Diet, food preferences, and digestive efficiency of the grayish saltator, a partly folivorous passerine

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 == 54 ±± 26 min) and a relatively low digestive efficiency (average metabolizable energy coefficient == 0.59 ±± 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 == 45 ±± 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.