Diet of Black-crowned Night-herons (Nycticorax nycticorax) in a Wetland of the Parana River´s Alluvial Valley

Abstract

We analysed the feeding ecology of Nycticorax nycticorax based on fourty individuals captured on the Carabajal Island (Santa Fe, 31o39’S, 60o42’W), determining the minimum sample, index of relative importance (IRI), size of prey, feeding efficiency, dietary selectivity, amplitude of the trophic niche, circadian rhythm of feeding activity, and habitat preference. The trophic spectrum was made up of 16 taxonomic entities, mainly fishes (IRI= 9.100), followed by insects (IRI= 1.650), and crustaceans (IRI= 600). The highest percentage of prey size was found in the range of 61-80 mm. The amplitude of the trophic niche ranged between 2.55 and 5.22, and the feeding efficiency between 92.3% and 99%. In relation to dietary selectivity, the correlation between abundance of prey in stomachs and abundance of prey in the study area yielded significant results (r = 0.41, P > 0.001). The rhythm of feeding activity showed high activity very early in the morning, decreasing towards noon, and increasing again at dusk. Grasslands and Aquatic vegetation were units of vegetation and environment selected more frequently.