Sources of Assimilated Protein in a Specialized Tropical Frugivorous Bird, the Yellow-throated Euphonia (Euphonia hirundinacea)

Abstract

Most frugivorous birds must complement their diet with insects to fulfill their protein requirements; species that rely almost exclusively on fruits are rare. We used nitrogen ( 15 N: 14 N) stable-isotope analysis of whole blood to quantify and compare the use of insects and fruits as sources of assimilated nitrogen in a specialized frugivorous bird, the Yellow-throated Euphonia (Euphonia hirundinacea). Nitrogen stable-isotope analysis is particularly useful for examining the relative contribution of animal and plant products as sources of assimilated nitrogen, because there is trophic enrichment of the heavier isotope in higher trophic levels of food webs. We found that most assimilated nitrogen was derived from fruits (76-100%), with a slight increase in the contribution of fruits as their abundance increased. In comparisons of bird species, δ 15 N values of Yellow-throated Euphonia were lower than those of insectivorous and piscivorous species but similar to the values found in seed-fruit eaters. Our results suggest that the dependence on fruits as a source of assimilated nitrogen in Yellow-throated Euphonia ranged from predominant to almost exclusive during the period of our study (February-August). Total dependence on fruits as a source of assimilated nitrogen is not a common phenomenon among birds, but it may be favored in the tropics, where fruits are more abundant and diverse. Fuentes de Proteína Asimilada en Euphonia hirundinacea, un Frugívoro EspecialistaResumen.-La mayoría de las aves frugívoras deben complementar su dieta con insectos para satisfacer sus requerimientos de proteína, por lo que son pocas las especies que se alimentan solamente de frutos. En este estudio, se realizó un análisis de isótopos de nitrógeno ( 15 N: 14 N) de la sangre de Euphonia hirundinacea para cuantificar el uso de insectos y frutos como fuentes de nitrógeno asimilado. Esta especie de ave es especialista en el consumo de frutos del muérdago. El análisis de isótopos de nitrógeno es empleado para examinar la contribución de fuentes animales y vegetales de nitrógeno asimilado, gracias a que existe un enriquecimiento trófico del isótopo más pesado en niveles más altos de la red trófica. Se encontró que la mayor parte del nitrógeno asimilado provenía de los frutos (76-100%), con un pequeño incremento en la contribución de los frutos a medida que su abundancia aumentó. Cuando se comparó con otras especies de aves, los valores de δ 15 N de E. hirundinacea fueron similares a los de las especies granívoras o frugívoras, pero menores que los de las especies insectívoras y piscívoras. Nuestros resultados sugieren que los frutos fueron la fuente primordial de nitrógeno asimilado para E. hirundinacea durante el tiempo del estudio (febrero-agosto). Este fenómeno no es común en la mayoría de las aves, pero podría verse favorecido en el trópico húmedo donde las plantas con frutos son más diversas y abundantes.

Stable isotopes identify dietary changes associated with beak deformities in Black-capped Chickadees (Poecile atricapillus)

“…First, chickadees specialize during the winter on lipid-rich foods, such as suet, and lipid extraction of such foods would have essentially removed them from analysis. Second, carbon from dietary lipid has been shown to make major contributions to tissue proteins in passerines, particularly when they are fed high-fat and low-protein diets similar to those of wintering chickadees McWilliams 2006,2007;Herrera M. et al 2009). …”

Why do some, but not all, tropical birds migrate? A comparative study of diet breadth and fruit preference

“…Sampling broadly from the fruits available may thus be necessary in order to complete the nutritional needs of an obligate frugivore. In at least a few species of frugivores, fruits apparently fill the total protein requirements of individuals (Bosque and Pacheco 2000;Herrera et al 2009). Yet dietary choices can be influenced by small changes in protein levels, supporting the idea that fruit choices result from an interaction between the endogenous state of an individual and the morphological and chemical traits of fruits (Bosque and Calchi 2003;Schaefer et al 2003).…”

The significance of unripe seeds and animal tissues in the protein nutrition of herbivores

“…Tropical hummingbirds, Australian lorikeets and honeyeaters all eat insects and especially feed them to their nestlings (White, 1993 Section 7.2; Oliver, 1998; Oliver et al , 2003). Few if any frugivorous birds, and especially their young, could get adequate protein without eating insects (Herrera, Rodriguez & Hernandez, 2009).…”