A classification scheme for avian diet types

Descriptions of avian diets currently lack consistent terminology and standardized methods. As a consequence, most available classifications, especially for tropical birds, are inconsistent and often misleading. We identified 23 food categories most commonly eaten by birds (e.g., seeds, fruits, and insects) and proposed standard names that accurately describe the diet type associated with each food category (e.g., granivore, frugivore, and insectivore). We also propose a classification scheme for avian diet types that takes into account the number of food categories consumed and the volumetric proportion (based on stomach content analysis) of each category eaten to indicate the diet type of a species, using a binomial terminology. Given that bird diets encompass a continuum between some extremes commonly treated as distinct categories, we adopted arbitrary breaking points to delimit distinct diet types. For example, species with different proportions of insects and fruits in their diets can be classified as insectivores (IN), insectivores secondarily frugivores (INFR), frugivores-insectivores (FR-IN), frugivore secondarily insectivores (FRIN), and frugivores (FR). Because many factors can influence avian diets, the diet types of species can also be classified based on age-related, sexual, seasonal, and/or geographic variation, e.g., young are insectivores and adults are frugivores, we believe that our classification scheme provides a standardized terminology that can contribute to a more consistent and effective exchange of information about avian diets.