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Susan Tweit
Last updated on Saturday, December 21, 2002
Susan J. Tweit is a scientist who evolved into an award-winning writer and radio commentator. She is the author of five books for adults, including Barren, Wild, & Worthless: Living in the Chihuahuan Desert, personal stories about the history and natural history of Southern New Mexico, The Great Southwest Nature Factbook, a browser's guide to nature in the Southwest, from A to Z, and Seasons in the Desert: A Naturalist's Notebook, from Chronicle books. She has also written two children's books, Meet the Wild Southwest: Land of Hoodoos & Gila Monsters (Alaska Northwest Books) and City Foxes, a picture book which was named one of the Outstanding Science Books for Children for 1998.
Susan Tweit. Photo by Pamela Porter Her "Wild Lives" radio commentaries are heard three times weekly on KRWG-FM, Southern New Mexico public radio, and her columns run in the Las Cruces Sun News. Susan's essays and stories have appeared in Harrowsmith Country Life, New Mexico, Sierra, Cricket, Bloomsbury Review, and other magazines. She is the co-founder of Las Cruces' wildly popular - and fun - Border Book Festival. She is currently living in Colorado with her husband, Richard Cabe, and dog, Perdida Imelda.
Susan is a popular public speaker and leader of workshops. Her stories of our natural and human history have captivated a wide variety of audiences, including school classes, workshops, banquets, and professional meetings. As Bloomsbury Review put it, she brings the precision of a scientist and the passion of a poet, and is able to refocus readers' vision and ignite their imaginations.
Look for Susan's forthcoming book, Seasons on the Pacific Coast, due out from Chronicle Books in 1999. She is currently writing a memoir, Navigating by the Stars. Susan has a new web site! She invites you to come visit. Her books are available there, at local bookstores, or on-line through BarnesandNoble.com and Amazon.com (search by author for Susan Tweit).
Articles by Susan Tweit
Agaves, characteristic of New Mexico's Chihuahuan Desert and grasslands, live surprising lives. Agaves spend their first 5 to 35 years quietly growing a clump of long, stiff and leathery leaves in which they store food and water. But once mature, these succulent relatives of lilies squander all on one glorious-but terminal-burst of reproduction. A flower stalk spurts from the center of the leaf rosette, growing as fast as a foot a day and up to 15 feet tall. As the stalk grows, it draws its energy and water from the now-withering leaves. Soon dozens of buds swell along the stalk, and eventually open at night into big, tubular flowers that emit strong, musky fragrances, attracting bats, insects and other pollinators. By the time the flowers have matured into seeds, the agave plant itself is gray, shriveled, dead. Roadrunners' speed and agility allows them to catch venomous tarantulas, scorpions and centipedes without harming themselves; they also eat insects, lizards, small birds, cactus fruit and seeds. They rarely fly, instead sprinting as fast as 15 miles per hour across the desert. The roadrunner that I watch often catches lizards in our garden, snatching them and, since it lacks teeth, swallowing them whole. What doesn't fit hangs out of its mouth (like a child eating spaghetti!), the excess swallowed as the first digests. It also plucks dog food from a dish in the neighbor's yard. One searingly hot summer afternoon, I spotted a thrasher standing quite still on the ground in the shade of a small tree. The thrasher's long curved bill was open and its wings slightly spread. At first I thought that it was sick. But then I noticed a plump white-winged dove perched on a branch overhead. It too held its mouth wide open; as I watched, I could see the skin of its throat pulsating rapidly. Centipedes are arthropods - critters with external, jointed skeletons like insects, or shrimp, and belong to their own class, Chilopoda, Greek for "thousand feet." Actually, centipedes rarely have more than 60 or 70 feet, and the same number of legs. Although often called insects, centipedes possess too many legs: Insects have six or fewer; centipedes never fewer than 30. Also, insect bodies are divided into three very different segments; centipede bodies are comprised of a tiny head and many similar segments, each sporting one pair of legs. When Chihuahua chub were first collected in 1851, the notes accompanying the fish mistakenly recorded the collection location as "Rio Mimbres, tributary of the Gila," so the little fish were given the genus name Gila, commemorating the Gila River. However, the Mimbres is not a tributary of the Gila, nor are Chihuahua chub found in the Gila River. So much for scientific accuracy! The landscape of Southern New Mexico, West Texas, and northern Mexico has not always looked like it does today. In fact, beginning some 45 million years ago, parts of the region literally exploded, dramatically altering the shape of things. Time after time, volcanoes in the area erupted, spewing forth immense quantities of thick lava and clouds of boulder-to-dust-sized rock fragments. Torrential rains caused mudflows of volcanic debris to surge off the hillsides, drowning valleys and basins in mucky layers of debris. Lava oozed into horizontal and vertical cracks in the older layers, doming up whole areas, forming peaks, and hardening in rooster-comb-like dikes. It is hard to find a cottonwood in the desert nowadays. Where tall cottonwood overstories once marked the high-water lines of desert rivers and traced the sputtering lines of streams and springs, only an occasional twisted survivor remains. The disappearance of the cottonwoods and the associated bosques, Spanish for "woodlands," and cienegas, "marshes," resulted from several causes. Woodland clearcutting and livestock overgrazing in the late 1800s denuded whole watersheds, stripping the plant cover so that rainwater roared off, carrying the precious soil and causing once-permanent streams to alternate between brown floods and dusty drought. Steep-walled arroyos now gouge the landscape where streams and rivers once meandered, lined by cottonwoods and bosques. Dams controlled river flooding, but without the scouring action and rich sediment deposited by high water, cottonwoods could not reproduce. Farmers cleared the bosques and cottonwood overstory to create fields in the fertile soils of the river floodplains. The last hundred-fifty years have been tough ones for many of the West's wild creatures: the flood tide of humans, with our appetite for space and resources, has pushed out many, from bison to tiny desert fish. We have been hardest on predators - bears, wolves, coyotes, cougars, eagles, hawks - branding them "dangerous," slaughtering them by the millions. Many have disappeared or retreated to protected places. But not wily coyotes - they thrive. And, as urban and city habitat spreads, coyotes are moving in next door, their lively voices echoing through town. From several miles away, we spotted great swirls of cranes in the air over the fields. As we neared his house, we could see hundreds of the gray, long-necked and long-legged birds picking their way through the straw-colored stubble. When we stopped and rolled down the car windows, the wind brought us the purring murmur of thousands of sandhill voices. Cranes probed the soil for insects and seeds with spearlike beaks, cranes jumped and bowed on long, graceful legs, cranes preened iron-gray feathers, cranes took to the air on wide wings as we drove slowly along the fields. After an hour of careful counting we estimated that we'd seen at least 4,000 sandhill cranes. What an unexpected surprise! Creosote bush's distinctive odor and the leaves' shiny appearance are due to a resinous, varnish-like coating which helps the plant keep from drying out. The sophisticated coating also screens the sun's harsh rays, sheltering the delicate inner cells from heat and ultraviolet light. And it discourages grazers - the mix of waxes, volatile oils and other compounds tastes terrible and is indigestible to most animals. Only one small grasshopper, which spends its entire life on creosote, happily munches the resinous leaves. Dust devils certainly seem like magic, springing up suddenly from the hot ground, taking pale form from the soil they carry, and dancing whichever way they will. Creatures of warm climates and dry country, dust devils are children of the sun. Gila monsters and their cousins, Mexican beaded lizards, are the only two venomous lizards in the world. These "monstruos" - monsters, in Spanish - rely on a very simple venom-dispensing method. They bite their victim and hold fast; glands under the skin in their lower jaw secrete venom, which drips into the wound. Gila monster venom can kill small animals. In humans, the venom is severely painful, and causes swelling, nausea, and weakness, but it is not fatal. Despite their size, great horned owls are often overlooked because of their camouflaging feather pattern and their ability to fly without making a sound. The forward edge of their flight feathers is serrated to disrupt the flow of air over the wing, thus eliminating the noise created by airflow over a smooth surface. Rocky Mountain grizzlies are solitary except during mating season. They mate in June and July, hibernate from October until April, and only bear cubs every other year or every several years. In a warmer climate, with food available more of the year, did our southern plains grizzlies mate earlier? Hibernate for fewer months? Move into the desert during the rainy season to dig for flowering bulbs and roots? Were they truly more aggressive than the Rocky Mountain silvertips? We cannot know: except for the stories, and the long-clawed footprints chipped into the rock, they are gone. Kangaroo rats are not rats at all; nor are they kangaroos. These rodents are so named because they look like tiny kangaroos, with an upright, hopping gait, huge hind legs and feet, and a long, furry tail which comprises nearly two-thirds of their foot-or-so total length. While jogging down the irrigation ditchbank one afternoon, I heard a loud, rattling call. A not-quite-crow-sized bird flew up from a perch above the ditch with strong, precise wingbeats, headed downstream. Its distinctive silhouette included a daggerlike bill and a ragged crest atop a big head. Its plumage was sober blue above and pure white below. A wide blue-gray stripe crossed its chest. Kit foxes are almost exclusively nocturnal, and thus rarely seen. These smallest of North American foxes are beautifully adapted to life in the desert. Their pale coloring makes them nearly invisible against a background of light-colored desert soils. Thickly-furred paws allow them to trot silently as they go about their nightly rounds; the hair also helps them float on sandy soils. Large ears help these dusk-to-dawn hunters to pick up night sounds. Even their small size may work to their advantage, making it easier to keep cool. In 1959, the Smithsonian Institution Annual Report carried the story of strange mirages seen near Yuma, Arizona. On hot, unusually still days, a clear image of a city appeared in the desert to the west of Yuma. It was no phantom either - the shimmering image was unmistakably that of San Diego, California, 150 miles west on the Pacific Coast, beyond several mountain ranges. Mistletoe, the plant made into Christmas "kissing balls," is one of the few truly parasitic flowering plants. Instead of producing its own food, mistletoe feeds on trees. When a sticky mistletoe seed sprouts on a tree branch, it sends a root into the tree's veins, and draws its food and water from the tree. Mistletoe grows into a dense mass of many-branched stems, well-described by its Navajo name, "basket on high." Eventually, however, a mistletoe may be doomed by its own success: dense mistletoe growth may kill its tree host. Male mockingbirds exercise their vocal artistry most during the early spring and summer mating seasons. They sing for reasons similar to those which motivate human males to cruise city streets: to advertise their maleness, attract mates, discourage competitors, and to delineate their territories. The more extensive his vocal repertoire, the better chance a male mockingbird has of mimicking and driving away other birds, thereby gaining a larger share of habitat, and more access to the female listening audience. The songsters pick high perches - television antennas, utility poles, or tall cacti, shrubs, or trees - to better broadcast their signals. Unmated males sometimes sing all night long! Mountain lions, also called cougars, pumas, or simply leones, are the second largest cat in the Americas. (Only jaguars are larger.) Full-grown male leones weigh around 160 pounds (females weigh in at about 135 pounds), and measure up to seven feet from nose to the end of their long tail. These big cats were once the most widespread wild cat in the Americas, ranging from Patagonia to Canada, and from the Pacific Coast to the Atlantic. These days, mountain lions are much less common, but lion populations are still healthy in New Mexico because of the rugged terrain and abundant habitat.People often ask me why I am a nature writer. After much thought, I know what to say: The stories of our wild relatives - the plants, the animals, the desert itself - are the most important stories that I know.
Like any landscape, the Chihuahuan Desert abounds with lives, with wild neighbors that we often don't notice or don't know. Take the spadefoot toad, a tiny amphibian that appears as if by magic after summer thunderstorms, filling the night with its mating calls, and then vanishing just as quickly when the ephemeral rainwater is gone. Or the shabby-looking creosote bush that by coating itself with a sophisticated protective armor comprised of dozens of smelly and bad-tasting compounds, also produces the desert's signature fragrance.
One evening in early May, I set out on a walk along the irrigation ditch at dusk. As I turned the corner onto the ditch road, I saw a cloud of birds flying back and forth, skimming low over the water, fluttering up over the road, then turning and flying back down the ditch like swimmers executing graceful laps. Pack rats are particularly attracted to shiny objects - watches, jewelry, coins, and, of course, aluminum cans. One nest even sported an upper denture plate! An average den of a desert-dwelling pack rat contains about 20 cubic feet of material - enough to fill a trash bag‹and may reach 4.5 feet high by 2 feet wide. Piñacate beetles are among the most conspicuous insects in the Southwest. Over a hundred species live from lowland deserts to foothills to piñon-juniper woodlands. Feeding on minute particles of wind-blown organic matter and fungus, Piñacate beetles help recycle nutrients and keep arid-country soils fertile. On these hot, dry June days when the horizon shimmers, set to dancing by the waves of heat that rise from the ground, I think of beaches. Not ocean beaches - playas -desert beaches. Playas are the dry, incredibly level beds of ancient lakes. Found in desert country throughout the southern Southwest and northern Mexico, and the Great Basin country of western Utah and Nevada, normally-dry playas occasionally fill with a skim of water - sometimes no more than inches deep over many square miles - after a heavy summer rain or spring snowmelt. Such lakes never last more than days or weeks, soon evaporating to leave behind huge expanses of mudflats drying in the sun. Playas were named by Spanish explorers for their resemblance to beaches - very flat beaches. Prairie dogs are colonial critters, living in extensive colonies of hundreds to millions of individual animals. Each prairie dog colony is divided into half-acre neighborhoods called coteries, inhabited by one male, several females, and the young of the year. Coterie members greet each other by "kissing," gently touching noses and lips. Quail are among the desert's most beloved birds. Gregarious and loquacious, they live in groups and fill the air with their soft whistles, clucks and metallic plinking sounds. Their habits make quail easily seen and heard. In The Mysterious Lands, Ann Zwinger describes Gambel's quail: "They remind me of charming wind-up toys - bustling about with staccato movements, officiously giving each other directions as they forage among the creosote bushes. In winter, quail often congregate in flocks of one or two hundred birds; in summer, they split up into family-group coveys of a dozen or so. They graze the desert like flocks of small chickens, munching on succulent plants, fruits and seeds, and insects." Rattlesnakes come equipped with a venom-dispensing mechanism that is among the most sophisticated of all snakes'. Hollow fangs folded back at the front of their upper jaw swing down and forward when a rattler bites, stabbing and dripping venom in a single swift thrust. Rattlers' neurotoxic venom serves to subdue their prey, and also as self-defense. Rattlesnakes hunt and eat a wide variety of prey, mostly rodents such as mice and kangaroo rats, but also other small mammals, birds, lizards, and frogs. Their broad, triangular heads are designed to accommodate articulated jaws which open many times as wide as human jaws, allowing rattlers to swallow prey as large as prairie dogs whole. Ravens gather as fall days become shorter, aggregating in larger and larger flocks until their winter roosts number a few hundred, or a thousand birds. Such a nighttime raven roost sounds like a city of restless sleepers: the air is alive with mutters, soft cries, whimpers, sighs. The black shapes shift and rustle, jockeying for better positions in the roost trees. Now and then a few ravens will suddenly rise into the air on stiff black wings, then one by one, drift back to settle on the branches again. Autumn slips across the desert quietly. Although nights grow chill, summer's heat lingers in the afternoons, and the greenery brought on by summer rains simply fades to dusty olive, bleached straw, and weathered brown. As the soil dries out, mesquites, desert willows, and ocotillo drop their leaves without any fanfare. But here and there where water flows - a spring, stream, an irrigation ditch, or a river - autumn shows in the rich yellows and golds of cottonwood trees. River otters are the Southwest's water acrobats. These graceful animals swim right side up, upside down, on their side, or any way they choose. River otters can undulate like fish, using their heavy tail as a rudder. They can execute sudden U-turns, dive as deep as 40 feet, and race one another. These playful animals make slides in muddy or icy streambanks by loping up the bank, flopping on their belly, then sliding with a "splash" into the water. River otters are gregarious animals, and are usually seen in pairs or family groups. Spadefoots spend much of their lives - years, in extreme droughts - dug deep under the soil surface, barely respiring, dormant. But after heavy summer rains, they emerge in noisy abundance. Roused by the sound waves of thunder, the toads tunnel upwards at night from solitary burrows as deep as two feet below the surface, hop to the nearest water - puddles, temporary ponds, roadside ditches - and squat, rehydrating their parched bodies through a porous skin patch on their bellies. Males float and bellow their desire; the curious trills and bleats of thousands of tiny swelling throats carry for miles. Females, drawn to the din, find a mate: The two float while he clambers atop her and squirts sperm over the eggs she exudes. Spadefoot toads are named for their "spades," black, sharp-edged scrapers on the underside of each hind leg near their hind foot. Like many desert residents, these small amphibians take refuge in the soil to escape both drought and extreme temperatures. Unlike most, however, spadefoots spend the majority of their lives - years, in extreme droughts - dug deep in the earth, barely respiring, dormant. Since spadefoots literally dehydrate when exposed to dry air, they emerge only on a handful of nights each year when water is briefly abundant during the summer monsoon season. Their sudden appearance and equally abrupt disappearance raises many questions. For instance, what do they eat? "As we toiled across these sterile plains, where no tree offered its friendly shade, the sun glowing fiercely, and the wind hot from the parched earth - the thought would keep suggesting itself, Is this the land which we have purchased, and are to survey and keep at such a cost? As far as the eye can reach stretches one unbroken waste, barren, wild, and worthless." From the side, a razorback sucker looks quite bizarre, with its blunt-nosed head and high, humped back. But the fish is perfectly adapted for the habitat where it lives out its adult years: the turbulent reaches of desert rivers. Its flattened body and knife-thin back hump act as a keel, helping the fish easily stay oriented in roaring currents. That tiny mouth with its thick lips vacuums up small bits of food mainly fly and mosquito larvae, and algae‹from riverbottom rocks. A small hump-backed mountain rises above East Mesa, midway between Las Cruces and the Organ Mountains. It is often called "A" Mountain for the Aggies "A" blazed on its west side like a gargantuan modern pictograph. But I prefer its older name, Tortugas, or "Tortoise" Mountain, for its resemblance - when viewed from the south - to a huge tortoise slowly ascending the bajada. A symbol of the West in movies and popular songs, tumbleweed is actually not native here at all. As Russian-thistle, its other common name, suggests, tumbleweed comes from Russia's arid shrub steppes, half a world away. After hitching a ride to America in the 1870s with flax seed brought by Ukrainian farmers, tumbleweed spread like wildfire across disturbed places in the West, colonizing plowed prairies, overgrazed rangelands, road edges, corrals, and the bare earth of abandoned farms. No wonder that one Hopi name for tumbleweed is "white man's plant." By the time the Sons of the Pioneers recorded "Tumbling Tumbleweeds" in 1934, this invader had come to symbolize the rootless, restless Western culture. Whip scorpions, or vinegarones, are related to both spiders and scorpions. But unlike the latter and some of the former, they are not venomous, although they look quite formidable. Their 3.5-inch-long, blackish body resembles an overgrown scorpion, with stout, inward-curving pincers as long as my thumb extending forward from their tiny head. Four pairs of slender legs stretch from their many-segmented abdomen; the first pair function as antennae, sweeping the ground in front of the whip scorpion, like a blind person feeling their way with a white cane. (Not that whip scorpions are blind; on the contrary, they possess eight perfectly serviceable compound eyes - two just above the mouth between the massive pincers, three on each side of their head. But they hunt in the dark, capturing their prey by feel.) Ungainly on land, vultures excel in the air. These master gliders can soar gracefully for hours with nary a beat of their 6-foot-wide wings, riding thermals - rising columns or bubbles of warm air - or coasting on the streams of wind. With broad wings and a low wing loading (the ratio of body weight to wing area), vultures can soar at extremely slow speeds without sacrificing maneuverability. By soaring with their wingtip feathers spread wide like the fingers on a hand, vultures counteract the large amount of drag produced by their wide wings, reducing wingtip turbulence and lowering their stalling speed. When soaring slowly, vultures actually glide downward to maintain forward thrust, but they stay aloft because the rising warm air propels them upwards faster than they sink. One spring, we raised the cement block wall that encloses our yard. Soon after the builders had finished, I saw the first lizard of the year, stretched out in the sun on the vertical face of the wall as if gravity had no hold on her slight body. I borrowed Richard's binoculars for a closer view. Just about five inches long, the lagartija (little lizard) was faded brown all over, and marked head to tail with cream-colored stripes, each paralleled by a precise line of tiny, yellow dots. The lizard's hind legs were huge, and her tail extravagently long. Water is worthy of note here: deserts are by nature dry. Our part of the Chihuahuan desert, once an arid grassland, now dominated by creosote bush, mesquites, and other shrubs, boasts an annual average precipitation of less than ten inches. Soaptree yucca is an interesting plant in all seasons. But its flowers are truly spectacular. In late spring and early summer, soaptree yucca sprouts flower stalks up to ten feet tall, laden with clusters of waxy, ivory-colored, bell-shaped blossoms. On moonlit nights, the tall, glowing columns inspire another common name: "Our Lord's Candles."
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