small animal is the only species of hummingbird that regularly nests east of the Mississippi River in North America.
The Ruby-throated Hummingbird is the smallest bird species that breeds in the Eastern United States and Eastern Canada. This hummingbird is from 7 to 9 cm (2.8 to 3.5 in) long and has a 8 to 11 cm (3.1 to 4.3 in) wingspan. Weight can range from 2 to 6 g (0.071 to 0.212 oz), with males averaging 3.4 g (0.12 oz) against the slightly larger female which averages 3.8 g (0.13 oz). Adults are metallic green above and greyish white below, with near-black wings. Their bill, at up to 2 cm (0.79 in), is long, straight and very slender. As in all hummingbirds, the toes and feet of this species are quite small, with a middle toe of around 0.6 cm (0.24 in) and a tarsus of approximately 0.4 cm (0.16 in). The Ruby-throated Hummingbird can only fox-trot if it wants to move along a branch, though it can scratch its head and neck with its feet.
The species is sexually dimorphic. The adult male has a gorget (throat patch) of iridescent ruby red bordered narrowly with velvety black on the upper margin and a forked black tail with a faint violet sheen. The red iridescence is highly directional and appears dull black from many angles. The female has a notched tail with outer feathers banded in green, black, and white and a red throat that may be plain or lightly marked with dusky streaks or stipples. Males are smaller than females and have slightly shorter bills. Juvenile males resemble adult females, though usually with heavier throat markings. The plumage is molted once a year, beginning in late summer.
The breeding habitat is throughout most of eastern North America and the Canadian prairies, in deciduous and pine forests and forest edges, orchards, and gardens. The female builds a nest in a protected location in a shrub or a tree. Of all hummingbirds in the United States, this species has the largest breeding range.
The Ruby-throated Hummingbird is migratory, spending most of the winter in southern Mexico and Central America, as far south as extreme western Panama, and the West Indies. It breeds throughout the eastern United States, east of the 100th meridian, and in southern Canada in eastern and mixed deciduous forest. In winter, it is seen mostly in Mexico.
Ruby-throated Hummingbirds are solitary. Adults of this species are not social, other than during courtship (which lasts a few minutes); the female also cares for her offspring. Both males and females of any age are aggressive towards other hummingbirds. They may defend territories, such as a feeding territory, attacking and chasing other hummingbirds that enter.
As part of their spring migration, portions of the population fly across the Gulf of Mexico. This feat is impressive, as a 800 km (500 mi), non-stop flight over water would seemingly require a caloric energy that far exceeds an adult hummingbird’s body weight of 3 g (0.11 oz). However, researchers discovered the tiny birds can double their lean mass in preparation for their Gulf crossing. The additional mass, stored as fat, provides enough energy for the birds to achieve the flight.
They feed frequently while active during the day. When temperatures drop, particularly on cold nights, they may conserve energy by entering hypothermic torpor.
Hummingbirds have many skeletal and flight muscle adaptations which allow the bird great agility in flight. Muscles make up 25–30% of their body weight, and they have long, blade-like wings that, unlike the wings of other birds, connect to the body only from the shoulder joint. This adaptation allows the wing to rotate almost 180°, enabling the bird to fly not only forward but fly backwards, and to hover in front of flowers as it feeds on nectar, or hovers mid-air to catch tiny insects. Hummingbirds are the only known birds that can fly backwards.
During hovering, (and likely other modes of flight) ruby-throated hummingbird wings beat 55 times per second.