SUGAR PREFERENCES OF A NECTARIVOROUS PASSERINE BIRD, THE LESSER DOUBLE-COLLARED SUNBIRD (NECTARINIA-CHALYBEA)

1. In contrast to hummingbirds, passerine frugivores prefer hexose sug ars to sucrose and absorb sucrose poorly, It has been predicted that t he sugar preferences and digestive physiology of specialized passerine nectarivores will be similar to those of frugivores. 2. We examined t he preferences of 11 Lesser Double-collared Sunbirds, Nectarinia chaly bea (Nectariniidae), for 20% (w/w) solutions of sucrose, glucose, fruc tose, a 1:1 glucose+fructose mixture, and xylose. The order of prefere nce was found to be sucrose=glucose+fructose=fructose>glucose>xylose. The birds rejected xylose, which has recently been found in the nectar of Protea and Faurea (Proteaceae). 3. Preferences for different sugar concentrations were also tested. In the case of sucrose and fructose, the sunbirds preferred 20% to 10% solutions, but were indifferent to 20% vs 30%. They preferred 20% to 30% glucose, but were indifferent to 10% vs 20%. 4. The concentration and sugar composition of the cloacal fluid were measured after feeding on known diets. The sunbirds absorb ed sucrose, glucose and fructose from the ingested food at close to 10 0% efficiency, but xylose was excreted. 5. The results of this study t hus contradict the belief that passerine nectarivores are inefficient at digesting sucrose and reject sucrose in favour of hexose sugars.