[bright music] [insects buzzing] [gentle music] [crickets chirping] [gentle music continues] [horn solo] - Long ago, pioneers crossing the great Sonoran Desert named this peculiar object, the Apache boot, because of its shape.

It can only be found among stands of saguaro cactus, because in fact, it was once part of the cactus itself.

Hi, I'm George Page for "Nature," and amazingly, this Apache boot is what's left of a bird's nest, built inside a saguaro cactus by the Gila woodpecker.

The woodpecker, like the famous poisonous lizard, the Gila monster, gets its name from the Gila River, which joins the Colorado not far from this spot, near Yuma, Arizona.

What happens is this, the woodpecker makes a hole in the saguaro, like this one, then excavates a chamber downward, which becomes its nest.

The cactus reacts to the attack by producing a hard skin inside, much like a callous, that seals off the wound and protects the plant, and the woodpeckers have a perfect, naturally-insulated house.

When the cactus dies and falls down, most of it decomposes or rots, but the durable Apache boot remains and often becomes a home for other desert creatures.

This is just one of the many extraordinary things we'll learn about this giant cactus in our film by Wolfgang Bayer, "Saguaro: Sentinel of the Desert."

[gentle music] The great Sonoran Desert lies in the southwestern corner of North America.

Its most striking living feature is the saguaro cactus.

Its size and beauty draws the eye, but it's much more than a simple landmark to those that live on it or in it.

The interior of the cactus provides a secure nest for many creatures, a delicate and diversified community adapted to the extremes of the deserts day and night.

[owl hoots] [crickets chirp] [gentle music continues] Life in the desert depends on complex interrelationships between plants and animals.

[gentle music continues] Standing tall, a dramatic vision, this is the saguaro.

[owl hooting] Mention desert, and it's only natural to think of vast, trackless wastes of burning, drifting sand.

Visions of scorching winds coursing over the desolate dunes have made the word, desert, almost synonymous with lifeless.

[wind blows] The Sonoran Desert is hot and dry, but hardly lifeless.

This desert is more like a special forest whose trees are strikingly unusual.

[birds sing] To many, the image of the saguaro cactus epitomizes the look of the American West.

Ranging across the southern half of Arizona and even into Mexico, the saguaro stands as a vivid contradiction to the thought that the desert is lifeless.

Sometimes reaching heights of 50 feet and weighing as much as 10 tons, the saguaro is the largest member of the cactus family in the United States.

In countless ways, the giant cactus offers the necessities of survival to a wide range of desert life.

The gilded flicker finds at an ideal location to nest, as does the screech owl.

Even a dead saguaro held upright by its internal lattice work of wood supports provides shelter from the harsh environment.

A pack rat escapes the heat.

[crickets chirping] Below, in the root system, a rattlesnake hunts for food.

[crickets chirping] Even bats occasionally roost inside a decaying saguaro.

Too big to find space inside the cactus, a great horned owl, among the largest of the desert's predators, lives in its sturdy nest in the forked branches.

[wind blows] Also occupying the upper niche of the food chain are the hawks.

[insects buzzing] [wings flap] The Harris hawk builds its nest in the forks of only the largest saguaros.

High off the ground, the chicks can grow the maturity in perfect safety.

[insects buzzing] [hawks squawks] The Harris hawk is the only bird of prey that lives in a cooperative society.

As many as eight hawks, all from the same family group, will live in one area, often hunting together like a wolf pack.

Last year's chicks, now nearly full grown, help out in hunting food for this year's newborn chicks.

Sitting motionless on its high perch atop the cactus, the hawk keeps a sharp lookout for prey.

[insects buzzing] [wings flapping] The rabbit, a mainstay in the hawk's diet, is too heavy to lift, so the hawk drags it back to the shade.

After eating its fill, it carries parts of the carcass to its young in the nest.

While other hawks in the extended family may help gather the food, only the parents do the feeding.

[chicks chirp] [insects buzzing] The female shreds the food and tries to distribute it equally among her brood.

[chicks chirp] Although the unusually close social behavior of the Harris hawk has been amply documented, scientists are at a loss to explain this maneuver.

Up to four hawks have been seen stacked up like this on the tip of a cactus.

Perhaps back standing is the only way they can roost together.

The adult Harris hawk has no natural enemies in the desert, but if they move too close to another bird's nest, such as this western kingbird, the smaller and more agile bird can pounce on the hawk almost at will, annoying the bigger bird enough to make it leave.

The hawk rules the daytime sky, but the night belongs to another large bird of prey.

[crickets chirping] [owl hoots] The great horned owl, the nighttime counterpart of the hawk.

The owl is an opportunist.

Instead of building its own nest, it commandeers one that has already been built, usually that of a hawk.

The owl feeds largely on gophers and pack rats, and like the hawk, often catches rabbits.

But even though the two birds may live side-by-side, they hunt at different times, therefore minimizing competition for food.

The nighttime desert provides excellent hunting.

Rodents avoid the searing midday sun by becoming nocturnal and may become prey for silent hunters like the great horned owl.

[crickets chirp] The real competition for food is not between birds of different species, but between chicks in the same nest.

[crickets chirping] [crickets chirping] [crickets chirping] Though this young one has obviously had its fill, its watchful parent knows the job is never done and slips back into the night to search for more.

The unique boot of the saguaro cactus, originally excavated from its soft flesh by a woodpecker, is now home for the tiny elf owl, one of the smallest owls in the world.

Adults are only six inches long and the young find lots of room and safety in an abandoned nest.

What it lacks in stature, it makes up in numbers.

The most numerous bird of prey in the desert, it hunts flying insects such as moths.

Like most owls, they hunt at night and spend the daylight hours sleeping.

[crickets chirping] In another boot, a pair of slightly larger screech owl chicks finds their quarters crowded, but secure.

[crickets chirping] The adult prefers to escape the confined conditions and naps on the porch.

[animals calling] The architect of the boot is almost always the Gila woodpecker, often known as a carpenter bird for its skill at carving the raw cactus into a comfortable sanctuary.

[woodpecker pecking] The male and female take turns gathering food and babysitting.

The woodpecker feeds on the abundant insects found in and on desert plants.

The female, returning from gathering food, relieves the male.

The woodpecker does not line its nest.

Apparently, the bare interior of the cactus boot is comfortable enough.

Another woodpecker's home seems safe from intrusion, but not so.

The eastern starling has invaded the Sonoran Desert and poses a potential threat to the native birds.

If the starling sees an unguarded nest with no young, it will steal it from the woodpeckers.

All the starling needs is a second.

[bird caws] The unwary woodpecker, away from its nest only a moment, has lost its home.

Often, woodpeckers must make three or four nests before they can raise their young in peace.

For the starling, possession is nine tenths of the law.

[animals calling] Woodpeckers may begin several nest holes before completing one.

This apparent overabundance is misleading, because many of them are too shallow for nesting, but any hole that's big enough becomes home to somebody, such as these sparrows.

At the height of the breeding season, all the choice real estate has been taken.

The cactus wren does not rely upon homes built by others, but constructs an enclosed nest of woven grass, lined with feathers to protect its chicks from both heat and cold.

The lofty cactus is the perfect sanctuary from predators.

[animals calling] The Sonoran Desert is not always burning hot.

Snow, though rare, is not unusual.

Winter in the land of the saguaro is brief.

Most of the birds migrate to find warmer climates, but reptiles, such as rattlesnakes, need to find shelter from the subfreezing temperature.

[snakes rattle] To help reduce their heat loss, great numbers of rattlesnakes often hibernate together in underground caves.

But spring is never far off.

The first warming rays of sun bring out the sleepers, the western diamondback.

And the chuckwalla bask in the welcome warmth.

[dove coos] The birds return, the coo of the doves is only one of the many songs heard in the cactus forest.

[birds singing] [insects buzzing] [cardinal chirping] The winter brought rain and moisture to the desert, and in spring, the once forbidding landscape is blanketed with flowers.

[insects buzzing] [animals calling] Desert flowers, like larkspur, daisies, and brittlebush bloom briefly, but the explosion of color quickly subsides.

The short spring fades into hot summer.

[birds chirping] Late May, the saguaro begins to bud.

In the heat of the day, the buds remain tightly closed.

[insects buzzing] Birds wait expectantly for the sun to set, anticipating the singular event to come.

[owl hoots] Then, in the cool hours of dusk, the miracle happens.

[gentle music] [gentle music continues] [gentle music continues] [gentle music continues] [gentle music continues] Each bud opens only once and closes the next day, never to open again.

[gentle music continues] The night creatures are quick to take advantage of the rich feast.

Nectar-feeding bats are welcome dinner guests.

Their migration north from Mexico follows the wave of the ripening blossoms.

Their long snouts and tongues are perfectly adapted to drink the nectar deep within the blossoms.

In the process, they carry a dusting of pollen to the next saguaro, thus cross-pollinating the cactus.

[gentle music continues] Both plant and bat have evolved to rely on each other.

[owl hoots] [birds sing] At dawn, the bats retreat to their roost, leaving the blossoms to other feeders.

[insects buzzing] The large white flowers, perched conspicuously on its high arms, attract other potential pollinators.

Bees descend on the blossoms in great numbers, wallowing in the protein-rich pollen, and searching for the sweet nectar.

[bees buzzing] The bee's only concern is to harvest the nutritious pollen and nectar for its hive, but its efforts may also result in the transfer of pollen from cactus to cactus.

[bees buzzing] [bees buzzing] [bees buzzing] Briefly, the luxurious blooms provide a banquet to many of the desert's inhabitants.

The birds must be quick to take advantage of the rich bounty.

[insects buzzing] [insects buzzing] The flowers close in the heat of the day.

[insects buzzing] They die and drop off, their purpose fulfilled, the pollen has been dispersed.

In a month, the fruit will ripen.

[insects buzzing] As the days become hotter, the desert animals confine their activity to the cooler morning hours.

[insects buzzing] Water begins to disappear.

The road runner and coyote have found the last remaining water.

Briefly, the few dwindling pools support a variety of activity.

Quails drink their fill, as bees and wasps buzz over the last free moisture of the dry season.

[insects buzzing] Ultimately, the sun has its way.

The desert shrivels in its heat, but life goes on.

[insects buzzing] [road runner running] [road runner running] A road runner searches for prey and flushes out a bull snake.

[insects buzzing] [insects buzzing] The road runner is quite adept at catching snakes.

It uses its superior speed and distracting maneuvers to confuse the snake and tease it into striking until it's exhausted.

This technique not only works with a nonpoisonous bull snake, but also on the more dangerous rattlesnake.

The road runner finds its opening and its meal.

A vulture rides the thermals, searching for casualties of the withering heat.

[insects buzzing] Only insects, such as cicadas, are active at midday when summer temperatures reach 115 degrees or more.

[insects buzzing] [insects buzzing] [insects buzzing] [insects buzzing] The saguaro is well adapted to this heat.

Its spines, actually highly modified leaves, provide shade from the sun's rays.

Each spine's shadow may be minute, but the sheer number of them cool the cactus significantly.

The accordion-like pleats of the waxy skin enable it to expand when water is plentiful and contract when it's not.

At first glance, the skin appears smooth and featureless, but magnified a thousand times, its true texture is revealed.

Tiny holes called stomata open only at night.

They enable the cactus to breathe, so that photosynthesis may take place and form new tissue.

In the absence of green leaves, this process occurs on the saguaro's surface.

Other plants store what moisture they can in their roots and let leaves and branches wilt away to reduce water loss.

The animals have also adapted to the harsh conditions.

The desert cotton tail must survive on a diet of dried seeds.

Its blood engorged ears help to cool its body by dissipating excess heat.

[rodent rustling] Superbly adapted to desert life is the kangaroo rat.

Neither kangaroo, nor rat, it's nocturnal, avoiding the worst part of the day.

Its kidneys are so super efficient that the rodent never needs to drink water.

It can absorb enough moisture from the seeds it eats to survive.

[rodent rustling] [insects buzzing] Reptiles, with no internal mechanism to regulate their body temperatures, have no choice but to hide from the heat.

[insects buzzing] The hawks and other birds have few regulatory adaptations to deal with the heat.

While the adult birds may be able to fly off to find shade, the chicks, confined to their nest on top of the cactus, resort to panting to cool off.

The same is true for owls.

By contrast, those that live inside the body of the saguaro are the lucky ones.

90% of the cactus is water, which insulates against the heat, keeping the nest as much as 10 degrees cooler than the outside.

At night, the warmth absorbed during the day radiates into the nest, offsetting the evening's chill.

Those that nest within the saguaro are thus spared the daily extremes of temperatures.

[insects buzzing] During the time of the summer solstice, the long hours of sunlight ripen the saguaro's fruit.

[wings flap] This white-winged dove waits expectantly for the impending feast.

[insects buzzing] And then, in the hottest part of the summer, there's plenty of food in the desert.

[insects buzzing] The saguaro fruit splits open, exposing the red-pulpy interior, which is rich in nutrients and full of seeds.

A single saguaro can produce several million seeds in a lifetime.

The desert birds take advantage of the abundance.

[insects buzzing] [saguaro fruit falls] The fruit litters the ground with food, drawing other desert inhabitants into the open.

Collared peccaries or javelinas supplement their diet with the saguaro fruit.

[animals calling] Other animals enjoy the brief time of plenty.

Any leftovers are efficiently whisked away by hordes of carpenter ants.

[upbeat playful music] [upbeat playful music continues] [upbeat playful music continues] [upbeat playful music continues] Each cactus can produce as many as 100 fruits in a season, and each fruit contains about 2,000 seeds.

In some places, 90% of those seeds will be taken by the ants.

[crickets chirping] The fruit isn't the only meal available at this time.

There are those who come to feed on the feeders.

The horned lizard hardly needs to move.

Its dinner walks right by in front of it.

[crickets chirping] The pickings are easy.

[crickets chirping] [crickets chirping] [birds singing] Summer's bounty means food for the desert inhabitants and the certainty that the saguaro seeds will be spread far and wide.

The fruit is also popular with other residents of the desert.

[animals calling] The Tohono O'odham Indians have lived in the area and harvested the saguaro fruit for centuries.

Using long poles of saguaro wood, they gather the fruit to make syrup, jam, and ceremonial wine.

[harvester talking] Mary Miguel holds on to the tradition, which is slowly fading away.

- [Mary Voice-Over] I remember when I was a little girl, my grandmother used to go out and pick saguaro fruit.

We'd pick 'em up and we'd split the fruit and put it in a pail, and we picked the dry ones, and we mixed it up, and when our pail gets full, we bring it home, and we dump it in the top and put water in there.

And when they get wet, we mix it up, squash the seed, and then we cook it and drain it out.

And we usually make about 10 gallons of syrup, 15 gallons of syrup, and then we start on our jams on the last part of the harvest.

[jam bubbling] [bright music] - [George] According to an ancient Tohono O'odham tradition, the end of the harvest foretells the beginning of the rainy season.

As soon as the harvest is brought to a close, clouds are seen approaching.

Soon thereafter, it rains.

[wind blowing] [thunder cracking] In early July, the weather patterns in the tropics drive moist air up over the desert, and the rains come.

[rain falling] Soon, the desert is alive and green again.

Water is plentiful, and plants flourish in the moist soil.

[birds calling] Those few saguaro seeds, lucky enough to have been deposited under a protective nurse plant, may now begin to grow.

Shielded from temperature extremes and hungry animals, the tiny cactus grows very slowly.

After two years, it may be only a quarter of an inch in diameter.

A nine-year-old plant like this may reach just six inches in height.

These are the perilous years for the saguaro.

Out of the millions of seeds produced, only a precious sheltered few survive to outgrow and replace their nurse plants.

High winds or lightning uproot older saguaros, killing the cactus, but creating an environment of a different and unexpected type.

A large saguaro can weigh as much as 10 tons, most of which is water.

Its death creates a temporary oasis.

As a fallen cactus decays, plenty of moisture becomes available, so much in fact that a certain species of aquatic beetle finds a comfortable home in the pulpy interior.

Aquatic beetles usually live in ponds or swamps, but these have adapted to life in the desert.

Their keen sense of smell can lead them unerringly to a decaying cactus.

[insects buzzing] This slimy environment also has its villain.

The hister beetle is the local predator.

Half an inch long, it plows through the rotting cactus in search of fly larvae and small insects.

Its slick carapace enables its thin body to slice like a knife through the sticky mire.

[insects buzzing] [insects buzzing] Many saguaros remain standing after they die, held upright by the wooden framework of the ribs within.

[birds calling] The wreckage of these hulks supplies a dry home for other creatures.

[dramatic music] The black widow spider prefers the dark recesses of a dead saguaro where it spins its web, waits for prey, and lays its eggs.

[dramatic music continues] Maternal care is not a strong point with the black widow.

Her young are on their own as soon as they're hatched.

[dramatic music continues] The tiny spiderlings crawl to the top of a cactus spire and release a filament of silk from their spinnerets.

The first breeze that drifts by whisks the young spiders out into the world and to their own fate.

It's called ballooning.

[dramatic music continues] The same space provides a home for the cactus mouse, which nests in the center of the dead cactus.

[crickets chirping] Under the dry debris of a fallen cactus, the pack rat often builds its nest.

The rodent forages at night, bringing seeds, flowers, and cactus fruit back to its underground den.

The floor of its home becomes covered with its collection, which is cemented together by its own excretions.

Amazingly, the pack rats untidy habits supply valuable knowledge about the history of the Sonoran Desert.

Dr. Tom Van Devender, a scientist from the Arizona Sonoran Desert Museum, studies the waste piles called middens from ancient pack rat nests, searching for clues about the desert's past.

- [Tom Voice-Over] I view myself as a paleoecologist.

That means I look at the relationships of plants and animals and their environment through time.

The main tools that I use are pack rat middens.

These are organic deposits which are built by pack rats, and they're preserved in dry rock shelters.

And they contain plant fragments that are very well preserved, and you can identify them usually to the particular species of plant, and you can radiocarbon date them.

And so, we really look at these little collections of plant fragments through time, and we are able to record changes in the vegetation in desert areas in the last 30 or 40,000 years.

- [George] In the laboratory, saguaros seeds are isolated from the specimen.

The ancient seeds are then treated to render microscopic bits of carbon, which are run through the carbon dating process.

[machine humming and whistling] The computer tells Dr. Van Devender that this specimen is about 6,600 years old.

He has found that the saguaro reappeared here around 10,000 years ago, shortly after the last ice age.

An even older Sonoran resident, man, first appeared in this section of the continent 12,000 years ago, and he left his mark permanently etched in the stone.

First, the prehistoric Hohokams and the Tohono O'odham Indians lived in the area.

But it was the advent of the white man that had the most impact on the desert.

The land was ceded to the United States from Mexico in 1853 via the Gadsden Purchase, and in 1879 the railhead reached Tucson.

With the railroad came the first tourists.

Some saguaro cacti, alive today, are old enough to have witnessed the Old West flourish, and then become a dusty memory.

[wind blows] The saguaro survived the day of the Wild West, but a new kind of threat was yet to come.

With the arrival of the railroad, cattle herding became profitable, big business, and soon, the desert was overrun by herds of hungry cattle.

[cattle running] [cows mooing] Overgrazing of the saguaro forest was the worst danger it had ever faced.

The fragile ecosystem was nearly destroyed by man's ignorance.

By comparing historic photographs with those taken more recently in the same area, one can see the devastating effect the cattle had on the desert.

Fearful that this precious environment would be lost forever, in 1932, the United States Government set aside the land for Saguaro National Monument, hoping to preserve a part of this desert and its unique wildlife for future generations.

[birds chirping] [insects buzzing] In some cases, the Saguaro and its attendant species can coexist with man's progress, but just as often, the saguaro is in the way.

Man is still moving in.

As the popularity of the Sunbelt grows, so do the towns and cities in the desert.

Real estate is booming and the saguaro takes a backseat to the expansion.

[tractors rumbling] At some construction sites, the threatened cacti are saved.

To move a 20 foot plant, bristling with piercing spines, takes great care, but a large one like this can bring $500 at a commercial nursery.

[workers talking] - [Worker] Come on baby.

- [George] Because the saguaro's root system is so shallow, it's easily uprooted.

A state permit is required to transplant a cactus, and they're usually granted to move plants away from construction projects.

[bulldozer rumbling] On large construction sites, however, the cost of transplanting the cactus is considered excessive.

The saguaro is just an obstacle to be rid of.

In the cause of progress, the bulldozer has the final say.

[bulldozer rumbling] [bulldozer rumbling] Ironically, the removal of a single saguaro without a permit is a crime, carrying a fine of $500.

[gun firing] In other situations, the cactus is killed piecemeal, ignored as if it weren't there.

Lead is as deadly to the saguaro as is the bulldozer's blade.

[bright music] Yet, the great cactus remains an important symbol to the people of the area.

[bright music continues] [bright music continues] [bright music continues] Greenhouses grow saguaros under controlled conditions with phenomenal success.

In the wild, the odds are as high as 20 million to one that a seed will grow to maturity.

In the greenhouses, as many as 90% survive.

One greenhouse can sell as many as 200,000 saguaros a year.

But the saguaro is much more than a commercial commodity.

Study of the cactus is of extreme importance if the dynamics of the desert are to be understood.

[insects buzzing] Dr. Charles Lowe of the University of Arizona Tucson is a pioneer in saguaro research.

36 years ago, he led the team that discovered the cause of an apparent epidemic that was killing the cactus throughout the Sonoran.

- [Charles Voice-Over] Now the work began in the 1950s when we realized that freezing was killing saguaros and not the so-called bacterial necrosis disease.

Freezing occurs in the wintertime.

The results of those freezes are often not seen until later in the year in the spring, in April and May, when the weather warms up and then dripping is seen, a brown to black dripping of a bacterial material, which actually is a decomposing bacterium that is set in the saguaro on the dead and dying tissues caused by freezing.

Often while walking through the Sonoran Desert, you will see large saguaros with many twisted, bent arms.

These are the result of freezing during the January freezes.

The freezing taking place at the base of the arms causes the heavy weight of the arm to bend downward in the twisted, deformed picture that you see long after the freeze is gone.

The freezing rings you see, usually at the base of saguaros in this area, are due to freezing of the plant when it was smaller.

The crown froze.

The plant did not die.

It regrew from that area, which was the top of the smaller plant.

- [George] Like a doctor making house calls, Lowe spends countless hours with his spiny patients.

[Dr. Lowe climbs] He records and monitors temperature variations, learning how the plant responds to the extremes of a typical desert day.

[insects buzzing] Through the efforts of people like Dr. Lowe, we learn more about this unique plant and its relationship to the changing environment.

[Dr. Lowe descends] [animals calling] As the saguaro lives, so will the delicate web of life of which it's apart.

Once the web has been broken, the desert may become lifeless indeed.

[bright music] As some flowers close, others prepare to open.

Life in the desert is a continuing renewal of nature's miracle.

The saguaro cactus stands like a sentinel, but it's more than a dramatic symbol of the American West.

It's the guardian of life's outpost in the desert.

[bright music continues] [crickets chirping] [animals calling] The story of the saguaro is just another reminder of the awesome natural wonders we can still find in those areas of our great country, which have escaped the bulldozer, the concrete, and the asphalt.

I'm George Page for "Nature."