Do Hummingbirds Hum?: Fascinating Answers to Questions about Hummingbirds

FOUR: Reproduction

FOUR Reproduction Question 1: How does a hummingbird attract a mate? Answer: Many hummingbird species are dimorphic, meaning that the male and female have different plumages, with the female generally being less colorful. The males use the bright, iridescent plumage on the gorget, crown, or front of their body to attract a mate. Many species have specially developed tail feathers or a crest on the head that may serve to convince a female that this male is a stronger and more fit mate than his competition. James Clark of the University of California, Berkeley, filmed Anna’s Hummingbirds performing courtship displays, and he noted that they orient the display dive in relation to the sun, so that they “look like a little magenta fireball dropping out of the sky.” This extreme behavior offers the brightest possible image to a receptive female in order to chase her to her nesting area so they can mate. Males fly up high and typically plunge ten or fifteen times in a row toward the female. Clark’s analysis of the dives indicates that their maximum speed reaches about 385 body lengths per second, making them the world’s fastest bird. When they pull up to stop the dive, they experience a pull that is nine times the force of gravity, matched only by the speed of a jet fighter pilot doing aerial maneuvers. The birds can survive this incredible speed without trauma only because they maintain it for less than 0.3 seconds. 70 DO HUMMINGBIRDS HUM? In many North American hummingbird species, males approach perched females with loud chattering or other vocal sounds. In mating behavior that was first described by Stephen Russell, a hummingbird research ornithologist from the University of Arizona, the female leads the male into the area where she has constructed her nest; when she perches, the male may attempt to copulate or, if the female is not ready, he may begin emitting loud courtship calls and/or initiate a shuttle display (see figure 17). The female may follow the actions of the male, pointing at him with her bill, but if she is not ready or decides not to mate, she flies away. In some cases, an aggressive male tries to compel a less receptive female to copulate by forcing her to the ground (see also this chapter, Question 4: How do hummingbirds reproduce?). Males of many hermit species (usually less conspicuously colored), as well as some brightly colored trochilids, gather in groups, called leks, where they sing and display for females that visit the lek to choose a mate. Male animals of many species gather in a lek to attract females, including some other birds, some insects, certain fish, some bats, and other mammals. A Figure 17. Diagram of the shuttle display of a male Anna’s Hummingbird Calypte anna. The bird hovers, moving left and right in a short arc above the female. REPRODUCTION 71 few examples of the extensive research on the behavior of hummingbirds in leks will give you an idea of what may occur. MarcoPizoandWesleySilvaobservedthatSwallow-tailedHummingbirds Eupetomena macroura in Sao Paolo, Brazil, gather in groups of from six to fifteen individuals and sing together briefly before and after sunrise. Sooty-capped Hermits Phaethornis augusti , studied by Carol Ramjohn and her colleagues in Venezuela, collected in smaller groups. While they are in the lek, they sing approximately 75 percent of the time, mostly in the early morning and late afternoon. Green Hermits Phaethornis guy observed byElizabethMacDougall-ShackletonandHeidiHarbisoninPanama formed leks of about a dozen males that sing in subgroups, spending more time singing if they are near the center of the lek. Sandra Gaunt of Ohio State University found that male Green Violet-ears Colibri thalassinus sing so cooperatively that from a distance it sounds as if only one bird is singing. This fascinating phenomenon demonstrates a highly organized method of attracting a mate. Leks are probably more popular among hermits because they lack the colorful plumage with which to attract the attention of females, so they use their voices in a dramatic way. Question 2: How do hummingbirds protect their mating territory? Answer: During the mating season, male hummingbirds do all they can to drive away competing males. The defending male uses loud noises, threatening postures, and aggressive actions to scare off rivals and any other birds that invade its feeding or courtship territory. The male sings, perched in an exposed position with...