National Geographic : 1951 Aug
248 Lights! Action! Camera! Pushed from Nest, a Feathered Star Performs Reluctantly Inquisitive humans and their gear failed to disturb this nesting Broad-tailed Hummingbird. Poked gently by R. J . Niedrach, she took off on a short flight (page 247). Walker Van Riper operated the camera. a second, there is little or no sound. The chatter becomes distinctly audible in level flight when the beat rises to 75 or higher, and is loudest in the "dive-bombing" courtship display, when the wings reach a rate of 200. Our pictures of male and female Broad-tail wings in actual flight reveal the source of the sound for the first time. When flying, the female makes only the usual buzzing, or hum ming, sound. The photograph of her spread wing shows that all the primary feathers are normally shaped (page 247). Not so with the male; his first two, or outermost, primaries are uniquely modified, narrowing at the tips to produce the slots shown in the picture (page 251). Air fluttering through these slots pro duces the rattling whistle. In migration male Broad-tails usually pre cede the females, arriving in Denver about the middle of May. This species (and apparently a number of others) is highly matriarchal. The late Frank Bene's observations indicate that the female Black-chinned Hummingbird selects her nesting area and begins to build the nest before searching for a mate. When she finds him, she completes the nest, lays the two white eggs, incubates them herself, and cares for the young until they are ready to fly and feed themselves. Our observations of the Broad-tail, while limited, seem to show that it follows the same schedule. Nests of the Broad-tail average a little over 1\2 inches in outside diameter and somewhat less in height. The inner cup, about an inch in depth and diameter, is lined with soft plant down, often from willow and cottonwood seeds; feathers are rarely used. Lichens, dry leaves, and fibers, bound together with spider webs, form the outer shell. Always the outer layers of the nest are camouflaged in color and texture to match the supporting limb (page 256). This hummer nests not only in the moun tains up to 10,000 feet but-conveniently for picture takers-also in the cities. Hummingbirds Have Twins Hummingbirds lay only two eggs. Those of the Broad-tail hatch in about 14 days. The young, born helpless, naked, black, and blind, are about the size of honeybees. They are fed by regurgitation, the mother thrusting her bill down the baby's gullet with a convulsive spasm (opposite and page 256). Besides nectar, the food consists of small spiders and insects gleaned from flowers or caught in the air.