Effect of the lower lip of Monarda didyma on pollen removal by hummingbirds

We examined the effect of the lower lip of Monarda didyma L. on pollen removal by ruby-throated hummingbirds (Archilochus colubris L.) through comparisons of hummingbird visits to natural, lipped flowers versus those that had their lower lip experimentally removed. Birds missed the openings of lipless flowers more often than lipped flowers and thus spent more time attempting to insert their bills into them. Once their bills entered the floral tube, handling times of hummingbirds were significantly longer at lipped than at lipless flowers. Contact durations with anthers and amounts of pollen removed by hummingbirds were significantly greater at lipped than at lipless flowers. Videotapes indicated that lips enhanced pollen removal by slowing a hummingbird's bill insertion into the floral tube, which increased the amount of time that a bird was positioned under a flower's anthers. Unlike the conventional view of hummingbird-flower evolution, which argues for the loss or reduction of lips, our results suggest that lower lips may be maintained in some hummingbird flower species, because they are preadaptations that act as nectar guides for hummingbirds and positioners for optimum pollen removal, in addition to possibly serving as landing platforms or attractants for secondary pollination by bees.