A small group of specialist birds have figured out how to make a living from sugar water. Nectar-feeding birds drink the sweet liquid that flowers produce to lure pollinators, and in doing so they've pushed avian biology to some of its most extreme limits — the fastest metabolisms, the most precise flight, and beaks shaped like the very flowers they visit. They are, quite literally, birds built by blossoms.
Who drinks nectar?
The nectar-feeding lifestyle has evolved independently on different continents, which makes it a classic case study in convergent evolution — nature arriving at the same answer more than once.
In the Americas, the undisputed masters are the hummingbirds, more than 350 species of them, from the Bee Hummingbird (the smallest bird on Earth) to the sturdy Giant Hummingbird of the Andes. Across Africa and Asia, their ecological counterparts are the sunbirds — similarly tiny, similarly iridescent, and not closely unrelated. In Australia and the Pacific, the honeyeaters and the brush-tongued lorikeets fill the role. Hawaii evolved its own radiation of nectar-sipping honeycreepers. And a long supporting cast — bananaquits, flowerpiercers, some orioles and warblers — takes nectar when available
Look at images of a hummingbird and a sunbird side by side and you're seeing the same job done twice by different toolmakers. A telling difference (other than where you’re observing them): hummingbirds hover in front of a flower on blurring wings, while most sunbirds prefer to perch beside it and lean in.
An engine that runs on sugar
To live on nectar is to live on a knife's edge of energy. Sugar burns fast and clean, and the birds that rely on it have metabolisms unlike anything else with feathers. A hummingbird's heart can beat well over a thousand times a minute, its wings blur at around fifty beats a second, and to fuel all this it must visit hundreds or even thousands of flowers a day, consuming something close to its own body weight in nectar. It lives on the brink of starvation.
One solution to surviving the night — when there are no flowers to visit and no way to feed — is to drop into a state of torpor, letting their body temperature and heart rate plummet into a state close to suspended animation, slashing their energy use until dawn. A bird that runs its engine at full throttle all day simply switches it off to survive until morning.
It was assumed a hummingbird's forked, fringed tongue simply wicked up nectar by capillary action, the way a paper towel soaks up water. Careful high-speed filming revealed something better: the tongue tips spread open inside the nectar and then snap shut as the bird pulls back, actively trapping and pumping the liquid — an elastic micro-trap, not a passive straw.
Beaks shaped by flowers (and flowers shaped by beaks)
Because nectar sits at the bottom of a flower, the shape of a nectar-feeder's bill is a record of the blooms it visits. Straight bills, gently curved bills, and dramatically decurved ones each match a different flower architecture. The Sword-billed Hummingbird carries a ridiculously long beak, the only tool capable of reaching the nectar of certain long, trumpet-shaped passionflowers — and that flower, in turn, can be pollinated by almost nothing else. It’s a highly specialized mutualistic symbiosis – an evolved relationship that benefits both flower and bird.
This is coevolution in action, a slow negotiation running in both directions. Flowers that "want" birds as pollinators have converged on a recognizable style — often red or orange (a color bees see poorly but birds see well), tubular, sturdy, scentless, and filled with copious dilute nectar. Bird-pollinated blooms frequently skip the landing platform that insect flowers provide, since a hovering hummingbird doesn't need one. The plant pays in sugar; the bird pays in pollen ferried from flower to flower. Both are better off, and over millions of years each has sculpted the other.
More than sugar
Nectar is almost pure energy, but it's nearly devoid of protein, so no nectar-feeder can live on it alone. Hummingbirds and sunbirds round out their diet by hawking small insects and plucking spiders — an essential source of the amino acids that sugar can't provide, and the main food they bring to their growing chicks. A hummingbird, for all its floral daintiness, is also a capable predator of gnats and midges.
That reliance on protein is one reason the "hummingbird garden" works best when it isn't sprayed: the same insects a gardener might kill with pesticides are part of what keeps the hummingbirds alive.
Long journeys on tiny wings
It seems impossible that an animal living hours from starvation could migrate, yet many do. The Ruby-throated Hummingbird, weighing about as much as a small coin, fattens up and then crosses the Gulf of Mexico in a single nonstop flight of hundreds of miles over open water. The Rufous Hummingbird makes one of the longest migrations relative to body size of any bird, looping thousands of miles through the Western US as it shuttles between Mexico and Alaska. These journeys are timed to the blooming of flowers along the route — a moving feast the birds must catch at exactly the right moment.
Keepers of the bloom
Ecologically, nectar-feeders are pollinators of enormous importance, especially in the tropics and on islands, where whole plant communities depend on birds to reproduce. Lose the birds and certain flowers set no seed; lose the flowers and the birds starve. It's a tight mutual dependence, and on islands in particular — Hawaii's honeycreepers are the tragic example — the unraveling of these partnerships has driven waves of extinction.
For the rest of us, nectar-feeders are among the easiest wild spectacles to invite home. A garden of native tubular flowers will do more than any feeder, but a clean feeder helps too: dissolve one part plain white sugar in four parts water, skip the red dye entirely, and refresh it every couple of days in warm weather so the nectar doesn't spoil. Do that, and you may find yourself hosting the only birds on Earth that can fly backward — hovering jewels that turned the humble flower into a way of life.