Ruby-throated hummingbirds are tiny colorful birds that breed in North America. Adults are metallic green above and grayish white below, with near-black wings. 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 female has a notched tail with outer feathers banded in green, black, and white and a white 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 bill of these birds is long, straight, and very slender. Their toes and feet are quite small.
Ruby-throated hummingbirds breed throughout most of the Eastern United States and south-central and southeastern Canada. These are migratory birds spending most of the winter in Florida, southern Mexico, and Central America, as far south as extreme western Panama, and the West Indies. Ruby-throated hummingbirds live in mixed deciduous and broadleaved forests, pine forests and forest edges, orchards, and gardens.
Ruby-throated hummingbirds are solitary and interact with each other only during the breeding season. Both males and females of any age are aggressive toward other hummingbirds. They may defend territories, such as a feeding territory, attacking and chasing other hummingbirds that enter. Ruby-throated hummingbirds feed frequently while active during the day. They feed from flowers using a long, extendable tongue and catch insects on the wing or glean them from flowers, leaves, bark, and spiders' webs. When temperatures drop, particularly on cold nights, they may conserve energy by entering hypothermic torpor. Ruby-throated hummingbirds communicate with rapid, squeaky chirps, which are used primarily for threats. For example, males may vocalize to warn another male that has entered his territory.
Ruby-throated hummingbirds are thought to be polygynous. However, polyandry (females have multiple mates) and polygynandry (both males and females have multiple mates) may also occur. The breeding season takes place in March-July. Males arrive at the breeding area in the spring and establish a territory before the females arrive. When the females return, males court females that enter their territory by performing courtship displays. They perform a "dive display" rising above the female. If the female perches, the male begins flying in very rapid horizontal arcs in front of her. If the female is receptive to the male, she may give a call and assume a solicitous posture with her tail feathers cocked and her wings drooped. During the courtship displays, the male makes a rapid 'tik-tik tik-tik tik-tik' sound with his wings. The sound is produced both during the shuttle display, at each end of the side-to-side flight. Also, the sound is made during dive displays. The nest is usually constructed on a small, downward-sloping tree limb or in a shrub and is well camouflaged. It is composed of bud scales, with lichen on the exterior, bound with spider's silk, and lined with fibers such as plant down (often dandelion or thistle down) and animal hair. Old nests may be occupied for several seasons, but are repaired annually. As in all known hummingbird species, the female alone constructs the nest and cares for the eggs and young. She lays 1 to 3 white eggs and produces one or two broods each summer. Incubation lasts about 10 to 14 days. The female broods the chicks over a period of 12-14 days, by which point they are feathered and homeothermic. When the chicks are 18 to 22 days old, they leave the nest and make their first flight.
Ruby-throated hummingbirds are threatened by climate change that affects their migration patterns and by habitat loss due to agricultural growth and deforestation. They also suffer from predation by raptors and domestic cats and from collisions with windows.
According to the University of Michigan (Museum of Zoology) resource, the total population size of the Ruby-throated hummingbird is 7,300,000 individuals. According to the All About Birds resource the total breeding population size of the species is 20 million breeding birds. Overall, currently, Ruby-throated hummingbirds are classified as Least Concern (LC) on the IUCN Red List and their numbers today are increasing.
While collecting nectar from flowers, Ruby-throated hummingbirds transfer the pollen and assist in plant pollination in their local ecosystem.