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The Neotropic Cormorant Nannopterum brasilianus (Gmelin, 1789) is one of the most common and abundant species in Brazil's aquatic environments, but little is known about its natural history. This study elaborates and quantitatively evaluates the ethogram and seasonal abundance of this species at Lake Acu, in Rio de Janeiro, Brazil. Between August 2013 and July 2014, behaviors were registered by the ad libitum sampling method and quantifi ed by the continuous recording during 30-min sessions. The mean number of sighted individuals per month was 30.41 ± 4.79. Abundance was higher during the dry season (41.5 ± 5.36) compared to the rainy season (19.33 ± 4.81) ( t = 3.07, P = 0.01). A total of 42 behaviors were described and grouped into five behavioral categories: maintenance (83.59%), ingestion/excretion (10.67%), locomotion (3.48%), play (1.65%), and agonistic behavior (0.61%). The time spent in these categories did not vary signifi cantly between the morning and afternoon periods. This study can be used as a starting point for further ethological studies on the species.

Although the concept of optimal foraging has been extensively discussed, foraging efficiency is difficult to assess in vertebrates. In this study, we determined the foraging efficiency of the Brazilian cormorant,NannopterumbrasilianusGmelin, 1789, by the direct,ad libitumobservation of a group of four to thirteen individuals in an artificial pond at the University of São Paulo, Piracicaba, state of São Paulo, southeastern Brazil. Although this study was carried out in a highly anthropic environment, we can still conclude that the Brazilian cormorant is a relatively efficient browser and short-term diver. In anthropic environments, foraging success depends on the amount of time these birds spend diving, and stealing food is less common. Stealing occurs at relatively low rates but tends to be an efficient way to get food.