Читать книгу Nature Obscura - Kelly Brenner - Страница 8

Imagine, if you will, an animal that weighs the same as two dimes. This tiny creature has a heart that beats up to 1,250 times a minute when active. At rest, it takes 250 breaths a minute. Its tiny wings beat up to 200 times a second, which propels its flight to 30 miles per hour and hits 60 on a dive. This bird must consume at least double its body weight each day, and feed frequently during the day, or starve to death within a matter of hours. The food this animal consumes is nectar, supplemented with insects. It’s hard not only to find the time to eat constantly, but to find enough to eat. Now imagine having to find enough insects and nectar in the dead of winter, not in sunny San Diego, but in Seattle. This is the story of Anna’s hummingbird.

Of the more than 320 species of hummingbird in the New World only 14 visit the United States. A mere four regularly make their way to Washington State and just two visit Seattle. But only a single species, the Anna’s hummingbird, can be found here throughout all the seasons. My yard is one of many that the Anna’s visit, and I watch them throughout the year. They are my constant companions—as long as I keep feeding them. If I forget to fill the feeders or go on vacation, they’ll abandon my house and visit one of the many others in the area that also provides feeders. I don’t take it personally.

I’ve fed and watched Anna’s hummingbirds for well over a decade, from a small balcony near Portland to the small front yard of a rental house in Eugene, Oregon. Even while we lived in the middle of the city in Seattle, they found my lavender plants up on the sixth-floor balcony and visited regularly. Today, at our house in south Seattle, I feed them in both my front and back yards.

Neither explorers Meriwether Lewis and William Clark in 1805 nor David Douglas in the 1820s ever encountered the Anna’s hummingbird. The birds didn’t live here when Washington became a state in 1889. They likewise missed out on the Alaska-Yukon-Pacific Exposition, the opening of the Smith Tower, the Spirit of St. Louis landing at Sand Point Naval Air Station, the collapse of the Tacoma Narrows Bridge, and the Seattle’s World’s Fair. Anna’s hummingbirds were not documented in Seattle until 1965, and it wasn’t until Luke Skywalker blew up the Death Star to cheers of audiences in 1977 that they started nesting here. These little nomads are not just increasing their range, however; they’re also increasing in number. The population of Anna’s has risen sevenfold in the Seattle area since 1990. A bird that just started breeding here the year I was born (1978) is now commonplace in my yard.

It is thought that the Anna’s relatively sudden movement to Seattle is due in large part to an Australian tree, the eucalyptus. Along with tree tobacco, another non-native tree favored by hummingbirds, eucalyptus was introduced to Southern California somewhere around 1870 and quickly spread throughout much of the state, providing an ideal hummingbird resource in places previously bereft of nectar-producing plants in winter. The hummingbirds then expanded northward from their historic chaparral habitat of dense thickets of tangled, thorny shrubs in Baja California and Southern California.

Simultaneously, humans moved into other areas historically devoid of nectar flowers and began dramatically altering those habitats by planting gardens filled with exotic, nectar-producing plants. Landscapes that had been previously unsuitable for hummingbirds were now capable of sustaining them, and thus began a historic change in Anna’s distribution. From California they moved steadily northward, following the landscape of flower-rich urban and suburban gardens into Oregon and shortly after into Washington. Although not yet directly studied, it’s currently believed Anna’s are entirely dependent on the feeders humans put out, along with the exotic flowering plants in this part of their current range. They rarely venture far from human settlements, living alongside us all year round.

But who was Anna? The first official specimen of this little bird resided in the collection of one François Victor Masséna, the Duke of Rivoli. It was acquired courtesy of Paolo Emilio Botta, who collected it in San Francisco during his voyage aboard Le Héros beginning in 1826. Later, naturalist René-Primevère Lesson found the specimen in the Masséna collection while researching his book on hummingbirds and determined that it was a previously unknown species. He was the first to describe the new species and bestowed the name of Calypte anna, Anna’s hummingbird, in honor of Masséna’s wife, Anna de Belle Masséna.

By all accounts the Duchess of Rivoli was a beautiful woman. John James Audubon himself was taken with her grace and beauty. And yet it’s perhaps ironic that this beautiful hummingbird was named for a beautiful woman because the female Anna’s hummingbird is a rather dull bird; it’s the male that has the resplendent ruby-red head.

Male Anna’s hummingbirds rarely go unnoticed in our yard because they have evolved elaborate head decorations to attract the attention of females. A male Anna’s head is completely covered in bright, shimmering, gemstone-like feathers as if he’s wearing a shining helmet, and in fact Calypte is believed to derive from a Greek word meaning just that. Still, you’d be hard-pressed to find a helmet in any museum so extravagantly colored.

Having studied the male that frequently perches on the feeder by my office window, I think it looks more like he is wearing a Mardi Gras mask. That’s because he has what’s called a gorget, named after the piece of medieval armor that protected the throat. Along the sides of his neck I’ve noticed the feathers sticking out on either side, so that, viewed from behind, it looks as if he has little wings on his neck.

I can often tell when a female is near because the male will raise the feathers on the top of his head as well, adding to the Mardi Gras effect. Just to make absolutely sure the female doesn’t miss him, the male will move his head back and forth to catch the light on his iridescent feathers and then sing a complex song full of scratching chirps and squeaks.

To us the female Anna’s may appear more homely, and when one visits my feeder I have to look closely to see her greatest extravagance: a trace of metallic red streaks on her throat. The dull colors greatly benefit the female Anna’s, who do their best to live their lives unnoticed. When females feed on nectar from flowers, their green backs blend in with the foliage; and when they sit on their eggs, the eggs are camouflaged by the birds’ green feathers.

From my dining room window I watch the tiny hummingbird hover over the red feeder hanging from a suction cup on the window. It is an adult male, and before long he dives down to take a drink of nectar, or more specifically sugar water—four parts water to one part sugar—that I’ve brewed on the stove. Before I went to bed, I took the feeder down and brought it inside so the sugar water wouldn’t freeze when the temperature dropped that night. In the morning I put it back out as soon as I was up, and he was already waiting for me, arriving before I had the window closed. In winter I see hummingbirds at the feeders almost constantly. I often dine with them—myself at the dining table with a cup of steaming hot tea and a stack of chocolate chip pancakes, and the birds at the window feeder a few feet away drinking cold sugar water.

It seems unfair that I’m so warm and comfortable inside as they fly around over the frosty grass and frozen birdbaths. Hummingbirds have to visit the feeders frequently because they’re at the extreme end of the vertebrate scale; they’re the smallest an animal can be. If the hummingbird’s minuscule body, no more than four inches long, was any smaller, it simply couldn’t eat enough to survive. Its tiny heart, the largest of all warm-blooded animals relative to body size, powers its flight. The pectoral muscles of a hummingbird, those responsible for flight, make up an astonishing 25 to 30 percent of the bird’s entire body weight.

Hummingbirds use up more energy than any other animal relative to body size. To create that much energy, they must consume double their body weight in food and water each day, a task I help with by putting out feeders in winter and planting hummingbird-friendly flowers—those that are often red in color and tubular in shape—for spring and summer blooms. In my yard they frequently visit the orange honeysuckle, twinberry, red columbine, fireweed, and lupine. Hummingbirds are strongly attracted to the color red and are known to closely investigate people wearing red. The nectar, both human-made and natural, provides an energy-rich food source for them.

Sometimes I watch them in the trees, buzzing around as though looking for something—and in fact they are. They use their keen eyesight to find tiny insects hidden on branches, in the bark, or under leaves. These protein-rich morsels supplement their diet and help provide a food source when nectar is scarce. Hummingbirds are also known to follow sapsuckers to consume the tree sap collected in wells drilled by the birds, as well as the insects stuck in the sap. In addition to nectar and insects, they must drink up to eight times their own weight in water each day.

Without watching for him, I heard a slight chirp and knew that he was back. My eyes caught a flash of red and a blur of wings as the bird zipped up to within a couple inches of my face, a pane of glass separating us. He quickly surveyed for danger, looking at me with tiny eyes. I held myself motionless, and he seemed content flitting down to the feeder I’d attached to the window. He deftly dipped his needlelike bill into the small red metal flower before quickly hovering backward to peer at me again. Now he seemed more comfortable as he moved back to the flower, and this time he landed, grasping the edge of the feeder with minuscule feet—feet that are unable to walk, only sidle along a branch or feeder. The tiny green bird with the red head fed more leisurely, and yet even at leisure he moved unnaturally fast. All his body movements were jerky, even the gulping of his throat seemed quick, almost desperate. The tongue of the Anna’s is split at the end like that of a snake; the two halves each contain compressed tubes, but once the tips reach the nectar, the tubes open, drawing the fluid in. This male eventually removed his long bill from the flower, looked around, uttered a high squeak at seeing a competitor, and flew off after it faster than my eyes could follow.

Adult birds are much larger than I’d expect given their weight. When it’s cold outside, I’ve regularly noticed these fluffy little ping-pong balls perching in our tree branches. Though they lack the downy layer that many other birds possess, they puff up their feathers to act as insulation, keeping pockets of warm air inside, while the outer feathers act as a barrier, keeping out rain, snow, and the cold.

Feathers alone aren’t enough to survive the cold nights, so the birds build up their body weight during the day by constantly feeding, and they fill up their crops—a pouch many birds have and use for temporarily storing extra food—before it gets dark. The stored food, both as fat and nectar from the crop, is slowly digested at night; hummingbirds make it last. On cold nights hummingbirds can enter a state of torpor, which is somewhere between sleeping and hibernation. While in torpor their body temperature goes down to about 55 degrees and their heart rate drops to 50 beats per minute—in stark contrast to their usual 250 beats per minute at rest. To further help them survive the cold, they may roost next to porch lights or chimneys, human-made places that emit warmth during the night.

In winter the female birds coming to my feeders may very well be carrying eggs, although to my eyes they look the same as always. Anna’s eggs are about the size of peas and are usually laid in pairs. Tiny, but taking the female’s body size into account, they can be as much as 12 percent of her weight when they’re laid. As a comparison, my daughter was less than 5 percent of my body weight when she was born. In Seattle, Anna’s nest as early as February, a full month before our other breeding hummingbird, the rufous, even arrives. While the rufous is migrating hundreds of miles north from Mexico, our Anna’s are busy incubating their eggs, sometimes while covered in snow, or being pelted with rain or wind. For up to three weeks they suffer through this, alone.

Anna’s are single mothers—they build the nest, lay eggs, incubate, and feed their chicks each on their own. The nest is no larger than a golf ball and is very hard to find, despite being commonly located in backyards and parks. While the inside is lined with fluffy seeds and downy feathers, the outside is covered in camouflaging lichens and moss, the entire thing bound together with webs stolen from spiders. This tiny nest is masterfully constructed to be hidden and very warm. One study found that hummingbird nests have a thermal conductivity on par with that of polar bear fur.

Chicks hatch blind with pink, naked bodies and underdeveloped bills. The mother feeds them by poking her long bill down the chicks’ stubby bills and regurgitating nectar. The chicks have relatively well-developed crops, which are disproportionately large and can bulge out of their necks impressively when full of regurgitated food. The naked, fattening chicks are utterly defenseless against weather and predators.

A mother grizzly has nothing on a mother Anna’s when she’s defending her nest. Females have been seen driving off and buzzing at birds many times their own size, including jays, crows, and hawks. Even humans considered to be a threat have been harassed by tenacious hummingbirds. It’s for good reason: nests suffer a high mortality rate, and jays and crows are guilty of picking chicks from nests. The mother herself is not always safe, and while she is feeding on nectar she is at risk from outdoor cats. The one thing she can’t do much about is the weather; storms and frosts can increase the mortality of adult and chicks alike.

There are rarely two hummingbirds at either of my feeders at the same time. The male that visits my feeder in the front yard does not tolerate any other hummingbirds. He keeps a close eye on any movement around his territory, and I often see him leap up from the feeder and speed off in pursuit. The rest of the time he’s sitting in a small tree nearby watching for intruders or potential mates. I frequently hear a series of squeaky chirps while sitting at my desk, and I know without even looking that there’s yet another hummingbird dispute right outside the window. And although I haven’t witnessed an actual fight, the tussles can and do get physical. Usually the disputes are settled by chases or dive displays.

Late one winter I was in the yard checking for signs of life in my plants. While looking at the gooseberry buds I heard a high-pitched, loud chirp. I looked straight up, very high in the sky, and saw a speck, so small that it may have been a spot in my vision from looking at the bright sky. But then it moved impossibly fast, straight down toward the apple tree on the other side of the fence. I heard the loud chirp again and finally made out the tiny figure of a hummingbird. It flew in an arc back up to just above the tree and stopped briefly to utter its chittering song; then it flew up like a rocket to start the routine again. Instead of watching the male, I turned my eyes to the bare branches of the tree because I knew a female was likely perched there. The male dove to impress her, hopefully enough to encourage her to mate. Sometimes the male uses it to deter competitors, but usually he saves the display for females.

The male may have impressive aerial skills and a fancy appearance, but since I began watching and being involved in the lives of my visitors, I have developed a great deal of respect for the ferocity and endurance of the single mothers. Without my realizing it, over time, the lives of these birds right outside my windows have become woven into my own as we both go about our daily routines together, separated by a pane of glass.