4 minute read


Biology Of Hummingbirds

Hummingbirds have small, weak legs and feet, which are used only for perching, and not for walking. Hummingbirds only move about by flying, and they are extremely capable aerial acrobats. Although diminutive, hummingbirds can fly quickly over short distances, at up to 31-40 miles per hour (50-65 kph). Hummingbirds can fly forwards, backwards, and briefly, upside down. These birds are also very skilled at hovering, which they typically do when feeding on nectar from flowers. Hovering is accomplished using a figure-eight movement of the wings, and a relatively erect posture of the body.

Because of their small size, the tiniest hummingbirds must maintain an extraordinarily rapid wingbeat rate of 70 beats per second to stay aloft. However, the larger species can fly with only about 20 beats per second. The flight muscles of hummingbirds typically account for 25-30% of the body weight, compared with an average of 15% for other birds.

Also as a direct result of their small body size, hummingbirds have a high rate of heat loss from their bodies. This is because small objects, including small organisms, have a relatively large surface area to volume ratio, and lose heat more rapidly from their surface than do larger-bodied animals. This relatively high rate of heat loss, combined with the fact that hummingbirds are very active animals, means that they have a very high rate of metabolism. Consequently, hummingbirds must feed frequently, and relatively voraciously, to fuel their high-energy life style.

When weather conditions make it difficult for them to forage, for example, during intense rain or cool temperatures, hummingbirds may enter a state of torpor. This involves becoming inactive, and reducing and maintaining a relatively low body temperature, as a means of conserving energy until environmental conditions improve again.

Most hummingbirds feed on nectar, obtained from flowers. Feeding is usually done while hovering. All hummingbird species have long, slender bills that are specialized for this mode of feeding. The bill of the swordbill hummingbird (Ensifera ensifera) is straight, and is as long as the bird's body and tail, about 4 in (10 cm). This sort of extremely developed feeding device is adapted to extracting nectar from the base of long, tubular flowers, in particular, certain species of passion flower (Passiflora spp.) that have corolla tubes about 4.3 in (11 cm) long. A few species of hummingbirds, for example, the white-tipped sicklebird (Eutoxeres aquila), A hummingbird sipping nectar from a flower. Zefa Germany/Stock Market. Reproduced by permission. have downward curving beaks that are useful for probing flowers of other shapes.

Hummingbirds also have a long tongue that can be extended well beyond the tip of their bill. The tongue of hummingbirds has inrolled edges, that can be used to form a tube for sucking nectar.

Some tropical plants occur in a mutualistic relationship with one or several species of hummingbird, that is, a symbiosis in which both species receive a benefit. The advantage to the hummingbirds occurs through access to a predictable source of nectar, while the plant benefits by pollination. While feeding, the hummingbird will typically have its forehead dusted with pollen, some of which is then transferred to the receptive stigmatic surfaces of other flowers of the same plant species as the bird moves around while foraging. Hummingbird-pollinated flowers are usually red in color, and they have a tubular floral structure, with nectar-secreting organs at the base.

While nectar is the primary food of hummingbirds, they are also opportunistic predators of small insects, spiders, and other arthropods. This animal food is an important source of protein, a nutrient that is deficient in sugar-rich nectar.

The largest species of hummingbird is the giant hummingbird (Patagona gigas) of montane habitats in the Andes, up to 0.7 oz (20 g) in body weight and 8.5 in (22 cm) long, although about one-half of the length is the elongated tail of the bird. The smallest hummingbird is the bee hummingbird (Mellisuga helenae) of Cuba, with a body length of only 1 in (2.5 cm) and a weight of 0.07 oz (2 g). This is also the world's smallest species of bird. Most other hummingbirds are also small, typically about 2 in (5 cm) long.

Hummingbirds can be spectacularly colored, especially the males. Most of the coloration is not due to the presence of pigments, but to iridescence. This is a physical effect associated with prism-like microstructures of the feathers of hummingbirds and some other birds. These break light into its spectral components, which are selectively segregated into brilliant reds, pinks, blues, purples, and greens through absorption processes, and by the angle of incidence of light. The most vivid colors of hummingbirds are generally developed by the feathers of the head and throat, which are prominently displayed by the male to the female during courtship flights. The male birds of some species of hummingbirds also develop crests, and intricately long tail feathers.

Even the smallest hummingbirds can be quite aggressive against much larger birds. Because of their extraordinary mobility, hummingbirds can successfully chase away potential predators, such as small hawks and crows. Hummingbirds are also aggressive with other hummingbirds, of the same or different species. This can result in frequent and rowdy fights as territorial claims are stated and defended at good feeding stations.

Additional topics

Science EncyclopediaScience & Philosophy: Heterodyne to Hydrazoic acidHummingbirds - Biology Of Hummingbirds, North American Hummingbirds, Conservation Of Hummingbirds