Some biologists faced a mystery when they studied a tropical plant called Heliconia tortuosa that has bright red and yellow flowers.
When insects and hummingbirds visit the flowers for their sweet nectar, they carry pollen from other flowers they have visited. The flowers need pollen from another member of their species to reproduce by making seeds. But when scientists hand‑pollinated the flowers the pollination wasn't very effective. So the pollinators must have been doing something that the scientists weren't.
To solve the mystery, the scientists captured specimens of several species of hummingbirds and a species of butterfly that visited the flower. They cleaned the animals of pollen, and let them visit hand‑pollinated Heliconia flowers. The pollination was effective when the flowers were visited by two specific hummingbird species--the violet sabrewing or green hermit.
The two hummingbird species had long curved bills that were a good fit for the flower, but others didn't. Their bills made it possible to drink more nectar than other visitors. So the flowers were choosing their pollinators. When the scientists hand‑pollinated the flowers and then extracted nectar to mimic these hummingbirds, the flowers "turned on" and the pollination worked.
The plant might benefit from its choosiness. For example, if these hummingbird species bring pollen from farther away, the pollen they carry would be more genetically diverse, and produce healthier offspring.
"Some Tropical Plants Pick the Best Hummingbirds to Pollinate Their Flowers" (Science Daily)
"How Tropical Plants Pick the Best Hummingbirds to Pollinate their Flowers" (Science World Report)
"Flowers Choose the Best Pollinators" (Nature)
"Biology of Plants: Pollination" (Missouri Botanical Garden)
"People, Plants, and Pollinators" (National Geographic Live!)