Owls Aren't Wise and Bats Aren't Blind (16 page)

This trill evidently serves to attract female toads and perhaps gives them an indication which male might make the best mate. Mating takes place when the smaller male toad climbs on the female’s back and uses his front legs to hold her tightly in a grasp known as
amplexus.
During breeding, males have horny pads on the first two toes of each front foot to aid them in holding the female.

The female lays her eggs during amplexus; unlike frogs, which lay their eggs in a large clump, the toad’s eggs are encased in two long, slender strings of gelatinous material. These strings can exceed sixty feet in length and contain up to fifteen thousand eggs! Meanwhile, the male fertilizes the eggs as they slowly emerge from the female.

Male toads aren’t overly endowed with brains when it comes to mating. They often try to mate with almost anything that floats and moves, such as sticks, leaves, and even other male toads. Indeed, a male toad suddenly squeezed in amplexus by another male often (and justifiably) squeaks indignantly until the offender releases him. Eventually the eager but misguided male lets go of stick, leaf, or other male and moves on until he successfully locates a female.

Whenever submerged plants are available, toads prefer to weave their egg strings among them, although the eggs aren’t actually attached to the vegetation. We’ve often observed this behavior in our pond. First, the mating pair, with the male on top gripping the much larger female in amplexus, appears on the surface. After breathing for a brief period, the two dive to reach underwater growth at a depth of two or three feet. Still plainly visible in the pond’s clear water, the couple moves slowly among the plants while continuously laying down the two strings of fertilized eggs. After perhaps five minutes, the toads drift to the surface to breathe again, with the trailing egg strings still attached to the female. This cycle is repeated over and over until egg-laying is done and the two toads separate.

Depending on water temperature, the eggs hatch in anywhere from three to twelve days (the warmer the water, the shorter the time until hatching). The tadpoles, often humorously called “toadpoles,” can easily be distinguished from frog tadpoles because they’re black. They often move in schools, and feed hungrily on algae and minuscule bits of organic debris, all the while growing steadily. Just as steadily, a variety of predators take their toll; these include dragonfly larvae, predaceous diving beetles, fish, and leeches.

When they are just under a half-inch long, the “toadpoles” begin their metamorphosis. As with other frogs and toads, the tadpoles begin to absorb their tails and develop legs. This process continues for approximately two months. At the end of that time, the young are fully formed little toads, ready to leave the water for the second part of their dual lives.

When the young toads begin their migration onto land, they present quite a spectacle. Only about a third of an inch long, they swarm up onto the land by the hundreds, so small that at first glance they may be confused with insects. Under normal conditions, the toadlets disperse rapidly, heading off in all directions to seek suitable habitat. Under drought conditions, however, they may gather in moist places to await better conditions for dispersal.

A young toad sheds its skin every few weeks while it’s growing rapidly, whereas an adult dispenses with its skin four times a year. This molt is a rather comical procedure, at least from the human standpoint. First the skin splits. Then the toad uses its front feet to pull the old skin off, gradually stuffs the castoff suit into its mouth, and finally swallows the whole affair! The entire procedure takes only about five minutes, and the toad then goes blithely on its way.

Our common toad is notably uncritical about terrestrial habitat, which may be one reason for its evolutionary success. Fields, all sorts of forests, moist areas, gardens, yards, and almost anything else are suitable for the toad, as long as it’s not excessively hot and dry, with no shade or moist dirt in which to shelter.

Toads are equally unfussy eaters. A wide variety of insects, slugs, earthworms, and assorted other small creepy-crawlies appeal to their catholic tastes and are snapped up with gusto, to the great benefit of many plants— including those in our gardens. Like frogs, toads have the unique feature of a long, sticky tongue attached in the front of the mouth, rather than at the rear. This marvelous adaptation enables the toad to flick its tongue forward with lightning rapidity to snare its unwary prey and just as quickly flip it back into the wide, gaping mouth.

Although predators wreak the greatest havoc on toads while they’re either tadpoles or very tiny toadlets first emerging onto land, adult toads aren’t immune, but the toxins produced by the glands on a toad’s skin repel many predators, especially those that have had previous experience with toads. Domestic dogs and house cats, for instance, are known to learn that toads are distasteful. No doubt many wild predators are equally deterred by the toad’s defenses, although raccoons and skunks evidently are predators of toads. Snakes are probably the toad’s most serious predators, however. Many species of snakes seem to be unaffected by the toad’s toxins, and some snakes feed very heavily on toads.

Toads also have a rather peculiar reaction to danger. When startled or frightened, they may release a quantity of liquid that is generally thought to be urine, but in fact is water stored away by the toad against a time when drought might threaten it. How successful this technique is in repelling predators is questionable. I well recall that, when I was a small boy, my play-mates and I used to call toads that reacted in this fashion “pee toads” and giggled a little self-consciously about it, as small children are wont to do about such things.

Like other amphibians, toads are cold-blooded, so with the onset of cold weather they begin to look for a place to hibernate. Suitable locations include burrows in soft soil or the soft, loose litter of the forest floor. In places such as this, toads can become dormant for the winter, secure from bitter weather and the attacks of predators.

Toads become sexually mature when they’re three years old. When they emerge from their winter’s sleep during their third spring, that deep, ancient instinct to mate and perpetuate the species finally asserts itself. Then the breeding grounds issue their mysterious, irresistible siren call, and the toads temporarily forsake their terrestrial habitat to wend their way in slow toad fashion back to the most ancient habitat of all—water. There they will continue the unending cycle that has repeated itself for countless millions of years.

Despite their newfound favor in some circles, toads have generally been regarded, at best, as rather plebeian creatures—useful, perhaps, but without the slightest hint of glamour or excitement. How ironic it is, therefore, to learn that the lowly toad may yet prove to be the savior of some of its more charismatic relatives.

The Center for Research of Endangered Wildlife (CREW) and the Herpetology Department of the Cincinnati Zoo are busily engaged in developing assisted reproductive techniques to help propagate endangered species of toads and frogs. Oddly enough, their quest started with an old test originally formulated for humans, rather than for frogs and toads.

The Galli-Mainini test was developed fifty years ago to determine human pregnancy. It was discovered that male toads injected with urine from a pregnant woman began to release their sperm, while the urine of non-pregnant women had no effect. Evidently the human pregnancy hormone replicates the hormone normally released in the male toad during amplexus.

The CREW team first tested different methods of introducing human urine into the toad in order to attain maximum effectiveness. Application on the skin of the back had no effect, and application on the skin of the abdomen only induced sperm release in about one-third of the males. Injection under the abdominal skin caused some sperm release, but by far the best results were obtained by injecting the urine into the toad’s abdominal cavity.

Using this technique developed with the common toad, CREW and the Cincinnati Zoo have successfully bred endangered toads (and ultimately will breed frogs, one would assume) and released their offspring into the wild. The poor relation, it turns out, is not so poor after all!

During cool, damp weather, toads are active both day and night. When the weather turns hot and dry, however, they burrow into soft soil, forest litter, or beneath some other shelter. There they wait through the heat of the day, emerging at dusk to forage during the cool, damp night.

On numerous hot summer evenings, as my wife and I have sat in front of our house to watch the evening bat circus, we’ve heard tiny noises as dusk settles—perhaps a slight scratching or scraping, or the movement of a small pebble. Peering around us, we’ve been able to see a toad that has just emerged from beneath the huge, flat stone that constitutes our doorstep. There, in relative coolness, the toad waited out the heat of the day.

At first the toad’s movements are cautious and tentative—a single hop, followed by total immobility for several minutes. Then comes another hop, followed by another pause. Then, as twilight deepens, the toad seems to gather confidence; soon it hops slowly but steadily away, quickly disappearing in the gathering gloom. Toads are abroad again, seeking sustenance, and we’re left with the comforting feeling that one more thing is right with the world.

Great horned owl
(rear);
barred owl
(center);
saw-whet owl

11

Not Wise, But Otherwíse: Owls

MYTHS

Owls are wise.

Owls only make hooting sounds.

Owls are blind, or nearly so, in bright daylight.

An owl’s ears are visible.

Some owls can carry off many times their own weight.

OWLS HAVE BECOME THE UBIQUITOUS SYMBOL OF WISDOM IN MODERN SOCIETY. No matter which way we turn, anything connected with wisdom or intelligence is apt to include a representation of an owl. Advertisements of the “Be wise, modernize” sort, for example, usually sport a drawing or photograph of an owl. Then there is the oft-repeated bit of doggerel, “A wise old owl sat in an oak. The more he saw, the less he spoke . . . Why can’t we be like this wise bird?” slightly modified from its original 1875 incarnation in
Punch.

It was not always thus, however. In the past, owls in many cultures had a sinister reputation. This was quite possibly because owl hoots have generally been considered “mournful,” and hence have associated owls with death and a variety of ill fortunes.

Shakespeare certainly believed that, or at least used the common superstition for dramatic effect. In
Macbeth,
Lady Macbeth takes the cry of the owl as a sign that her husband has murdered Duncan (“It was the owl that shriek’d, the fatal bellman . . .”). A little later in the play, the owl becomes a symbol of the weird atmosphere surrounding Duncan’s murder: “’Tis unnatural . . . on Tuesday last, a falcon, towering in her pride of place, / Was by a mousing owl hawk’d at and kill’d.”

Not everyone considered owls to be the bearers of misfortune, however. For instance, a small owl in ancient Greece was so highly regarded that it became the mascot of the powerful Athenian army. The owl was one of the symbols of the goddess Athena and of the city of Athens. It was portrayed on Athenian coins, with the head of Athena on the reverse side. Other societies also valued the owl as a bearer of good fortune—perhaps even as a symbol of wisdom. It’s doubtful, however, that any previous society has placed as much emphasis as ours on the owl’s reputed wisdom.

Why have we endowed these birds with such an aura of great wisdom? The answer seems to lie in the owl’s facial structure and large, staring eyes. An owl’s eyes are set squarely in the front of its head, an avian feature shared only by penguins. This eye placement conspires with the feathered facial disk to give the owl a vaguely human appearance. In addition, those big, staring eyes lend an almost professorial appearance to owls, much as horn-rimmed glasses might to a human. Anthropomorphism does the rest; if owls remind us of ourselves, they must therefore be intelligent.

Appearances notwithstanding, the sad truth is that owls don’t rate very high on the intelligence scale, even among birds. Members of the Corvidae—ravens, crows, jays, magpies, and the like—to use just one example, are undoubtedly far smarter than owls. Upon careful consideration, it shouldn’t come as any great surprise that owls rate as something of dim bulbs among their bird brethren. After all, so much of an owl’s skull capacity is taken up with the apparatus necessary for vision and hearing that there’s little brainpower left for “wisdom”!

We actually do owls an injustice by regarding them as wise, for in so doing we obscure their true nature. Owls are, above all else, superb killing machines, with astonishing adaptations for taking their prey. With their almost unbelievably sensitive hearing and eyesight, as well as virtually silent flight, owls possess a phenomenal ability to locate and seize a variety of prey by night or day.

Take eyesight, for instance. An owl’s eyes are one hundred times more sensitive to light than human eyes. Even on a dark night, owls can see details of landscape and prey with great clarity. Because most owls are night hunters, it’s popularly supposed that in bright daylight they see poorly at best, and are perhaps nearly blind. This is a misunderstanding that dates far back in time. Tennyson, among others, certainly believed this myth when he penned the line “. . . and thrice as blind as any noon-tide owl. . . .” However, owls can see equally well in darkness or daylight.

Why, then, are most owls mainly abroad at night? There are at least two good reasons. First, this is the time when the majority of their prey species are most active; mice and other small rodents, for example, are far more apt to be afoot at night than in daylight. Second, they have no nighttime competition from other raptors—notably hawks and eagles. Equipped by nature with superb tools for night hunting, owls have thus been able to preempt an important ecological niche.

Because of their size, structure, and placement, an owl’s eyes are immobile, but the owl compensates with a unique adaptation. In both birds and mammals, the first vertebra below the skull is called the
atlas
because, as Atlas supported the globe, it holds up the skull. Mammals have an atlas with two cups that fit against two projections on the skull; this arrangement severely limits the ability to turn the head.

Birds, on the other hand, have a single cup-and-skull projection, a system that greatly facilitates movement of the head. Owls have further perfected this useful anatomical feature. In consequence, an owl can swivel its head not merely 180 degrees to look backward, but 270 degrees—three-quarters of a full circle.

I first observed this trait many years ago while watching Spooky, the resident great horned owl
(Bubo virginianus)
at the Museum of Science in Boston. Fascinated by its huge, yellow eyes, I somehow conceived the idea of a staring contest to see who would blink first. It was a difficult struggle at first, for I had to exercise a great deal of determination to avoid blinking. After a substantial time, however, I “won” the contest—not because Spooky blinked, but because I suddenly found myself staring at the back of its head!

After a few seconds the owl snapped its head forward again, and a somewhat briefer staring contest ensued. Then I once more found myself viewing the back of Spooky’s head. This sequence was repeated several times more, with each staring episode becoming shorter and shorter. Finally it reached the point where the owl was taking only a split second to see that I was still staring—then snapping its head backward, then forward, then backward, and so on. At that point, fearful that the owl would twist its head off, I took pity on the distraught creature and left poor Spooky in peace. Clearly, a great horned owl doesn’t appreciate having its stare returned—at least for any length of time!

Owls’ hearing is even more astonishing than their eyesight. Indeed, despite superb nocturnal vision, owls hunt at night more by sound than sight. So incredibly sensitive is their hearing that, according to researcher Allen Eckert, some species of owls can hear a mouse squeak as much as a half-mile away! An owl’s hearing ability consists of far more than mere sensitivity, however; it also has a special adaptation enabling it to locate its prey’s position in three dimensions with uncanny precision. Indeed, experiments in the laboratory have demonstrated that sightless owls can catch mice by sound alone.

The ear cavities in an owl’s skull are asymmetrical, so that one ear receives more sound from above, the other more from below. This ear placement permits the owl to locate its prey accurately in the vertical plane. Simultaneously, an acute ability to process the infinitesimal difference in the time it takes a sound to reach each ear accomplishes the same thing in the horizontal plane. Also, the facial disk—a feature that helps give owls a vaguely human appearance—further aids this phenomenal hearing apparatus by capturing sound and reflecting it toward the ears.

If the prey makes the slightest sound while an owl homes in on it, the owl immediately “views” the location of the prey in three dimensions. Incidentally, what are widely regarded as “ears” on some owls are merely feather tufts that have nothing to do with hearing. The actual ears are only openings in the skull and are invisible.

Silent flight completes the package of adaptations that make the owl such a ruthlessly efficient predator. Exceptionally soft leading edges on flight feathers, combined with a very large wing area in relation to body weight, plus soft head and body feathers, make an owl’s flight almost noiseless. The mouse rustling in the grass or the rabbit hopping across a forest glade has no warning that death is descending upon it as the owl ghosts down for the kill. Not until talons seize the prey in a deadly grip does the victim have the slightest inkling of its fate. These days we make much of the technological wizardry of our stealth fighters and stealth bombers, but owls on ghostlike wings were nature’s original stealth aircraft long ages earlier.

Owls, even large species, subsist mostly on small mammals such as mice, voles, and lemmings. These are promptly gulped down whole, and then another adaptation—their unusual digestive system—takes over. Indigestible parts, such as bones and fur, are packed together into pellets by stomach action, then are regurgitated, thus efficiently ridding the owl of useless material. An owl’s favorite roosting place can sometimes be identified by the pellets beneath it. These pellets can also tell us much about an owl’s food habits. By dissecting and analyzing pellets, researchers can determine what species an owl has been feeding on.