Fruit use and fruit processing by euphonias, specialized avian frugivores

Abstract

Euphonias (Neotropical passerines in the genera Euphonia and Chlorophonia) form the quintessential example of a specialized avian frugivore, combining a high reliance on fruit as food and the restriction of fruit taxa exploited. To understand their specialization, we explored the integration of fruit morphological and nutritional traits with their internal processing by euphonias. We made a literature survey of the fruits eaten by euphonias, and compared their digestive morphology (intestine length and internal surface area) and the traits of the fruits they eat (fruit and seed diameters, number of seeds, water, lipids, protein and sugar contents) with other frugivorous bird species. Although eating a variety of fruit species, euphonias concentrate feeding on a few plant families and genera (Miconia, Ficus, Cecropia, Phoradendron, Rhipsalis), favoring watery, lipid-poor, often sugar-rich fruits with small seeds. They also have longer intestines than the other frugivorous birds, which may contribute to the efficient absorption of nutrients despite their necessity to rapidly pass fruits through the gut. We argue that the specialization of euphonias that make them to rely heavily on particular plant taxa is largely mediated by their fruit processing constraints that limit the functional traits of the fruits exploited. Our results show that birds with most of their diets composed of fruits should not necessarily consume fruits of a wider variety of plant species. It also reinforces the importance of considering the matching between fruit morphology and the internal processing of fruits to understand fruit use by birds.