DIET, FOOD PREFERENCES, AND DIGESTIVE EFFICIENCY OF THE GRAYISH SALTATOR, A PARTLY FOLIVOROUS PASSERINE ADRIANA RODRI ´ GUEZ-FERRARO 1 , M. ALEXANDRA GARCI ´ A-AMADO 2 , AND CARLOS BOSQUE Laboratorio de Biologı ´a de Aves, Depto. de Biologı ´a de Organismos, Universidad Simo ´n Bolı ´var, Apartado 89.000, Caracas 1080-A, Venezuela Abstract. We studied the diet of the Grayish Saltator (Saltator coerulescens) during the rainy and dry seasons in the Venezuelan llanos and examined its food preferences, digesta retention time, rate of food intake, and digestive efficiency, in captivity. Grayish Saltators fed almost exclusively on plant tissues throughout the year. Fruits and leaves were the most commonly consumed items, comprising 36% and 28% of the diet, respectively, averaged over the entire year. In pairwise choice trials, saltators preferred fruits over leaves and flowers, and wild over cultivated leaves. In the laboratory, saltators displayed food- processing traits typical of frugivorous passerines. When feeding on a fruit (banana mash) diet, they had a fast rate of food passage (digesta mean retention time 5 54 6 26 min) and a relatively low digestive efficiency (average metabolizable energy coefficient 5 0.59 6 0.11), which was compensated for by high rates of food intake (1.4 times body mass). Mean retention time of a leaf-supplemented diet was slightly shorter (average 5 45 6 17 min). Birds maintained or increased their body masses under laboratory conditions when fed on a fruit diet but did not when fed exclusively with leaves. Saltators spent very little time foraging, and the amount of time varied seasonally (5% and 17% of the time in the rainy and dry seasons, respectively). Most of their time (ca. 50%) was dedicated to resting. The morphology of the digestive tract of this species is similar to other frugivorous birds, but the inner edge of the maxilla is serrated. We found no evidence of cellulolytic activity in the Grayish Saltator’s gut. Together, all of these characteristics indicate that Grayish Saltators are partial folivores that rely on a ‘‘skimming’’ strategy of food consumption. Key words: assimilation efficiency, digestion, folivory, frugivory, Grayish Saltator, Saltator coerulescens, time budget. Dieta, Preferencia Alimenticia, y Eficiencia Digestiva de Saltator coerulescens, un Passeriforme Parcialmente Folı ´voro Resumen. Estudiamos la dieta de Saltator coerulescens durante las estaciones de lluvia y sequı ´a en los llanos de Venezuela y examinamos sus preferencias alimenticias, el tiempo de retencio ´ n del alimento, la tasa de ingesta del alimento y la eficiencia digestiva en cautiverio. Los S. coerulescens se alimentaron exclusivamente de tejidos vegetales a trave ´s del an ˜ o. Las frutas y hojas fueron los ı ´tems consumidos ma ´ s comu ´ nmente, comprendiendo un 36% y 28% de la dieta, respectivamente, promediado en todo el an ˜ o. En pruebas de preferencia pareadas, los S. coerulescens prefirieron frutas sobre hojas y flores, y hojas silvestres sobre cultivadas. En el laboratorio, los S. coerulescens mostraron caracterı ´sticas para el procesamiento del alimento tı ´picas de passeriformes frugı ´voros. Cuando se alimentaron con una dieta de fruta (pasta de banana) mostraron una ra ´ pida tasa de pasaje del alimento (tiempo de retencio ´ n promedio del alimento 5 54 6 26 min) y una relativamente baja eficiencia digestiva (coeficiente de energı ´a metabolizable promedio 5 0.59 6 0.11), la cual fue compensada con altas tasas de ingesta de alimento (1.4 veces la masa corporal). El tiempo de retencio ´ n promedio de una dieta suplementada con hojas fue ligeramente ma ´ s corto (promedio 5 45 6 17 min). En condiciones de laboratorio, las aves mantuvieron o aumentaron su masa corporal cuando fueron alimentados con una dieta de fruta pero no lo hicieron cuando se alimentaron exclusivamente con hojas. Los S. coerulescens pasaron muy poco tiempo alimenta ´ ndose, y dicha cantidad de tiempo vario ´ Manuscript received 1 March 2007; accepted 28 August 2007. 1 Present address: Department of Biology, Research Building 223, University of Missouri-St. Louis, One University Blvd., St. Louis, MO 63121-4499. E-mail: arppf@umsl.edu 2 Present address: Laboratorio de Fisiologı ´a Gastrointestinal, Centro de Biofı ´sica y Bioquı ´mica, Instituto Venezolano de Investigaciones Cientı ´ficas, Km 11 Carretera Panamericana, Miranda 1020, Venezuela The Condor 109:824–840 # The Cooper Ornithological Society 2007 [824] Downloaded from https://academic.oup.com/condor/article/109/4/824/5563663 by guest on 30 June 2023