Nectar passage and gut morphology in the Malachite Sunbird and the Black-capped Lory: implications for feeding in nectarivores

Abstract

Nectar passage and digestive tract morphology of two unrelated nectarivorous bird species, the Malachite Sunbird, Nectarinia famosa, and the Black-capped Lory, Lorius lory, were examined. X-ray techniques were used to determine the gross anatomy, and the flow of nectar (an artificial sugar solution) along the gastrointes-tinal tract. The Black-capped Lory has a crop while Malachite Sunbirds do not. X-ray analyses showed that labelled meals were briefly stored in the crops of lorys but flowed directly from the oesophagus to the ventriculus in Malachite Sunbirds. Gut morphology of Malachite Sunbirds and a Black-capped Lory were also examined. The sunbirds have a simple gastrointestinal tract anatomy without a crop, whereas the Black-capped Lory has a well-developed crop. We hypothesize that in nectar-feeding birds, the presence of a crop confers foraging flexibility. We predict that the presence of a crop allows lorys to take larger meals, and hence reduce feeding rate defined as meals/time. Sunbirds on the other hand, must feed frequently.