Birds
Hummingbird
Trochilidae · also called hummingbirds
A hummingbird is a bird pushed to the edge of what a warm-blooded animal can do. It is the smallest bird there is, it can hang motionless in the air and fly backwards, its heart beats over a thousand times a minute, and it runs so hot that most nights it has to partly switch itself off just to reach morning alive.
Overview
Hummingbirds are the family Trochilidae, around 360 species, found only in the Americas and most diverse in the tropical Andes. They range from the 2 g bee hummingbird, the smallest bird in the world, to the 20 g giant hummingbird. All feed mainly on flower nectar, taken through a long tube-like tongue, and all can hover.
Hovering flight
A hummingbird’s wing is nearly rigid and pivots at the shoulder, flipping over on the backstroke so it makes lift on both the forward and backward sweep. The wingtips trace a figure-eight, and tilting that figure lets the bird hang still, rise vertically, or fly backwards — something no other bird can do. The cost is huge, so hummingbirds perch most of the day.
A metabolism at the limit
In flight the heart can pass 1,200 beats a minute and the bird takes ~250 breaths a minute. It stores only a few hours of fuel, so on cold nights it drops into torpor, letting its body temperature fall toward the air and its heart rate to ~50, cutting energy use by up to 95 per cent until dawn.
Nectar is not enough
Nectar is pure sugar, so hummingbirds also hunt small insects and spiders for protein and fat, and feed their nestlings almost entirely on that. Some species perform extraordinary journeys — the ruby-throated hummingbird crosses 800 km of the Gulf of Mexico non-stop.
Status
Hummingbirds as a family are Not Evaluated. Many are common and take well to garden feeders, but around 10 per cent are threatened, mostly Andean and Caribbean species tied to single cloud forests or islands, such as the marvellous spatuletail.
Hummingbird: common questions
How do hummingbirds hover?
They flap in a way no other bird can. A hummingbird's wing is nearly rigid from the wrist out and pivots almost entirely at the shoulder, which can rotate the whole wing through about 180 degrees. On the backstroke the wing flips over so its leading edge still cuts forward through the air, so the bird produces lift on both halves of the stroke instead of only the downstroke. The wingtips trace a horizontal figure-eight, and by tilting the plane of that figure-eight the bird pushes air down to hover, back to retreat, or up to climb vertically. The trade-off is that this is extremely expensive, which is why hummingbirds spend most of the day perched.
Why do hummingbirds go into torpor at night?
Because their fuel tank is tiny relative to how fast they burn through it. A hummingbird's high body temperature and racing metabolism mean it can starve within a couple of hours if it stops feeding, and it cannot feed in the dark. To bridge the night, especially a cold one, it lets its body temperature fall close to the surrounding air, sometimes from around 40 degrees Celsius down to 10 or lower, and slows its heart from over a thousand beats a minute to perhaps 50. In this torpid state it uses as little as 5 per cent of its normal energy. At dawn it shivers and warms back up over 20 minutes to an hour before flying off to feed.
What do hummingbirds eat besides nectar?
Small arthropods, and they need them. Nectar is almost pure sugar and water, which fuels flight but contains no protein, fat, vitamins, or minerals, so a hummingbird cannot build muscle, produce eggs, or feed nestlings on nectar alone. Hummingbirds hawk tiny flying insects such as gnats and midges out of the air, glean aphids and spiders from leaves, and steal trapped insects and even silk from spider webs. Nestlings are fed almost entirely on this insect matter, regurgitated by the female. A hummingbird may eat hundreds of small insects a day alongside its nectar rounds.
Are hummingbirds attracted only to red flowers?
They favour red and orange, but they are not limited to them. Hummingbirds see colour well, including some ultraviolet, and many bird-pollinated flowers in the Americas are red or orange with a long tubular shape, little scent, and a dilute nectar, a syndrome that suits hummingbird vision and bills while being less obvious to bees. But hummingbirds readily visit purple, pink, yellow, and even white flowers if the nectar reward is good, and they quickly learn which individual plants and feeders are productive regardless of colour. Bright red is a useful cue for a garden feeder, but coloured water or dye is unnecessary and best avoided.