Cecal Fermentation in Mallards in Relation to Diet

A change in tongue volume with body size could be accomplished in several ways.If larger birds had longer tongues, volume could be increased by lengthening.A change in volume could also result from a change in the dimensions of the grooves in tongues of the same length.This appears to be the case for N. verticalis as compared with N. venusta (fig.3), where tongues are the same length but the smaller venusta has a smaller tongue volume.For the larger N. reichenowi, the greater volume is achieved by a slightly longer tongue with much larger grooves (fig.3).Bill length and morphology appear to be well correlated with corolla length and morphology in nectarfeeding birds (Snow and Snow 1972, Wolf et al. unpubl.data).This co-evolutionary relationship presumably provides for ease in reaching and extracting nectar at the base of differently shaped flowers.Bill morphology among hummingbirds and sunbirds is so diverse that birds of similar sizes may have different bill lengths.If tongue morphology reflects such differences, birds of similar sizes could have different tongue volumes.It would be of interest to determine the extent to which this may relate to rates and efficiencies of nectar intake for such species visiting flowers with which they have co-evolved. SUMMARYThe structure and function of sunbird tongues were compared with those of hummingbirds.In experiments with Nectarinia kilimensis, the rate of nectar intake from a feeder decreased with increasing "corolla" length, primarily as a result of less nectar obtained per lick.The grooves on the tongues of sunbirds vary in volume with body size such that the tongues of larger sunbirds could hold more nectar.However, the tongues of sunbirds appear to hold less nectar than those of smaller species of hummingbirds.Thus, hummingbirds, which expend more energy while hovering to consume nectar, may obtain more nectar/lick, but sunbirds' less costly method of perching while feeding should make their nectar extraction CECAL FERMENTATION IN MAL-LARDS IN RELATION TO DIET