Tornado Alley

North America is the tornado capital of the world and the majority of these twisters occur in the Southeastern and Central U.S. Tornadoes may occur during any month of the year but their numbers peak from March through June.

The largest and most powerful tornadoes tend to develop in a broad swath from central Texas to Nebraska, a zone dubbed "Tornado Alley." This region is prone to the formation of super cell thunderstorms: giant, rotating storms with cloudtops near 50,000 feet. These super cells usually form along the "dry line," which trails southward from the front's zone of low pressure. At this line, dry air from the west clashes with warm, moist air from the Gulf of Mexico; just east of the line, the dry air temporarily overrides and caps the muggy air at the surface. Eventually, this cap breaks down and the warm, unstable air rushes into the cold, upper atmosphere, where the jet stream injects more energy and triggers rotation: a super cell is born.

Moving northeastward in advance of the front, these massive storms often spawn tornadoes at their trailing, southwestern edge. Like hurricanes, super cell thunderstorms feed on the warm, moist air that flows up through their center; should they encounter rain-cooled air left behind by other storms, they begin to dissipate. For that reason, the loner storms tend to be more powerful and more dangerous; storm chasers know that these solitary monsters provide the best opportunity for close encounters with twisters.

Bean Trees

The redbuds are blooming in Columbia. These small trees, festooned with pink-purple flowers, are used as ornamentals throughout the eastern U.S. In the wild, redbuds are understory trees and are generally found along wood margins, in glades and on rocky hillsides.

Redbuds are a member of the legume family which includes many herbs (lupine, bluebonnets, clover), vines (wisteria, kudzu), crops (alfalfa, peas, beans, peanuts), shrubs and trees. Most of the legumes have nitrogen fixing bacteria in their root system, which help to enrich the soil, and nearly all produce elongated seed pods. The numerous seed pods of the redbud can be a nuisance for the homeowner and often produce weed-like seedlings in every nearby flowerbed.

Other legume trees include the acacias, mesquite and paloverde trees of the desert Southwest, Kentucky coffeetrees, mimosa, black locusts and honeylocusts. Most of these trees are drought tolerant and the latter two grow especially well on our farm in the semiarid climate of the Colorado Front Range.

Coming Ashore

Life evolved in the ocean 3.6 billion years ago but it would be another 3.2 billion years before plants and animals colonized the land. It was during the Silurian Period (440-400 million years ago) that the ozone layer had thickened sufficiently to permit life forms to leave the protective waters of the primordial sea; of course, these plants and animals had also developed features that allowed them to survive on land.

Vascular plants, equipped with stems, first appeared in the Silurian. Stems harbor tubules which permit the transport of water and nutrients throughout the plant, protecting it's various parts from dessication; this feature was vital to the evolution of land plants. The first species, of course, colonized the shoreline, relying on the tides for nourishment; over time, root systems became for efficient and the plants lost their dependence on the sea.

The first land animals are thought to have been millipede-like creatures which also inhabited the tidal zone. Initially amphibious, they eventually became terrestrial, following the advance of the plant-line. While these pioneers were invading the coast, ammonites (ancestors of squid, cuddlefish and octopi) and the first jawed vertebrates (placoderms) were appearing in the ocean. Sharks, boney fish and lungfish would not evolve until the next geologic period, the Devonian.

Trilling Toads

After a week of warm, rainy weather, the toads were calling last night. Their high-pitched, musical trills indicated that they were American toads, one of the more common amphibians in the eastern U.S. The males emerge from their winter burrows in late March or early April and soon gather at shallow ponds or temporary pools to breed; their song attracts the larger females, which lay up to 20,000 eggs in long, gelatinous strips. The eggs will hatch into small, black tadpoles within 10-12 days and these will morph into toadlets by June.

Recognized by their dry, warty skin and a large parotid gland behind each eye, the American toad favors rocky woodlands but is also common in Midwestern suburbs. Solitary creatures, toads are primarily nocturnal, spending the day under rocks, logs or shrubs. They are most often seen at dusk as they hunt for insects, slugs, worms and moths; since they feed on many destructive insects, they are a welcome resident in any garden.

The Rift Valley

The Rift Valley of East Africa is the southern end of a 4000 mile rift that begins in the Beqaa Valley of Lebanon and extends southward through the Jordan River Valley, the Dead Sea, the Gulf of Aqaba and the Red Sea. At the southern tip of the Red Sea, an eastern branch runs through the Gulf of Aden, extending to the mid-oceanic ridge of the Indian Ocean.

The African portion of this Great Rift, which began to develop 40 million years ago, is comprised of two parallel rift valleys which stretch from Ethiopia to Mozambique. The western channel harbors some of the larger lakes in Africa, including Lake Tanganyika, one of the deepest freshwater lakes in the world. The eastern rift is well known for its early hominid fossils (especially within the Olduvai Gorge) and is characterized by a chain of basin lakes; with no outlet to the sea, these shallow lakes flucutate throughout the year, leaving broad salt flats during the dry season.

As is true with other rift areas, volcanic features are common throughout the Rift Valley; the rifting process is often triggered by the development of mantle plumes and, as the crust is stretched and thinned, lava flows and volcanoes develop. Volcanic mountain chains rise along both channels of the African Rift but the most famous, Mt. Kenya and Mt. Kilimanjaro, developed along the eastern rift. The Ngorongoro Crater, known for its fabulous diversity of wildlife, is the remnant of a large volcano in the eastern rift of northern Tanzania; fourteen miles wide, it is one of the largest intact volcanic craters on Earth.

Over time, the Rift Valley of Africa will be invaded by the sea, just as happened in the Red Sea, the Gulf of Aden, the Gulf of California and numerous other rift zones across the globe; once this happens, the sub-Continent of East Africa will break from the motherland.

Man and his Lawn

The lawn, pride of the American homeowner, is not a natural landscape. Lawns are generally a blend of hybrid grasses and, unfortunately, are often maintained by the application of chemical fertilizers, herbicides and pesticides. They may be good for picnics, frisbee tossing and croquet, but they can be a detriment to the natural environment.

If you hope to attract a wide variety of wildlife to your property, try to minimize your lawn coverage. Expand wild borders with trees, berry-producing shrubs and native wildflowers. Leave grass clippings to fertilize the lawn and try to maintain its health with aeration and limited watering. Learning to accept dandelions, clover, plantain, wild violets and other "weeds" will make your landscape more colorful and more attractive to wildlife. Moles and birds will keep the grubs in check.

Of course, the lawn maintenance companies would scoff at this advice; then again, they're not in the conservation business.

Early Birds

In birding lingo, a summer resident is a bird that arrives in spring, breeds and departs in the fall for southern climes or lower elevations, escaping the harsh winter conditions. Most summer songbirds feed on insects or nectar and must leave before cold weather kills off their source of nourishment. In the Midwest, the majority of summer residents arrive in April, after the risk of a hard freeze has passed. Two exceptions are the eastern phoebe and tree swallow, which turn up during the latter half of March.

Tree swallows usually arrive in large flocks, gathering in bottomland woods along our lakes and rivers. Identified by their blue-green back, white underparts and slightly forked tail, these insectivores will soon pair off and look for a tree cavity in which to nest; some will use bluebird boxes or other man-made structures. Eastern phoebes, which look like miniature eastern kingbirds, take up residence along streams and wetlands, flycatching from saplings or from limbs that overhang the water. Both birds rely on the moderating effect that streams and lakes have on air temperature, allowing insects to remain active on cold March days.

From Teays to Ohio

During most of the Cenozoic Era, the Teays River and its tributaries drained a large area of the eastern U.S. Heading in the mountains of northwest North Carolina and southwest Virginia, this large river flowed northward through West Virginia, northwestward across Ohio and then westward across northern Indiana and Illinois before merging with the Upper Mississippi. As the Nebraskan and Kansan Glaciers plowed into the Midwest (2 million to 600,000 years ago), the channel of the Teays was blocked with ice and a large lake, comparable to Lake Erie in size, covered southern Ohio, northwestern West Virginia and northern Kentucky. Eventually, these lake waters spilled to the west-southwest, creating the Ohio River channel.

The New and Kanawha Rivers of West Virginia are remnants of the Teays, as is the Scioto Valley of southern Ohio; the Scioto River now flows southward through the old Teays valley. The upper Ohio River, east of the Kanawha junction, was formerly a tributary of the Teays. All remnants of the Teays Valley across western Ohio, northern Indiana and Illinois have since been buried by a thick layer of glacial till.

Hysteria in the Suburbs

As March blends with April, the hysterical call of the flicker greets the day. Not content with the sound of his own voice, this frenzied woodpecker hammers away at metal vents and downspouts, sending loud vibrations throughout the neighborhood.

Spurred on by hormones, such territorial displays are common at this time of year. The loud cries of the red-bellied woodpecker are also ringing through the suburbs and the drumming of downy, hairy and pileated woodpeckers echo across our woodlands. This is their mating season and female woodpeckers must love percussion.

Early Bloomers

The late winter and early spring flowers are the ones we appreciate the most. They bring the first splash of color to a bleak winter landscape and give us hope that the tide has turned toward longer, warmer days.

Snowdrops, winter aconites, scilia, hyacinths, periwinkle and crocuses are the first to appear, often by late February in Missouri. By mid March, clumps of daffodils brighten our yards, soon followed by the early tulips. Wild cherry and forsythia are among the earlier shrubs to bloom and, by mid-late March, red maples, hawthornes and deciduous magnolias paint the suburbs. Peach and apricot are usually the first fruit trees to flower, often losing their blossoms (and potential fruit) to the cold snaps of our fickle March weather.

The Hualapai Travesty

So the Hualapai Indian Tribe has dedicated their glass-bottomed walkway over the rim of the Grand Canyon, a marvel of engineering and a disgrace to mankind. It reminds me of the "frontier village" that Colorado sanctioned at the Royal Gorge Bridge. Many humans cannot seem to appreciate the majesty of nature until it becomes a source for the almighty dollar!

These "Native Americans," as it turns out, are not much different from the tycoons of Wall Street, some of whom likely backed the project. I suspect the walkway will soon become the centerpiece of a "Grand Canyon Wonderland," complete with tourist shops, fast food restaurants and roller coasters. Those who visit and support such blights on our landscape are hypocritical "nature lovers."

The Colorado Plateau

Harboring some of the most spectacular scenery on the planet, the Colorado Plateau stretches across western Colorado, northwestern New Mexico, northern Arizona and the southeastern half of Utah. Composed of a layer cake of sedimentary rocks, with the oldest at the bottom and the youngest at the top, this Province offers a geologic history that is relatively easy to read. The rock layers are horizontal and disturbed only by erosion throughout most of the Plateau; there is very little folding and faulting in comparison to other regions of our country. Only laccolithic mountains (which formed as magma within the sediments) and true volcanic peaks, disturb the geometry; the La Sal Mountains, east of Moab, Utah, are laccoliths while the San Francisco Mountains, north of Flagstaff are volcanic.

For the most part, the rock layers range in age from the late Paleozoic to the early Cenozoic Eras; Mesozoic sediments dominate across much of the Plateau. Older rocks can be found in the deeper canyons; the Grand Canyon, for example, exposes rock from the Precambrian Era (at its base) to the Permian Period (at its rim). The youngest rocks of the Plateau are found along its northern and western borders where early Tertiary sediments comprise the Roan and Wasatch Plateaus, respectively. Well known Mesozoic formations include the arches of Arches National Park (Jurassic), the Cliffhouse Sandstone of Mesa Verde (Cretaceous), the massive Wingate Sandtone walls of the Colorado National Monument (Jurassic) and the Petrified Forest of northern Arizona (Triassic).

Much of the erosion, which has sculpted the spectacular canyons and rock monuments, has occured since the Miocene Period, when the entire region was lifted 5000 feet and the rivers of the Colorado watershed were energized; a cooler, wetter climate during the Pleistocene also augmented the erosive power of these streams. Today, caught within the rain shadows of the Sierra Nevada and Rocky Mountains, the Plateau is a mosaic of arid and semiarid ecosystems; only the highest elevations support forests.

Love Birds

By mid March most of our resident songbirds have paired off and are engaged in courtship behavior. As far as we know, they have no personal feelings for one another. Rather, they are responding to the lengthening daylight, which triggers their instinct to breed.

Mourning doves huddle together in the trees while cardinals, house finches and blue jays (yes, even the macho jays) offer morsels of food to one another. Most birds are not monogamous but will stay together for the breeding season, cooperating to build the nest and feed their ravenous offspring. Once the young are independent, the parents go their separate ways; some birds, such as robins, will stay together long enough to raise a second brood.

The Invisible Chorus

The ice has melted and western chorus frogs are calling from the wetlands of mid Missouri. These small tree frogs, usually under 1.5 inches in length, are gray or brownish in color with faint dark stripes on their backs; a white line across the upper lips is one of their better fieldmarks. Now that you know what to look for, good luck!

While their calls echo across swamps and wet prairies from late winter to mid spring, it is very difficult to observe the frogs themselves. The males usually sing from mats of vegetation that collect on shallow pools or sloughs but fall silent at the slightest disturbance. Your best bet is to sit quietly at the edge of a pond or marsh, watching for their vocal sacs to expand and contract as they resume their distinctive call. The latter is a rising "prreeep," resembling the sound of a thumbnail plunking the teeth of a comb.

The males usually sing through mid May and, unlike most tree frogs, deliver their calls day and night. Attracted by their song, females arrive to lay up to 1000 eggs at various locations throughout the shallows; these will hatch into tadpoles and then mature to frogs by late summer. Adults spend the warmer months in moist woodlands, hunting for insects and spiders in the understory; they seldom climb far from the ground. As the cold returns and their prey dies off, chorus frogs hibernate in moist soil beneath marsh grass or plant debris.

White on Green

Just as the landscape was starting to green, two inches of heavy, wet snow cover the lawns and shrubs this morning; only clumps of wild onion poke above the wintery blanket to celebrate this Irish Holiday. Snowfall on St. Patrick's day is certainly not unusual in the American Midwest and is downright common along the Colorado Front Range; indeed, March is the snowiest month in Denver.

Spring has been put on hold for a day but, by March, the sun is too high to allow winter to linger. Highs tomorrow should be near 60, today's snow will be but a memory and the moisture left behind will accelerate the greening.

Cows, Pigs and Whales

One of the most fascinating events in evolutionary history is the divergence of whales from terrestrial mammals during the Eocene. Recent DNA studies indicate that modern whales and dolphins evolved from ancestral artiodactyls, the even-toed ungulate family of cows, pigs, hippos, deer and camels.

Early in the Eocene, about 50 million years ago, the artiodactyls were represented by a hoofed, dog-like mammal. Within 5 million years, a branch of this family evolved into alligator-shaped, amphibious mammals that lived along the coast of Africa and southern Asia. By 40 million years ago, this group had become totally aquatic and looked like elongated dolphins. During this ten million year evolution, the nostrils migrated from the tip of the nose to the top of the head, the tail became incorporated into the body, the forelegs became fins, the hind legs were reduced and internalized and, by the end of the Eocene, horizontal flukes developed.

As the Eocene gave way to the Oligocene, 38 million years ago, these ancestral cetaceans spread throughout the oceans, soon diverging into the toothed whale and dolphin families.
Baleen whales, which feed by filtering krill and plankton from the ocean waters, would evolve from their toothed cousins in the mid Miocene, some 16 million years ago.

Nature's Gliders

Fifty or more turkey vultures circled above the Hinkson Creek valley, in south Columbia, last evening. No doubt enjoying the balmy conditions, they would soon settle for the night on wooded cliffs of the valley walls, roosting in large flocks.

Turkey vultures can be seen in Missouri throughout the year but are more common during the warmer months. After sunning themselves on boulders or dead branches through the early daylight hours, they catch thermals that develop by late morning, soaring above the countryside in effortless fashion. Skilled gliders with a 6-foot wingspan, they seldom flap their wings once airborne and are easily recognized by their habit of holding their wings in a shallow V. When soaring near the treetops, they often tilt from side to side, deftly catching the breeze.

Up close, turkey vultures are far less beautiful. Their small, red-colored head (gray-colored in immature birds) is featherless, an adaptation to their diet of carrion. Not equipped with the powerful talons or keen vision of hawks, owls and eagles, vultures locate dead animals through their amazing sense of smell. And unlike those large raptors, they do not build nests; rather, they lay their eggs on rock ledges, in hollow logs or directly on the ground.

Evolution and the Pleistocene

The Pleistocene Epoch, commonly referred to as the Ice Age, was just the latest of many glacial periods in our planet's history. Stretching from 2 million years ago to 10 thousand years ago, this Epoch was characterized by four glacial advances and three warm, interglacial periods; some climatologists believe that the Holocene, the Period in which we live, is just another respite from the cold.

The unstable climate of the Pleistocene likely had a dramatic influence on evolution over the past 2 million years, forcing rapid adaptations and favoring intelligent creatures. Homo erectus appeared in Africa at the dawn of the Pleistocene and reached southeast Asia within 100 thousand years; not equipped to deal with the cold, he stayed south of the periglacial region, migrating along the southern coast of Asia. Neandertals diverged from the human lineage some 200,000 years ago, moving northward into western Asia and Europe. Humans did not appear until 125,000 years ago but, by the end of the Pleistocene, had spread to every continent except Antarctica. Low sea levels, resulting from glaciation, facilitated their dispersal.