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CALIFORNIA WILD

FEATURE STORY

Feathered Gems

luis felipe baptista

One early morning in 1964, I was on my way to observe a pygmy nuthatch (Sitta pygmaea) nest-building on a snag by a stream bank in Golden Gate Park, San Francisco. With the rising sun filtering down through a break in the leafy canopy, I looked down and saw what at first appeared to be a large lighted cigarette by the stream. It was the shiny throat, or gorget, feathers of a male Allen’s hummingbird (Selasphorus sasin). The hummer had come to the stream to bathe, and as it raised its head, a thin shaft of sunlight caught its gorget feathers, which created a cascade of shimmering golden orange-red. This was my first experience of hummingbirds flashing the colors of their display feathers, and I was hooked. Since then, I’ve studied hummingbirds in North America, Mexico’s tropical forests, Costa Rica, and Brazil.

The hummingbird family (Trochilidae) includes nearly 320 species and is found nly in the New World. These birds are mostly found in the tropics, the number of species increasing with decreasing latitude. Nineteen species are known in North America, while Ecuador boasts the highest number of species at 163. One, the rufous hummingbird (Selasphorus rufus) ranges as far north as Alaska, while the green-backed firecrown (Sephanoides sephanoides), has been found in Tierra del Fuego. This avian order includes the smallest birds in the world. A male Cuban bee hummingbird (Mellisuga helenae) weighs about two grams. At the other extreme is the Andean giant hummingbird (Patagona gigas), which weighs an average of 22 grams. Females of the smaller species tend to be larger than the males, whereas females of the larger species tend to be smaller than the males.

Although small insects and spiders provide protein and are especially important when the hummingbirds are feeding their young, nectar is the main diet of all hummingbirds. Hummingbirds are superbly adapted for feeding on flowers. They have long, thin bills and an extremely long tongue split near the tip. Each branch of the split is curled into a tube. The tongue is capable of considerable extension be-cause it’s attached to the hyoid apparatus, a long and flexible bony structure. In some species the hyoid apparatus extends under the skull and up and over the back of the head, splitting into two branches with each branch curling around an eye socket. In the magnificent hummingbird (Eugenes fulgens) a branch of the hyoid attaches behind the left nostril.

Hummingbirds are undoubtedly attracted to red. However, when given a choice between a red flower with little nectar and a blue or yellow flower with abundant nectar, a hummingbird will always select the latter. Recent studies have indicated that hummingbirds may also see in the ultraviolet range. When certain bee flowers were photographed with ultraviolet-absorbing film, it was found that elaborate patterns invisible to the human eye acted as guides to the nectarie—the flowers’ nectar-secreting glands. A hummingbird’s ability to see ultraviolet, like that of a bee’s, likely enables it to take advantage of these nectar-guides to locate a food source.

Hummingbirds have enormous breast muscles, which may make up some 30 percent of their body weight. These muscles elevate their wings and are responsible for generating power during both the upstroke and downstroke. Biologist Paul Johnsgard of the University of Nebraska reported that the wings of smaller hummingbird species may beat as many as 80 times per second during normal flight and accelerate to 200 times per second during courtship. A hummingbird is capable of flying backwards, forwards, or sideways with equal ease, and with rapid wing beats, it can hover by a flower while its tongue darts in and out of the corolla.

While I was conducting fieldwork in the rainforest of Hitoy Cerere in Costa Rica, I watched a pygmy hermit hummingbird (Phaethornis longuermareus) fly along a forest edge in a straight line—going from flower to flower on a horizontally growing morning glory vine. After it had sipped from the last morning glory flower, it flew without hesitation to the pendant flower of a Heleconia mariae. It drank, and then shot back into the rainforest. The hummingbird never hesitated in its foraging path to hover and search as it undoubtedly would have if it had been in a strange environment. It was flying along a familiar route which ornithologists call a “trapline.” Hermit hummingbirds tend to be “trapliners,” whereas the other hummingbirds tend to defend feeding territories concentrated around rich floral sources. The magnificent hummingbird does both. It has been known to trapline in parts of its range—in Colima, Mexico, for example—but defend feeding territories in other parts of its range, such as Oaxaca, Mexico.

Hummingbirds defend their feeding territories with a variety of displays. These can be vocal—calls and songs—or visual. They chase intruders with loud, species-specific chattering sounds. They mostly defend against other hummers encroaching upon their food resources, but any creature intruding upon their bush or tree might get dive-bombed. Gram-for-gram, male hummers must be the most ferocious birds on the face of the planet.

I watched blue-throated hummingbirds (Lampornis clemenciae) in the Oaxaca mountains utter their simple “wheep” songs while surveying their kingdoms from perches. These are uttered at rates of two or three per second. While foraging, the vocal signals are supplemented with spreading and flicking tails which function as visual threats.

Some hummingbirds have very complex songs. The late amateur ornithologist and author Crawford Greenewalt has described the song of the wedge-billed hummingbird (Schistes geoffroyi), which he said is as aesthetically pleasing to the human ear as the song of some songbirds. And renowned neotropical ornithologist Alexander Skutch has lauded the “sweetly varied outpouring” of the wine-throated hummingbird (Atthis ellioti) of Guatemala, no doubt his favorite hummingbird songster.

The song of the Anna’s hummingbird (Calypte anna) is not particularly pleasing to the human ear. It consists of series of buzzes (vibrati) and squeaks: buzz-buzz-buzz! buzz-buzz-buzz! squeak-squeak! buzz- buzz-buzz! However, recordings of Anna’s songs subjected to spectrographic analyses by Joe Marshall of the Smithsonian Institution and myself revealed that this is a very complex song indeed. I also found that different populations sang distinctly different song types, or regional dialects.

Humans produce sound with an organ called a larynx located at the apex of the trachea—the Adam’s apple. Birds produce vocal sounds with an instrument called a syrinx (plural, syringes)—Greek for “double flute”—located just after the windpipe divides into the two bronchial tubes. Birds thus have two sound-producing organs, one located on each bronchus. Both may be used to produce the same sound, or each syrinx may sing a different tune. This is dramatically illustrated when, for example, a starling calls like a gull and a fantail at exactly the same time. The two unrelated sounds can be seen clearly on a sound spectrogram (see Pacific Discovery, Spring 1999). My detailed examination of Anna’s hummingbird songs indicates that they too may sometimes sing two different songs simultaneously. In other words, an Anna’s may sing a duet with itself.

Songbirds, or oscines, have elaborately constructed syringes operated in part by four or more pairs of intrinsic muscles. However, hummingbirds have only two pairs of intrinsic muscles in their syrinx. It has long been dogma that the more complex syrinx of the oscine, in part, endows it with the ability to learn complex sounds. “Lower birds” with simpler syringes, such as hummingbirds, were thought to sing their songs by instinct.

Work with hand-reared birds as well as observations from the wild now indicate that hummingbirds learn, rather than inherit, their songs. The songs of adults normally consist of whistles, buzzes, and trills sung in specific sequences (syntax) or frequencies (approximately equivalent to pitch) at set rhythms. A male Anna’s hummingbird I hand-raised and kept away from adults of its species as it matured, produced a very abnormal song consisting almost entirely of squeaky whistles with no particular rhythm.

Three Anna’s hummingbirds hand-raised together produced similar songs as adults—that is, they learned from each other. These experiments demonstrate that the regional dialects of Anna’s hummingbirds are learned during an early period in their life, and that having complex syringes is not a prerequisite to learning complex songs after all.

In the late 1970s, Edward Mirsky, a UCLA doctoral student, recorded songs of a population of Anna’s hummingbirds on the Mexican island of Guadalupe. Sound spectrograms revealed that the songs of the island’s birds were drastically different from those of mainland individuals. When I compared sound spectrograms from my hand-raised bird with those recorded on Guadalupe, I was astounded to see how similar they were. It may very well be that the first Anna’s hummingbird to colonize Guadalupe had not yet completed its singing lessons, and sang a hummingbird version of “baby talk” which it passed on as an adult to its son and subsequent generations.

Not all sounds produced by hummingbirds are vocal. Some species, such as the broad-tailed hummingbird (Selasphorus platycercus) have notches on their wing feathers that produce a whistling sound as the birds patrol their territories. Ornithologists Sarah Miller and David Inouye of the University of Maryland found that if the notches in the broadtail’s wing feathers were blocked off with special glue, no sounds emanated during flight and these birds lost their territories. When the glue was removed, the wing whistles returned and the hummingbirds regained their domains.

Another group of birds that produces sounds with specialized feathers are the snipes. All snipe species have narrow outer tail feathers which produce a humming or whistling sound during their courtship flights. When these pecialized feathers are removed, pasted on a champagne cork, put on a string, and spun in the air, the same whistles can be heard.

The Costa’s hummingbird (Calypte costae) and Anna’s hummingbird of California have very elaborate dive displays during which whistles (Costa’s) or loud pops (Anna’s) are produced. It was long thought that these sounds were produced by the specialized tail feathers, as they are in the wing feathers of the broad-tailed.

During spring 1977, my ornithology class and I watched a Costa’s hummingbird perform its dive display in the Anza Borrego Desert of California. At the bottom of its dive we heard a long, drawn-out, high-pitched whistling sound. I informed my students that this sound was produced with the tail. At this point, the Costa’s perched not three meters from us, and out of his mouth emanated a shorter version of the same high-pitched whistle. He clearly had not read the literature; he wasn’t supposed to do that! I then compared spectrograms of dive-pops of the related Anna’s hummingbird and found that one of the syllables in the song was almost identical in structure to its “dive-pop” sound. Since then, three independent observers have reported to me their observations of Anna’s hummingbirds resting on perches and uttering dive-pop sounds. The dive sounds were vocal after all, and not mechanically produced.

It would be irresponsible to generalize from these two species and go on to say that all dive noises are vocal. I believe that each species of hummingbird must be studied on a case-by-case basis. Some species may utter vocalizations at the bottom of their dives, while others may produce mechanical sounds by specialized wing or tail feathers.

The aerial displays of hummers, once observed, will never be forgotten. The male Allen’s hummingbird performs one of the most elaborate. He flies back and forth over another hummingbird, tracing an invisible arc across the air some 20 to 30 feet across. At the end of each arc, he spreads his tail, and with his back toward the displayee, he shows off his rufous, black, and white patterning. Then he pauses in the air, shakes vigorously, and makes “chirruping” sounds similar to a cricket.

After a number of these arcs (I once counted as many as 23) the male climbs to a height of 75 to 100 feet. During the climb the hummingbird has his bill pointed skywards and his flight traces a spiraling or undulating path to the zenith. Without pausing, he then dives at a speed between 34 and 64 mph. At the bottom of the dive he suddenly veers up and makes a ripping sound: tup tup tup trrrrr! s

Dive displays in this species and most other hummingbirds studied are primarily aggressive in nature, and are directed at male or female hummingbirds of any species, or any intruder including mockingbirds (Mimus polyglottos), cats, and humans. The Allen’s has no song as such.

The Anna’s hummingbird hovers and sings during his aerial display. In contrast to the Allen’s, the Anna’s points his bill down during his climb and makes no pendulums preceding the ascent. As he ascends, he sometimes hovers and pauses to sing. Climbing up and up to as high as 75 to 100 feet, he pauses at the zenith, sings some more, then dives at great speed. He veers up at the bottom of the dive and produces a loud “pop” sound. His flight path traces a small loop as he comes out of the dive and hovers at the starting point of the display. The hummingbird usually faces the sun during the dive so that as he veers up at the bottom of the dive, sunlight catches his gorget feathers, which emit a flash of brilliant wine red.

With one possible exception, hummingbirds form no pair bonds. Males display and copulate with females, then females go off to build nests, lay eggs, and raise young all on their own. Males of most hermit hummingbirds and some tropical species gather in areas called “leks” where they perch and sing. Birds in each lek or even different parts of a lek may sing different song dialects. Colleague David Mullen and I studied a lek of green hermit hummers (Phaethornis guy) in Costa Rica in which males in different parts of the display arena sang three distinct song dialects. Anna’s hummingbirds are thought by some to display in “exploded leks”; that is, the males defend territories relatively far apart but within sight and sound of each other.

The female hummingbird builds a nest of mosses and plant fibers often bound together with spider webs. The outside of the nest is often decorated with pieces of lichen, and the nest cup is lined with insulating plant floss or animal hair. Occasionally, hummingbirds have been known to stack a new nest on top of a previous one.

Two eggs constitute a clutch, although on rare occasions Anna’s hummingbirds will lay three. The young hatch after an incubation period of about 14 to 17 days. Except for down feathers on the back, the newly hatched nestling is naked and blind and must be brooded by the mother. Feathers begin to develop after about six days. Nestlings fledge at 17 to 19 days and are still attended by the mother until old enough to feed themselves, and begin the cycle of song and display among a new generation.

Although much information has been garnered about hummingbirds, there is still much more to learn. The display and vocalizations of many species have not yet been described. Nests and eggs of some species have not yet been found. Feeding habits still need to be studied. With New World forests disappearing at an alarming rate, many species are in danger of losing their habitat and face extinction. It is a race against time to study each of these species of feathered gems before they disappear forever.

Luis Baptista, late Curator of Ornithology and Mammalogy at the California Academy of Sciences, is sorely missed by his colleagues, friends and family.