Arizona-Sonora Desert Museum Digital Library

Distinguishing Features

Rufous Hummingbird is 3½ (9 cm) inches in length; 3 g to 4 g in weight. The male is cinnamon-rufous on the upper parts, tail, and lower breast and belly. In good light, the throat iridesces a metallic orange to scarlet. The female is iridescent bronze-green above and dull white below. She also has a cinnamon wash to the flanks and much rufous on all the tail feathers.

Habitat

Rufous hummingbird breeds in the northwestern United States and western Canada and winters in Mexico. It tends to migrate north through western Sonora, western Arizona, to the Pacific coast; it tends to migrate south through the Rocky Mountains, including eastern Arizona. This annual migration path forms a broad oval over most of western North America. The males generally migrate before females and immatures. During migration in Arizona and Sonora, the Rufous uses a wide variety of habitats from desertscrub to mountain meadows, wherever there are flowers or feeders.

Hummingbirds occupy most temperate and tropical habitats in the western hemisphere. In our region, they can be found in desert, grassland, woodland, and forest. They tend to prefer edges of dense habitats, and the scrubbier areas of open habitats.

Feeding

Hummingbirds are the dominant nectarivorous birds in the western hemisphere. Old World ecological equivalents include the honey-eaters of Australia and the sunbirds of Africa. Although many of these other birds may have specialized bill shapes and foot types for getting nectar, and some have bright or iridescent plumage, none achieve the specialization to nectarivory that the hummingbird has. Hummingbirds also eat many small, soft-bodied arthropods.

Life History

In our region, the Rufous is known only as a migrant and a very pugnacious hummer at feeders. Rufous Hummingbirds, southbound from nesting grounds in the northwest U.S., may appear in the Sonoran Desert by July, along with lesser numbers of other species, to joust for space around the blooms that follow the summer rains.

North American hummingbirds are highly territorial, both sexes protecting feeding territories, males protecting courtship territories, and females protecting nesting territories. These territories are protected by displays, songs, chases, or the mere presence of the hummer on an exposed perch.

Hummingbirds are promiscuous breeders. The male merely courts and mates with receptive females. The female may mate with more than one male, but she alone builds the nest, lays and incubates the eggs, and broods and tends the young.

The nest is not much larger than a jigger glass. It is typically composed of fibrous plant down or seeds and mosses, bound together and to a branch with spider webbing. The nest may be lined with hair or feathers and decorated with leaves, bark strips, or lichens, depending on the species.

Only two bean-sized eggs are laid and incubated for about two weeks, depending on the species.

Young are altricial and are fed a mixture of nectar and small, soft-bodied arthropods like spiders and gnats. They fledge in about three weeks depending on the species and to some extent on the weather.

Like many animals, most hummingbirds die during their first year. After that, their life expectancy may increase to three or four years. Few live past this, although there is a record of a Broad-tailed Hummingbird living eleven years.

Describing hummingbirds without resorting to superlatives would be difficult, and hardly fair. This family includes the world's smallest birds, with the most brilliant iridescent colors, the fastest wingbeats, and the most amazing ability to fly up, down, sideways, and backwards. They spend their days hovering at flowers to sip nectar, feeding almost constantly to supply the sugar necessary to maintain their racing metabolism. Many people would call these the world's most fascinating birds.

The brightest colors and most ornate patterns among hummingbirds are worn by males, and the purpose is evidently to impress females. After mating, the male takes no more part in family life. The female alone builds the nest, incubates the tiny eggs, and feeds the young. Considering the amount of energy that an individual hummingbird needs just to feed itself, it seems remarkable that the female is able to raise the young successfully all alone.

There are well over three hundred species of hummingbirds, all native to the Americas. The vast majority, not surprisingly, are found in the tropics, where flowers abound year-round. Only a handful of species reach the United States; southern Arizona hosts more than a dozen of those.

In our region, they range in length from 2½ inches to 5 inches (7 to 13 cm), and from 2 g to 10 g in weight. All in our region have long, pointed beaks for probing flowers for nectar, saber-like wings for hovering in front of flowers, a generally iridescent bronze or green dorsal surface, and primarily in males, bright, colorful throat and head patches. The iridescent throat patch is called the gorget (pronounced gore-jet).

Costa's Hummingbird is the only true desert hummer here, but several others live along the desert's edges. Black-chinned and Broad-billed Hummingbirds nest in streamside woods in summer, while Anna's Hummingbird, a recent invader from California, nests in the same areas (and in residential neighborhoods) in winter. Our region hosts the greatest variety of hummers in late summer, when several species are on their way south.

Hummer Facts

• Hummingbirds' hearts are larger in proportion to body size than those of any other warm-blooded animal.
• Hummers have the most rapid heart rate for a bird: up to 500 beats per minute at rest and 1260 beats per minute during activity.
• Their flight muscles account for 25 to 30 percent of body weight, compared to 15 to 25 percent in other strongly-flying birds.
• Hummers have the most rapid wing beats of birds: up to 80 beats per second.
• Their unique flight mechanisms allow them to hover for long periods of time, move in any direction (even backwards), and dive at over 60 miles per hour during displays.
• They have high body temperatures: 105° to 109°F (40.5° to 42.5°C).
• They have the ability to become torpid at night.
• Hummingbirds may consume 70 percent of their body weight, in solid food per day (8 to 12 calories) and 4 to 8 times their body weight, in water.
• There are over 300 species of hummingbirds. They live exclusively in the Western Hemisphere, from Alaska to the tip of South America.

Powering Down

Being a hummingbird is like driving a car with a one-gallon gas tank: there is an almost constant need to refuel. Hummingbirds are often perilously close to the limits of their energy reserves. On cold nights, when the costs of keeping warm are especially high, it may be too risky for a hummingbird even to keep its engine idling.

At such times, a hummingbird bristles its feathers to let its body heat escape, and its temperature quickly approaches that of its surroundings. Its heart rate drops dramatically and it may stop breathing for minutes at a time. It appears lifeless, clinging motionlessly to its branch with its head drawn close to its body and its bill pointing sharply upward. At daybreak it revs its metabolic engines and warms itself again.

This sort of temporary hibernation is called torpor. Hummingbirds become torpid not only to deal with fuel crises, but also to save energy for migration. And since birds lose moisture with every breath, becoming torpid also helps desert hummingbirds conserve water.