Hummingbird

Hummingbirds are about 320 species of small, often brightly coloured birds in the family Trochilidae, usually placed with the swifts in the order Apodiformes. They are restricted to the New World, where their greatest variety occurs in South America, and about 12 species are found regularly in the United States and Canada.

Hummingbirds are defined by smallness, and the extremes of the family are extremes of miniature scale. The bee hummingbird of Cuba and the Isle of Pines measures slightly more than 5.5 cm, weighs about 2 g, and is the smallest living bird ^{1Hummingbird · Encyclopaedia Britannica ↗}. Even the largest hummingbird, the giant hummingbird of western South America, is only about 20 cm long and weighs about 20 g, less than most sparrows ^{1Hummingbird · Encyclopaedia Britannica ↗}. Across the family, typical body mass falls between 2.5 and 6.5 g ^{2Trochilidae (hummingbirds) · Animal Diversity Web, University of Michigan Museum of Zoology ↗}.

The giant hummingbird's size is matched by the altitude it tolerates. It can live in the Andes Mountains at elevations over 14,000 feet, higher than many helicopters can fly, and has evolved hemoglobin-rich blood ^{3Uncovering the Secrets Behind Hummingbirds' Extreme Lifestyle · Smithsonian Magazine ↗}. The bee hummingbird, at the other pole, weighs only 1.95 grams, so theoretically 16 of them could be mailed first-class using just one stamp ^{4Hummingbirds · Smithsonian's National Zoo and Conservation Biology Institute ↗}.

Form follows function in the bill and the wing. Hummingbird bills vary widely in shape, and bill length and shape often indicate which flowers a species feeds on, while extendable bifurcated tongues extract the nectar ^{2Trochilidae (hummingbirds) · Animal Diversity Web, University of Michigan Museum of Zoology ↗}. The wings connect to the body only at the shoulder joint, an architecture that lets them fly straight up and down, sideways and backward and to hover at flowers ^{1Hummingbird · Encyclopaedia Britannica ↗}. In most hummingbird species the sexes look different, and the male's most typical badge is the gorget, a bib of iridescent feathers whose colour depends on the viewing angle ^{1Hummingbird · Encyclopaedia Britannica ↗}.

Hummingbirds possess numerous skeletal and flight muscle adaptations for hovering and high maneuverability, and they are the only birds that truly hover and fly both forward and backward. Their wings beat about 70 times per second in direct flight, and while diving the rate rises above 200 times per second. This fast, darting flight can generate G-forces high enough to black out a fighter pilot.

Nectar cannot be too concentrated and sticky because hummingbirds rely on a long, tube-like tongue that draws it into their mouths through wicking action, like water rising in a straw. They gain extra amino acids from pollen and protein from insects, which they catch by hawking or hover-gleaning.

Because hummingbirds cannot feed at night, they depend on endogenous body fat stores, and torpor is the state that carries them through. It is a very deep, sleep-like condition of minimal metabolism and very low body temperature, available to them on any night of the year, and it differs from hibernation, a longer form of torpor lasting days or weeks. Torpor is not sleep, because animals in torpor do not get the benefits of sleep: they are not clearing toxins from the brain or repairing tissue, so the state is a much deeper energy saving.

On cold nights torpor saves up to 95 percent of hourly metabolic cost. Heart rate falls from more than 1,200 beats per minute in flight to as low as about 40 beats per minute in torpor.

Studies found that larger species use torpor less often because they can carry more fat and dominate feeders, chasing smaller species away. In summertime the birds entered torpor at very consistent fat levels, about 6% body fat, which supports the idea that hitting a critically low fat threshold triggers torpor. Across 108 nights of recording at roughly 10 nests, only one nesting hummingbird used torpor, and only on two nights.

Hummingbirds are nectivores and insectivores, taking roughly 90 percent of their diet from nectar and 10 percent from arthropods such as flies, wasps, spiders, beetles and ants.

They drink up to twice their body weight per day.

A nectar-rich diet gives them blood-sugar levels that would put a person in a coma. Hummingbirds cope with a huge sugar onslaught by having leaky guts that let sugars pass between cells, allowing blood sugar levels as much as six times higher than those seen in people. They are remarkably nimble at switching their metabolism from burning sugar to burning fat, an enormous biochemical shift that happens in mere minutes, far faster than other organisms manage.

Female Ruby-throated Hummingbirds build their nests on a slender, often descending branch, usually of deciduous trees, and place them 10-40 feet above the ground. The nest is made of thistle or dandelion down held together with strands of spider silk and sometimes pine resin, and the female stamps its base to stiffen it while the walls stay pliable as the chicks grow.

A male Ruby-throated Hummingbird performs a looping U-shaped courtship dive that can start from 50 feet above the female, then switches to fast side-to-side flights if she perches.

Hummingbirds that breed in North America overwinter in Mexico, following migration corridors along the coasts, the Rockies or across the Gulf of Mexico in non-stop flights of 18 to 22 hours timed to spring flowering.

Ruby-throated Hummingbirds keep body mass low during the breeding season for aerial agility, then fatten up in late summer to fuel their long migration south as far as Central America.

Ruby-throated Hummingbirds are commonly associated with old fields, forest edges, meadows, orchards and backyards, and on their tropical wintering grounds they live in dry forests, citrus groves, hedgerows and scrub.

Hummingbirds are amazingly adapted pollinators whose long slender bills and tube-like tongues let them drink nectar from brightly-colored flowers, fueling the energy needs of their high metabolism. Plants that rely on hummingbirds for pollination instead of insects have often acquired sucrose-rich nectar and flowers that are brightly colored but unscented. Adult hummingbirds have few predators, though snakes, forest falcons and pygmy-owls take them, while nest predators such as jays, toucans and some bats are the biggest threat.

The International Union for Conservation of Nature's Red List of Threatened Species lists 20 hummingbird species as endangered or critically endangered and 54 species in high-risk categories.

Ruby-throated Hummingbird populations increased every year between 1966 and 2019 while Partners in Flight estimates a global breeding population of 36 million, rating the species of low conservation concern.

National parks make ideal hummingbird refuges because they hold large expanses of forest for breeding and nesting, and their pesticide-free native plants are excellent food sources.

Huitzilopochtli, also called Hummingbird of the South and Blue Hummingbird on the Left, was the supreme god of the Mexica and the Aztec god of the sun and war. Aztec belief held that the spirits of fallen warriors returned to earth as hummingbirds and accompanied Huitzilopochtli on the first half of his journey across the sky. In Aztec art he was symbolised by the hummingbird, called huitzilin, whose feathers he wore in his helmet, or by an eagle on a prickly pear cactus.