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

Abstract

Mbatha, K., Downs, C.T: & Penning, M. Nectar passage and gut morphology in the Malachite Sunbird and the Black-capped Lory: implications for feeding in nectarivores.Nectar passage and digestive tract morphology of two unrelated nectarivorous bird species, the Malachite Sunbird, Nectarinia famosa, ·and the Block-capped Lory, Lorjus·/or~were examined. X-ray techniques were. used to determine the gross anatomy, and the flow of nectar (an artificial sugar solution) along the gastrointestinal 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 MalachiteSunbir ds. 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 welldeveloped. 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 .Iorys to take larger meals, and hence reduce feeding rate defined as meals/time. Sunbirds on the other hand, must feed frequently.

Diel variations in plasma glucose concentrations of Malachite Sunbirds Nectarinia famosa

“…In contrast, birds that feed less frequently or at long, irregular intervals would have considerable more variation in their plasma glucose concentrations, depending on their feeding rate and the size of their meal (Work 1996;Beuchat and Chong 1998). However, Malachite Sunbirds have no crop for nectar storage (Mbatha and Downs 2002;Downs 2004) and so these birds need to feed frequently during the day to maintain their plasma glucose concentrations and to meet their energy requirements (Downs 2000). Most diurnal birds, like Malachite Sunbirds, feed only during the photophase and then fast during the scotophase.…”

Short‐term energy regulation in nectar‐feeding birds: the response of Whitebellied Sunbirds (Nectarinia talatala) to a midday fast

“…Unlike hummingbirds, sunbirds have no crop or distensible oesophagus for storage (Mbatha, Downs & Penning 2002). Under most conditions, hummingbirds fill their crops to only 10–30% of capacity, but crops enable them to maximize nectar intake during opportunistic feeding by individuals without territories (Carpenter et al .…”

Sugar preferences and digestion by Cape white-eyes,Zosterops virens, fed artificial fruit diets

“…Small birds show no significant difference in overall energy intake between diets of different sugar concentrations (Lloyd 1991;Downs 1997a;Lopez-Calleja & Bozinovic 2003;Markman et al 2006). This may also be a function of gastrointestinal structure, as it has been shown that several small nectarivores lack a crop, and so do not have a storage capacity for ingesta (Mbatha & Downs 2002). By contrast, nectarivorous species with larger crop storing capacities show a less marked sugar preference with change in concentration (Downs 1997b).…”