How an Unusual Flower is Pollinated by the Tiny Sunbird: It's All in the Twist

Several unusual flowers in the mountains of western Cameroon possess a nectar spur that curves upwards. This wouldn't be so strange if it weren't for the fact that sunbirds seem to be able to sip from these flowers, despite their unusual shape. Now, scientists have found out how local sunbirds manage to accomplish this feat after recording visitors to a flower continuously over a period of days.

The flower in question is I. frithii, which grows on the surface of smaller trees or lower tree branches. Its red flowers protrude from the foliage and while other flowers are structured so that their pollen falls on birds' bellies or backs, this isn't the case for I. frithii.

When sunbirds insert their beaks into the flower spurs, the flowers actually do a small twist. This small modification significantly affects how pollen is placed on the birds' bodies and actually increases the likelihood that pollen will successfully land on the stigma of another flower, ensuring pollination. It places the pollen on the underside of the birds' heads or bills.

"When we saw the recordings from the cameras, we were really excited," said Michael Bartos, one of the researchers, in a news release. "We did not expect that the fit between flower spur and sunbird bill could be solved in such a simple way. Our enthusiasm was even greater when we realized the adaptive consequence for pollen placement."

The findings reveal not only how birds manage to sip from these flowers, but also how these flowers manage to pollinate other flowers by using the birds.

"Our observations demonstrate that a minute change in floral morphology can effectively overcome constraints resulting from the basal floral architecture early in the group's evolution," write the researchers. "We assume that such adaptations can not only help the plants avoid interspecific competition, but, as the adaptations create strong reproductive barriers, they may also contribute to plant speciation."

The findings are published in the journal Current Biology.