Bird pollination in three species of Phlogacanthus and its broader implications for bird-flower interactions in Asia

Our knowledge of bird-flower interactions in Asia is limited. Here, we investigated the pollination ecology of three Phlogacanthus species that differ substantially in floral tube length. The floral tubes of bird-pollinated flowers may either correspond to the bill length of the primary bird pollinator, or relatively short-tubed flowers may be pollinated by both short- and relatively long-billed birds. The pollination systems of the three Phlogacanthus species may differ in traits other than floral tube length, reflecting their association with different bird groups.

We observed floral visitors at multiple sites over multiple years and compared pollination effectiveness and foraging behavior between bird visitors. We also measured floral traits, including corolla morphology and color and nectar quality and quantity.

The short-, medium-, and long-tubed Phlogacanthus species were mainly or solely pollinated by short-, medium-, and long-billed birds, respectively. The visitor assemblage of the short-flowered species varied considerably with the population in terms of bird species, genus, or family relative to those of the other two Phlogacanthus species. Sunbirds and spiderhunters occasionally hovered to extract nectar. The floral height of the inflorescence determined whether the birds hovered or perched. Although all three Phlogacanthus species are bird-pollinated, they also differ in their nectar and floral morphological traits. These differences likely reflect additional adaptations to distinct bird groups.

The three Phlogacanthus species represent distinct pollination systems connected to the three bird-pollination niches in Asia. Our study provides novel natural historical details associated with bird-flower interactions in Asia.