High-Speed Video Investigates Mystery of Hummingbird Pollination

Scientists have shot high-speed video of feeding hummingbirds in an effort to understand why the flowers they pollinate almost always hang upside-down.
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Hummingbirds are native to the Americas and are one of the only types of birds that can hover while flying. They expend tremendous amounts of energy as they flit around and have the fastest metabolisms of any animal. Though they also eat small insects, hummingbirds typically drink sugar-rich nectar from flowers to gain precious calories. Many hummingbirds have closely co-evolved with certain plant species but it remains a mystery why the flowers they visit typically hang upside-down.

Because they move so fast, scientists usually watch hummingbird behavior with high-speed cameras, which have in the past revealed exactly how they eat and how they stay dry. In a recent experiment, biologists fed Anna’s hummingbirds (Calypte anna) from artificial flowers that pointed either horizontal, upside-down, or tilted at a 45-degree angle. These fake flowers were filled with nectar and fitted with a mask to measure the amount of oxygen — and therefore energy — the birds used while hovering. The upside-down flowers required the hummingbirds to nod their heads back awkwardly and, surprisingly, required 10 percent more energy to feed from than horizontal flowers.

Because it’s more costly energy-wise to drink from such flowers, the orientation must be beneficial in some other way. The researchers speculate that perhaps flowers that don’t hang upside-down are more exposed to rain, which would dilute the nectar. Hummingbirds can taste the sweetness of the nectar, so they may avoid flowers that contain less sugar.

The findings appear Nov. 21 in Functional Ecology.

Image and videos: Copyright Nir Sapir