Hummingbird anatomy is built around a single move that no other vertebrate can sustain: hovering in still air for as long as the bird wants to stay there. The hummingbird (around 360 species in the family Trochilidae, all of them in the Americas) does this with a wing that rotates almost 180 degrees at the shoulder and generates lift on both halves of the beat, a chest filled by flight muscles that account for 25 to 30 percent of body mass, a heart that beats up to 1,260 times a minute in active flight, and a forked tongue that pumps nectar into the throat 15 times a second.
The body runs on sugar at around ten times the per-gram metabolic rate of a human running, and the supply runs out every night, which is why most species drop into torpor at sunset and lose half their body temperature to survive until morning. Sizes range from the 6 cm 2 g bee hummingbird (Mellisuga helenae) of Cuba, the smallest bird alive, to the 22 cm 24 g giant hummingbird (Patagona gigas) of the Andes, but every species shares the same shoulder-rotating wing, oversized chest, pump-action tongue, and torpor-capable physiology that has dominated American flowers for around 22 million years.
Hummingbirds belong to the order Apodiformes (“the legless ones”), a group they share with the swifts and the tree-swifts. The shared name reflects the small, weak feet that are usable only for perching: a hummingbird cannot walk, hop, or run, and to move from one twig to another a few centimetres away the bird flies. The order’s three families share an enlarged shoulder joint, short upper arm bones, long hand and finger bones, and a wing built to generate lift on the upstroke as well as the downstroke.
Hummingbirds have pushed every one of those features to the extreme: the shoulder rotates further, the flight muscles are larger, the heart is faster, and the metabolism runs hotter than in any other bird. The shared body plan covered on this page applies across the family, from the bee hummingbird to the swordbill to the giant hummingbird; for the species list, see Hummingbird Species: A List of All 361 Hummingbird Types.
The Wing: Figure-of-Eight Beat and the Rotating Shoulder
A hummingbird wing does not flap up and down in the way every other bird’s wing does. The wing sweeps forward and backward, almost level with the bird’s body, and on each sweep the leading edge twists through almost 180 degrees at the shoulder, so that the underside of the wing on the forward stroke becomes the upper side on the backward stroke. The wingtip traces a flat figure of eight in the air, and lift comes from both halves of the beat: the forward stroke pushes air down and back, and the backward stroke pushes air down and forward.
Most birds get their lift from the downstroke and recover passively on the upstroke; the hummingbird gets lift on both. The shoulder joint that allows the rotation is unique to hummingbirds and to their closest relatives, the swifts, and the bones of the wing have shifted in proportion to support it: the upper arm (humerus) is short and stout, the radius and ulna are short, and the hand and finger bones are long, with the wing acting as a single rigid blade pivoting at the shoulder rather than bending at the elbow.
The muscle that powers the downstroke is the pectoralis, which in a typical bird accounts for around 15 percent of body mass and in a hummingbird climbs to 25 to 30 percent, the largest in any bird relative to its body. The muscle that powers the upstroke is the supracoracoideus, which in most birds is around half the mass of the pectoralis and in a hummingbird is more than half, because the upstroke is doing an equal share of the lift work.
Together the two flight muscles fill the entire chest cavity and account for around a third of the bird’s total mass, leaving the rest of the body to be packed in around them. Wingbeat frequency runs from 50 to 80 beats per second in normal hovering across most species (the smaller the bird, the faster the beat), and climbs to over 200 beats per second during the courtship dive of a male Anna’s hummingbird, when the air rushing past the outermost tail feather makes the high-pitched squeak that is the only sound a hummingbird produces with its body rather than its voice.
The Heart: 1,260 Beats per Minute and a Two-Hour Day Off
The cost of flight on this scale is paid by the cardiovascular system. A resting hummingbird’s heart beats around 250 times per minute (against 60 to 80 in a resting human), and during active flight the rate climbs to between 1,000 and 1,260 beats per minute depending on species and effort, with the blue-throated mountaingem (Lampornis clemenciae) of Mexico holding the record at 1,260. A heart at this rate is too fast for the human ear to count and runs as a single tone.
The heart itself is large in proportion to body mass at around 2.5 percent (against 0.5 percent in a human), and the blood carries a haemoglobin variant tuned to load oxygen at the high altitudes some hummingbird species reach: the giant hummingbird feeds at 4,000 m in the Andes, and the Andean hillstar (Oreotrochilus estella) breeds at 5,200 m on the slopes of Chimborazo, higher than any other small bird.
The lungs are small in absolute terms but operate the same one-way airflow system used by every bird (nine air sacs that draw fresh air through a pair of rigid lungs in a single direction on both inhalation and exhalation), which extracts around 30 to 40 percent more oxygen per breath than a mammalian lung can manage. Even with this efficient lung, the bird’s metabolic demand is enormous: a hummingbird in flight burns through energy at around 10 times the per-gram metabolic rate of a human running, around 50 times the rate of a small mammal of comparable size, and around 100 times the rate at which the bird itself burns sugar at rest. The bird must eat its own body weight in nectar every day to keep up, and it does so by visiting hundreds of flowers between sunrise and sunset.
The Tongue: A Forked Pump That Cycles 15 Times a Second
A hummingbird visits hundreds of flowers in a day, hovers for a few seconds at each, inserts its long thin beak into the corolla, and extends its tongue past the tip of the beak into the nectar reservoir. The tongue is split for around half its length into two grooved branches, with thin elastic flaps along the edges of each groove, and the way it moves nectar into the throat was misunderstood for the better part of two centuries.
The classical explanation, going back to Martin Lister in the 17th century, was capillary action: nectar would climb the tongue grooves the way water climbs a thin tube. High-speed video published by Alejandro Rico-Guevara and Margaret Rubega in 2011 (and refined by the same researchers since) showed this is wrong. The tongue is not a wick; it is a pump.
As the tongue dives into the nectar, the pressure of the surrounding fluid forces the elastic flaps open, and the grooves fill from the sides. As the tongue is withdrawn back into the beak, the flaps roll closed, trapping nectar inside the grooves, and the beak compresses the tongue from above and below to squeeze the trapped nectar into the throat. The tongue cycles in and out of the beak around 15 times a second, and each cycle delivers a small but measurable volume of sugar water to the digestive tract.
The beak itself is shaped to the flowers each species feeds on: the ruby-throated hummingbird’s beak is short and straight, the swordbill (Ensifera ensifera) of the Andes carries a beak longer than its own body and rests with the head tilted upward because the head muscles cannot support the beak’s weight horizontally, and the white-tipped sicklebill (Eutoxeres aquila) of Central and South America carries a beak that curves like a fishhook to fit the curved corollas of Heliconia flowers. Each beak shape has co-evolved with a specific group of flowers, and many flowers depend on a single hummingbird species to carry their pollen.
Eyes, Tetrachromatic Vision and the Ultraviolet Channel
A hummingbird’s eyes are large in relation to its head, set on the sides for a near-panoramic field of view, and built to see colour with one more channel than the human eye uses. Where the human retina carries three cone photoreceptor types (red, green, blue), the hummingbird retina carries four: the fourth is sensitive to ultraviolet light at wavelengths between 300 and 400 nm, below the threshold of human vision. Many of the flowers a hummingbird feeds on carry UV patterns invisible to people that act as landing strips, and the bird perceives a “non-spectral” colour space (combinations of UV with red, green, or blue) that no human can experience.
To a hummingbird, a red flower against green foliage is even more conspicuous than it appears to a human, which is why the red plastic of garden hummingbird feeders works as a visual lure: red contrasts strongly against vegetation in a tetrachromatic eye, even though the bird does not preferentially seek red over other colours when foraging in the wild.
The Skeleton: Pneumatic Bones, Fused Vertebrae, Tiny Feet
The hummingbird skeleton is built on the same lightweight, hollow-boned plan as in every other flying bird, with the long bones, parts of the skull, the sternum, and parts of the vertebral column pneumatic (air-filled and connected to the air sac system) and reinforced internally by trabecular cross-struts. The keeled sternum is large in proportion to the body and provides the anchor for the oversized pectoralis and supracoracoideus muscles, with the supracoracoideus running through a pulley-like opening in the shoulder so it can pull from below while lifting the wing from above (the same arrangement used in all flying birds, but with both muscles enlarged in the hummingbird).
The cervical vertebrae are reduced in number compared with most birds and the neck is short, which keeps the head close to the centre of mass during the high-frequency wingbeat. The hindlimbs are reduced to the minimum that will support a perching grip: the femur is short, the tibiotarsus and tarsometatarsus are slender, and the four toes (three forward, one back, the standard bird arrangement) are small and weak.
A passive tendon-lock at the ankle holds the toes flexed around a perch without active muscle work, the same mechanism used by perching songbirds and by raptors, scaled down to a body that fits on the head of a child’s pencil.
Torpor: Switching Off for the Night
A bird that burns sugar at the rate a hummingbird burns it cannot survive a cold night without a metabolic shutdown. Even a small adult hummingbird with a full crop of nectar at sunset would burn through its fat reserves before sunrise at normal body temperature in cool conditions, and so most species drop into torpor (a controlled, reversible state of profound metabolic depression) at the end of the day.
The body temperature falls from a daytime 38 to 40 degrees Celsius to as low as 12 to 18 degrees, the heart rate falls from 250 beats per minute at rest to between 50 and 180 depending on species and ambient temperature, the breathing rate slows from around 250 breaths per minute to around 12, and the metabolic rate drops to around 5 percent of the daytime resting value. To the touch the bird is cold; to the eye it is motionless on the perch, with the eyes closed and the bill tucked into the breast feathers. A torpid hummingbird that is handled does not respond.
By dawn the temperature climbs and the flowers begin to open, and the bird begins to shiver itself back to working temperature, drawing on the last of the fat reserves to power the muscle activity that generates the rewarming heat. Body temperature rises at around 1 degree per minute, and the full transition from torpor to flight-ready takes around 20 minutes. The first flight of the day is to the nearest flower, with the bird flying on near-empty reserves and unable to defer the meal, and a hummingbird that fails to find food in the first hour after waking does not survive the next night. Torpor is rare in birds outside the swift-and-hummingbird group; the only other species to use it routinely are the common poorwill (Phalaenoptilus nuttallii), which can stay torpid for weeks in winter, and a handful of other nightjars and swifts.
Migration: 800 km Non-Stop Across the Gulf of Mexico
For a bird with the energy demands of a hummingbird, long-distance migration looks structurally impossible, and yet several species perform the longest non-stop crossings made by any bird of comparable size.
The ruby-throated hummingbird (Archilochus colubris) breeds across the eastern United States and southern Canada and winters in Central America; many individuals make the southbound journey by crossing the Gulf of Mexico in a single non-stop flight from the Louisiana or Florida coast to the Yucatán Peninsula. The crossing is around 800 km of open water, takes around 18 to 22 hours of continuous wingbeat, and offers no surface to land on along the way.
The bird prepares by feeding through every daylight hour for around two weeks before departure and almost doubles its body mass, from a normal 3 to 3.5 g to a pre-migration 5.5 to 6.5 g, with the extra weight stored as subcutaneous fat. The fat is the fuel for the crossing; a bird that arrives on the far shore is back to its starting weight and is looking for the next flower before it has even landed. The rufous hummingbird (Selasphorus rufus) makes the longest migration of any species, breeding in Alaska and wintering in Mexico, a round trip of around 6,400 km and the longest migration relative to body length of any bird in the world.
Hummingbird vs Swift vs Sunbird: Anatomy Comparison
The closest living relatives of hummingbirds are the swifts, also in the order Apodiformes; the closest ecological analogue is the sunbird, an Old World nectar feeder in the order Passeriformes that has arrived at the same flower-feeding niche from a different starting point. The body plans of the three groups overlap in some places and diverge in others.
| Feature | Hummingbird | Swift (close relative) | Sunbird (Old-World nectar feeder) |
|---|---|---|---|
| Order | Apodiformes | Apodiformes | Passeriformes |
| Range | Americas only | Worldwide | Africa, Asia, Australia |
| Hover | Sustained, indefinite | Brief, not sustained | Brief, not sustained |
| Wingbeat shape | Figure of eight; shoulder rotates 180 degrees on each beat | Up and down with shoulder rotation; lift mainly on downstroke | Standard up-and-down bird wingbeat; lift on downstroke only |
| Flight muscles (% body mass) | 25 to 30% | 20 to 25% | ~15% |
| Heart rate (active flight) | 1,000 to 1,260 bpm | ~600 bpm | ~600 bpm |
| Tongue | Forked pump that cycles 15 times a second | Standard short tongue | Brush-tipped tongue, no pump action |
| Diet | Nectar and small insects | Aerial insects only | Nectar and insects (perches to feed) |
| Feet | Tiny; cannot walk | Tiny; cannot walk | Standard perching feet; walks short distances |
| Nightly torpor | Routine in cold conditions | Used by some species | Rare |
For more on individual hummingbird species, see Hummingbird Species: A List of All 361 Hummingbird Types. For broader bird anatomy, see Bird Anatomy, Bird Feathers, Bird Beaks and Bills, and the Birds hub. For comparable raptor and seabird anatomy, see Eagle Anatomy, Owl Anatomy, and Penguin Anatomy. Browse the full Animal Anatomy hub for comparable species.