Cuban, D.; Wang-Claypool, C.; Dalimunthe, Y.; Downs, C. T.; Bowie, R. C. K.; Brau, F.; Johnson, S.; Rico-Guevara, A.

Nectarivory has independently evolved about 30 times within birds, yet little is known about the nectar-feeding mechanisms used by these very different types of birds. Multiple groups have relatively long bills and tube-like tongues hypothesized to be adaptations for nectar extraction. Sunbirds are the group that exhibits the largest bill and tongue convergence with the well-studied hummingbirds. Using microCT scans we characterize the details of the sunbird feeding apparatus and using high-speed video experiments we describe their nectar-feeding mechanism. Sunbirds collect nectar through their bi-cylindrical tongues reciprocating them around 9 times per second. Multiple lines of kinematic evidence and further fluid dynamics modeling indicate that sunbirds use a unique drinking mechanism not found in any other bird: suction feeding through the tongue. These findings are consistent across a wide sampling of sunbird species from the geographical extremes of their range, implying that these mechanics are shared by the entire Nectariniidae family. Our findings describe a heretofore undescribed feeding mechanism in vertebrates, suction through the inside of the tongue, and sets the stage for investigating the physical limitations imposed by flowers and fluid dynamical effects of different nectar types in the flowers that sunbirds visit in nature.