003

Neotropical Ornithological Society y Unión de Ornitologos de Chile

Mar Chiquita Biosphere Reserve (37º40’S, 57º23’W) is an important breeding and  foraging area for diurnal and nocturnal raptors. This area comprises a coastal lagoon, grasslands, marshlands, agricultural fields, woodlands, and dunes. The objective was to evaluate the feeding habits of Polyborus plancus (Pp), Milvago chimango (Mc), Circus buffoni (Cb), Circus cinereus (Cc), Athene cunicularia (Athc), and Asio clamator (Ac) and their trophic relationships during breeding seasons. Between 1993-2002, feeding habits were determinated by the analysis of pellets and prey remains. The contribution made by each prey item to the biomass consumed by raptors, standarized niche breath (Levins’ index) and food-niche overlap index (Pianka’s index), were calculated. In terms of numerical frequency, insects were the most abundant prey item (96-75 %) in the diet of Pb, Mc and Athc, whereas birds, mammals and amphibians were less representative items. In terms of biomass, mammals and birds made the highest contribution to the diet of Pb (75% and 19%, respectively); for Mc it was made by insects (31%), birds (25 %), mammals (23%), and amphibians (17%)., whereas for Athc amphibians contributed with 96% of the biomass. Birds and mammals were the most common prey items (86-43% and 55-13%, respectively) in Cb, Cc, and Ac diet. These same items made the highest contribution to the diet biomass (birds 65-20%, mammals 80-35%). Levins’ index ranged from 0.05 (Mc) to 0.41 (Cb) and Pianka’s index ranged between 0.11% and 64%. These results are discussed in light of trophic interactions among raptors and their different hunting modes, body sizes, diets, and prey availabilities.