SUGAR PREFERENCES AND SIDE BIAS IN CAPE SUGARBIRDS AND LESSER DOUBLE-COLLARED SUNBIRDS

Using pairwise feeder tests, we studied preferences for sugars in Cape Sugarbirds (Promerops cafer) and Lesser Double-collared Sunbirds (Nec tarinia chalybea). Birds were offered 20% (w:w) solutions of sucrose, fructose, glucose, and a mixture of equal parts of glucose and fructos e. Cafe Sugarbirds showed no preference among these sugars, whereas th e order of preference in Lesser Double-collared Sunbirds was sucrose > fructose = hexose mixture > glucose. Both species showed strong ''sid e biases,'' with individuals consistently drinking more from feeders o ffered on a particular side of the feeder pair. We suggest that this b ias is a manifestation of stereotyped foraging behavior rather than la teralization or true ''handedness.'' The absence of a sucrose aversion in ''fynbos'' (i.e. Cape Floristic Kingdom of southern Africa) nectar ivores such as sugarbirds and sunbirds is not surprising because the f ynbos is characterized by high floral diversity and low bird diversity and by the occurrence of both sucrose-dominant and hexose-dominant ne ctars. However, our findings contradict an earlier generalization that passerines prefer hexoses to sucrose. This generalization is based on studies of several American and European species and of one East Afri can species, and it may be confounded by comparisons of specialized ne ctarivorous nonpasserines with generalized frugivorous/nectarivorous p asserines. In separate feeding trials, both sugarbirds and sunbirds sh owed a strong aversion to the pentose sugar xylose, a nectar sugar new ly described for the Proteaceae. The reason for the occurrence of xylo se in nectar of the Proteaceae is unknown.