On the feeding biomechanics of nectarivorous birds

Nectar-feeding birds employ unique mechanisms to collect minute liquid rewards hidden within floral structures. In recent years, techniques developed to study drinking mechanisms in hummingbirds have prepared the groundwork for investigating nectar feeding across birds. In most avian nectarivores, fluid intake mechanisms are understudied or simply unknown beyond hypotheses based on their morphological traits, such as their tongues, which are semi-tubular in sunbirds, frayed-tipped in honeyeaters and brush-tipped in lorikeets. Here, we use hummingbirds as a case study to identify and describe the proposed drinking mechanisms to examine the role of those peculiar traits, which will help to disentangle nectar-drinking hypotheses for other groups. We divide nectar drinking into three stages: (1) liquid collection, (2) offloading of aliquots into the mouth and (3) intraoral transport to where the fluid can be swallowed. Investigating the entire drinking process is crucial to fully understand how avian nectarivores feed; nectar-feeding not only involves the collection of nectar with the tongue, but also includes the mechanisms necessary to transfer and move the liquid through the bill and into the throat. We highlight the potential for modern technologies in comparative anatomy [such as microcomputed tomography (μCT) scanning] and biomechanics (such as tracking BaSO4-stained nectar via high-speed fluoroscopy) to elucidate how disparate clades have solved this biophysical puzzle through parallel, convergent or alternative solutions.