H OMING IN on a stoplight-bright patch of California fuchsia blossoms, an Anna’s hummingbird prepares to feast on nectar In exchange the humming- bird unknowingly will carry pollen to fertilize another fuchsia.
Bird and flower are a perfect match. The hummingbird’s long bill can probe deeply into the fuchsia’s narrow tube of petals, the corolla (above). As the tongue touches bottom, pollen from the plant’s male organs, the stamens, sticks to the bill and chin feathers. When the bird drinks from the next fuchsia, it deposits the fertilizing pollen on the blossom’s female organ, the pistil, and receives from its stamens a fresh load of pollen, thus continuing the cycle. The blossom’s design usually excludes other nectar feeders, such as bees, which are less efficient pollinators since they light on many kinds of flowers and would waste the fuchsia’s pollen on competing species.
All of the more than 300 species of hummingbirds feed primarily on nectar and therefore serve as important pollinators. In southern California photographer Robert Tyrrell and I, with support from the Harry Frank Guggenheim Foundation,
have studied several species and their host flowers.
STOICALLY bearing the burdens of motherhood, a female Anna’s hummingbird incubates her coffee-bean-size eggs, normally two to a clutch (above). During seasonal blooming, females arrive at nectar patches that males aggressively defend from rivals. After mating, the female leaves her mate’s territory to seek her own source of nectar and build a nest of plant fiber and lichens bound with spider webbing. Initially, she has time to patrol her nectar stake. But after two weeks her eggs hatch and the nestlings demand more of her time.
As competitors invade her territory, she must scrounge insects and rob the nectar supplies of others for her young. Her own requirements call for a daily ration of nectar greater than her body weight. After four weeks the fledglings of the closely related Costa’s hummingbird are ready to leave the nest. Duller plumage helps females blend more effectively into the dry, shrubby chaparral, fraught with potential predators such as scrub jays and gopher snakes.
SPECIALIZATION enhances the odds for flowers in the chaparral. Tree tobacco, an Argentine import, has leaves armed with toxic nicotine to deter plant-eaters. But during late summer its blossoms provide welcome flasks of nectar for Anna’s hummingbirds A rufous hummingbird feeds from another wild flower,
Penstemon labrosus right). The flower’s upper lip has been bent back to illustrate how the stamens give the bird a dusting of pollen
A black-chinned hummingbird shows how woolly blue curls compensate for shallow corollas with extra-long reproductive organs. As the bird rises to blot up the last droplet of nectar, it bumps the stamens and pistil. Often hidden in such lifegiving exchanges are tiny mites that also drink the flowers’ nectar. For a continuous food supply, they must find a way from blossom to blossom. How?
The hitchhiking mites race up the bills of feeding hummingbirds, stow away in their nostrils, then race down into the next flower---intriguingly effective daptations in an
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