Body condition of five passerines in a forest fragment and associated factors

Body condition is a qualitative evaluation of an animal and is directly related to its fitness, with the relative mass index (RMI) as a tool for indirect estimation of energy reserves. This study evaluated if the body condition of birds differs between guilds, if it is reflected in levels of subcutaneous fat, and if it is influenced by the weather season and ectoparasite presence. The RMI was calculated for Antilophia galeata (frugivorous), Arremon flavirostris, Eucometis penicillata (omnivorous), Basileuterus culicivorus, and Myiothlypis leucophrys (insectivorous). It varied among guilds (F2, 295 = 187.92; P < 0.05), with insectivorous species having negative values. The RMI varied between the wet and dry seasons only for A. galeata (F1, 1 = 7.28; P < 0.05) but remained positive throughout the year in omnivorous species. The RMI did not vary with the presence/absence of ectoparasites nor among the different levels of subcutaneous fat, which were predominantly low. The negative RMI of insectivores and its variation in frugivorous between seasons suggest that the body condition is influenced by the type of diet and the availability of food resources, indicating that birds with a specialized diet may be more sensitive to environmental variations that result in fluctuations in the food supply.