any
of about 320 species of small, often brightly coloured birds
of the family Trochilidae, usually placed with the swifts
in the order Apodiformes but sometimes separated in their
own order, Trochiliformes. The brilliant, glittering colours
and elaborately specialized feathers of many species (usually
of the males only) led the 19th-century British naturalist
John
Gould to give many hummingbirds exotic common names, many
of which are still in use—e.g., coquette, fairy,
hill star, wood star, sapphire, topaz, sun gem, and sylph.
Hummingbirds
are restricted in distribution to the New World, where the
greatest variety and number of species occur in South America.
About 12 species are found regularly in the United States
and Canada. Only the ruby-throated hummingbird (Archilochus
colubris) breeds in eastern North America, where it
is found from Nova Scotia to Florida. The northernmost hummingbird
is the rufous (Selasphorus rufus), which breeds from
southeastern Alaska to northern California.
All
hummingbirds are small, and many are minute. Even the largest,
the giant hummingbird (Patagona gigas) of western
South America, is only about 20 cm (8 inches) long, with
a body weight of about 20 g (2/3 ounce),
less than that of most sparrows. The smallest species, the
bee hummingbird (Mellisuga, sometimes Calypte,
helenae) of Cuba and the Isle of Pines, measures slightly
more than 5.5 cm, of which the bill and tail make up about
half. Weighing about 2 g, this species is the smallest living
bird and ranks with the pygmy shrews as the smallest of
warm-blooded vertebrates.
Hummingbirds
have compact, strongly muscled bodies and rather long, bladelike
wings that, unlike the wings of other birds, articulate
(connect) to the body only from the shoulder joint. The
architecture of the wing permits hummingbirds to fly not
only forward but also straight up and down, sideways, and
backward and to hover in front of flowers as they obtain
nectar and insects from them. The rate at which a hummingbird
beats its wings is the same during directional and hovering
flight. It varies with the size of the bird—the larger the
bird, the lower the rate. Consequently, the smallest hummingbirds
have extremely rapid wing-beat rates. In Calliphlox amethystina,
one of the tiniest species, the male has a wing-beat rate
of about 80 per second; the female, which is larger, beats
her wings at a rate of about 60 times per second. The ruby-throated
hummingbird has a wing-beat rate of about 70 per second
in the male and about 50 per second in the female. The rate
is much lower in the larger hummingbirds; the giant hummingbird,
for example, beats its wings only about 10 times per second.
In fact, the larger hummingbirds appear to beat their wings
more slowly than do other birds of comparable size.
The
hummingbird's body feathers are sparse and often strongly
metallic and rather scalelike in appearance. The sexes are
alike in appearance in a few species but are different in
most species; males of the latter species display a variety
of brilliance and ornamentation rivaled only by birds-of-paradise
and certain pheasants. The most typical badge is the gorget,
a bib of iridescent feathers the colour of which depends
on the viewing angle. Other specializations include crests;
abbreviated or thickened shafts of wing feathers; spatulate,
wiry, or flaglike tail feathers; and “pantaloons,” tufts
of puffy feathers on the thighs (usually white).
The
hummingbird's bill, which is adapted for securing nectar
from certain types of flowers, is usually rather long and
always slender . In the thornbills (Ramphomicron
and Chalcostigma), it is quite short, but in the
sword-billed hummingbird (Ensifera ensifera), it
is unusually long, contributing more than half of the bird's
21-centimetre length. The bill is slightly downcurved in
many species, strongly so in the sicklebills (Eutoxeres);
it is turned up at the tip in the awlbill (Avocettula)
and avocetbill (Opisthoprora).
Most
of the species that have been adequately studied do not
show pair-bond formation. In the violet-ears (Colibri)
and a few others, pair bonds are formed, and both sexes
assume parental duties. In the majority of other species,
the male defends a territory, where he displays in flight
to passing females with swoops, dashes, and sudden stops
and starts. Often he hovers in front of the female, oriented
so that the light reflects the colour of his gorget. Territorial
males chase off hummingbirds of their own and other species
and dive at large birds, such as crows and hawks, and even
at mammals, including humans. Most hummingbirds, especially
the smaller species, have scratchy, twittering, or squeaky
songs. In their U-shaped display flights, however, the wings
often produce humming, hissing, or popping sounds, which
apparently function much as do the songs of other birds.
In many species the tail feathers produce the sounds.
The
hummingbird's nest is a tiny cup of plant fibres, spider
webs, lichens, and moss that is attached to a branch, a
forked twig, a large leaf, or a rock ledge. In certain species
known as hermits (Phaethornis), the nest is hung
by a narrow stalk from the underside of a ledge or from
the roof of a cave or culvert; the nest cup, set on one
side of a mass of mud and plant material, is held level
by careful weighting of the other side of the mass.
The
two elliptical white eggs (rarely, one) are the smallest
laid by any bird, although, proportionately, they are equal
to about 10 percent of the female's body weight. They are
incubated for about 15 to 20 days. The young, hatched blind
and virtually naked, are fed by regurgitation and fledge
in about three weeks; the time from laying to fledging apparently
is correlated with food supply.