Amazing Animal Insights

Sherry Seethaler

Reptile Romeos

We live in a home surrounded by a plethora of lizards. In observing them, I began to wonder, why do they do “pushups” while sunning themselves?

They are displaying athletic flamboyance like their human counterparts at Venice Beach. Depending on the nuances, lizard pushups may convey “I’m too tough to mess with” or “Hey, ladies, check me out.” Body language is a rich form of communication for lizard jocks and jockettes.

Other lizards can glean useful information from the unique characteristics of the pushups: overall body posture, pattern of head bobs, and how the legs stretch and flex. For example, the number of pushups performed by a male in a territorial interaction corresponds with his aggressiveness and pugilistic prowess. Therefore, a potential opponent can avoid a fight he has little chance of winning.

Lizard species have distinct pushup styles, and within a species, regional differences in pushup dialects often arise. Some scientists speculate that new species may emerge when regional pushup dialects diverge so much that males and females do not understand each other and courtship fails.

Individual lizards also have their own unique pushup flair. Even after scientists tuckered out lizards by making them run on a treadmill, their pushups maintained a reliable individual pattern.

Pushup styles have important ramifications for social behavior and kin recognition. For example, at territorial boundaries, lizards usually tolerate their neighbors, but not strangers. A lizard would waste energy if he harassed his neighbor every time he headed out to make his rounds, but he may need to put a new guy in town in his place.

Both male and female lizards do pushups in a variety of contexts, such as when encountering another lizard, when encountering chemical markings left by another lizard, or after moving from one location to another. Lizards may broadcast their presence whether or not other lizards are nearby.

Pushups and head bobbing may also play a role in vision. Humans and other animals with frontal eyes can determine the distance to an object by interpreting the slightly different projection of it onto each retina. With eyes on the sides of their heads, lizards have a panoramic view of the horizon. The arrangement is handy for spotting predators approaching from any direction, but it does not permit binocular vision.

Just as driving in a car makes nearby objects appear to move more quickly than distant objects, rapid motion of a lizard’s head reveals the relative distance of objects. Birds and other animals with widely spaced eyes also move their heads to gauge depth.

Desert Dwellers

How can camels go so long without drinking water?

Many of us remember being told as kids that camels store water in their humps. Backpackers will be familiar with Camel Baks or dromedaries (so-called for the one-humped Arabian camel, Camelus dromedarius) for carrying water. The hump actually is made of fat, which helps a camel survive for long periods without food.

Camels do not store water. Two sets of adaptations give camels their ability to survive for long periods (weeks) without drinking: 1) extremely efficient water conservation and 2) excellent dehydration tolerance.

Most mammals, including humans, need to keep their body temperatures relatively constant and cool down via evaporation of water by sweating or panting. Camels can allow their body temperatures to rise by more than 10° Fahrenheit (6° Celsius) on hot days, which reduces the need for sweating.

Adaptations of the digestive tract and kidneys permit the camel to produce dry feces and highly concentrated urine. Although other animals respond to dehydration by excreting less water in their waste products, few can do it as effectively as camels. In addition, the tough mouth of a camel allows it to eat thorny desert vegetation, which often has significant water content.

Because of these adaptations, camels dehydrate more slowly than other animals. But, camels can also survive losses of up to one-third of their body weight in water, twice the level of dehydration that would kill a horse. When presented with water, camels rehydrate remarkably quickly, within a matter of minutes.

Adaptations of camels’ blood facilitate dehydration tolerance and the ability to rehydrate quickly. Most animals lose a significant proportion of water from the blood when dehydrated. The blood becomes thicker and more difficult to pump through small blood vessels in the skin, where heat can be released to the environment. Fatal overheating can result.

In camels, water loss from the blood is reduced by the presence of a high level of a protein called albumin, which attracts water. When dehydrated, a camel loses most of its water from the digestive tract, which contains large quantities of liquid in an animal like a camel or a cow that has a multicompartment stomach.

Some water is still lost from the blood, but to deal with this, camels’ hemoglobin—the oxygen-carrying molecule in the blood—has a protein structure that is highly hydrophilic, or water-loving. As a result, camels’ hemoglobin better holds on to water and keeps it within the red blood cells.

Camels’ red blood cells are also unusually resistant to bursting when placed in a dilute solution and, therefore, can tolerate a rapid reuptake of water into the blood. The ability of camels’ red blood cells to swell significantly without membrane rupture may be due to a combination of their shape and membrane composition. Camels’ red blood cell membranes have a significantly higher protein composition compared to the red blood cell membranes of less-dehydration-resistant species, and this protein is thought to strengthen the membrane.

Members of the camel family, which include llamas and alpacas, are also the only mammals that have oval rather than circular red blood cells. The oval shape could alter the distribution of stresses on the membrane and confer rupture resistance. The oval shape also facilitates blood flow in the dehydrated state, as the streamlined red blood cells orient with the long axis in the direction of blood flow, reducing drag as they course through the blood vessels.

Phobic Pachyderm?

I’ve heard that elephants are afraid of mice. If so, for what reason?

Elephants are not afraid of mice, say elephant keepers at zoos and circuses. Stables provide mice with shelter, nesting material, and food, so captive elephants must grow accustomed to encountering mice. There is no reason to think wild elephants have musophobia, fear of mice. An elephant is unlikely to even take notice of a mouse.

The jokes and cartoons depicting elephants cowering at the sight of a mouse have ancient roots. Nearly 2,000 years ago, Pliny the Elder, ancient author and natural philosopher, wrote in his Encyclopedia of Natural History, “They [elephants] hate the mouse, worst of living creatures, and if they see one merely touch the fodder placed in their stall, they refuse it with disgust.”

It is not clear where Pliny got this information, but Natural History contains many fanciful things. For example, it is also responsible for propagating the myth that porcupines shoot their quills. Although his work is considered a major achievement in documenting knowledge about the natural world, Pliny relied a great deal on hearsay.

Just Hangin’ Around

Why do some birds gather in certain spots? I can see that the pigeons congregating in public places have found them to be a good source of dropped food. The birds that are more interesting are the ones that sit, sometimes in rows, on the wires that cross the freeway or on signs.

In areas with few trees, wires and signs are the highest available perches. Being high protects birds from predators and helps them spot sources of food. Lifting off from a high perch is also easier than lifting off at ground level.

Some of the birds may be perched near nests they built on the underside of highway overpasses. The wires and signs also serve as “staging” sites, where birds congregate between feeding areas and the places they roost for the night.

Various possibilities explain why there are gaggles of geese, bevies of quail, bands of jays, colonies of penguins, coveys of pheasants, broods of chickens, charms of finches—that is, why birds of a feather flock together. In some species, extended families help raise young. Flocking may also protect birds from predators. In support of this possibility, one study found that birds on islands with few predators flocked less than birds of the same species living near abundant predators. Other studies have suggested that flocking together helps birds locate sources of food.

Incidentally, birds’ affinity for power lines is a concern for utility companies, which can be held legally responsible for electrocuting them. Also, when large birds empty their bowels as they take off, these “streams” can bridge the gap between the transmission structure and the conductor, causing outages.

Classy Choreography

I’m curious about how flocks of birds and schools of fish can all change direction at once.

More than half of fish species form schools and half of bird species form flocks. Groups range greatly in size, from a few individuals to a 15-mile-long school of herring that the Department of Fish and Game biologists measured in San Francisco Bay.

Group formation provides protection against predators, facilitates foraging for food, and simplifies the search for a mate—rather like humans hanging out a nightclub.

Flocking and schooling are emergent properties, the collective outcomes of individual behaviors and interactions among members. No single leader controls group coordination; any member of the group can initiate maneuvers, which may travel along any axis, including from back to front.

Because maneuvers occur more abruptly than they could if individuals were simply reacting to their immediate neighbors, some researchers have postulated that animals coordinate group behaviors using “thought transference” or electric and magnetic fields. However, video analysis and computer simulations show that it is not necessary to infer unusual forms of communication to explain flocking and schooling.

Group coordination can be replicated by computer models in which individual “animals” follow three simple rules: stick close to neighbors, move away if neighbors are too close, and face the same direction as those nearby.

In nature, group members appear to follow the lead of initiators banking toward but not away from the group. Individuals that move away from the group are especially vulnerable to being picked off by predators.

To explain the swiftness of maneuver coordination, biologist Wayne Potts proposed the “chorus-line hypothesis” in the journal Nature in 1984. Potts conducted field observations and analyzed slow-motion frames of film taken of flocks of shore birds. He found that one individual or a few individuals initiated each maneuver, which then radiated from the initiation site to propagate through the flock in a wave.

The propagation of the wave began slowly but reached speeds two to three times as fast as would be possible, based on visual response times, if the birds were simply reacting to their nearest neighbors. Potts concluded that flocking birds were coordinating their behaviors just as humans do in a chorus line.

In a chorus line, maneuvers propagate from person to person almost two times as fast as the maximum human visual response time. This is possible because individuals watch the approaching maneuver wave and time their movements to coincide with its arrival.

It’s All a Blur

The human brain registers visual input at about 16 frames per second. I assume that some animals register visual input at other speeds. What variety is there? How did evolution shape this adaptation? What benefits are conveyed by the minimum or maximum?

In the early days of movies, it was determined that film had to be advanced at a minimum of 16 frames per second to prevent motion from appearing jerky. The human eye is actually better at resolving rapid movements than that number implies. Film projectors also had a shutter that opened and closed up to three times as the film advanced from one frame to the next. The human eye’s flicker fusion frequency (FFF)—the frequency above which individual movements can no longer be resolved—is about 60 Hertz (Hz), or 60 oscillations per second.

Birds have a considerably higher FFF. They can distinguish movements greater than 100Hz. For instance, a fluorescent light oscillating on and off 60 times per second appears continuous to us but looks like a strobe at a disco to a bird.

Newer fluorescent lamps with electronic ballasts—the voltage converter at the base of the lamp—flicker at a very high frequency. However, conventional fluorescent lights flicker at twice the frequency of the electrical supply (60 cycles per second in North America and 50 cycles per second in Europe), resulting in flicker at 120Hz and 100Hz, respectively. In aging bulbs, the brightness of the alternate half-cycles may be of unequal intensity, producing flicker at the frequency of the electrical supply itself.

Disco Duck lighting can interfere with birds’ search for that special someone. A study of captive European starlings found that, under unflickering lights, female starlings consistently preferred males with longer iridescent throat feathers. Under fluorescent lights with a 100Hz flicker, females’ mate choices were erratic. The researchers concluded that flicker may interfere with visual perception or cause low-level stress that makes the birds less choosy.

Raptors that pursue other birds may have the highest FFF because they must fly rapidly while avoiding obstacles and detecting the movements of their prey. Such agility would not be possible if everything blurred together.

Some forms of camouflage, such as the stripes on a zebra or bands on a snake, may rely on a flicker fusion effect of a predator’s vision. If a pattern moves across an animal’s visual field faster than the FFF, the markings may blur to match the background. Alternatively, bands moving at a particular speed could dazzle, distracting attention from a body’s outline and making it difficult to determine its speed and direction.

Individual nerve cells in the brain regions that detect and analyze motion are tuned to motion in specific directions and at specific speeds. Reptiles have fewer nerve cells that respond to motion, compared to birds and humans. Some of the lowest known FFFs are found in lizards in shady, sheltered habitats in which high-speed chases would be a less effective predatory strategy.

Natural selection shaped each organism’s FFF, but it did not prepare humans for the speeds at which we are now capable of traveling. Exposure to a constant speed leads to a reduction in the perceived speed; hence, highway driving gives us a “lead foot.” A reduction in contrast also reduces the perceived speed and makes it seem as if we are going slower when traveling through fog. So, if you get pulled over for speeding, you might try telling the officer about your quirky FFF.

Air Traffic Control

We have a hummingbird feeder hanging from a tree limb. These little critters fly through the tree limbs at a high rate of speed without hitting them. I understand that bats have some kind of bat sonar they use to avoid colliding with anything. But, what do hummingbirds use to keep from running into things?

Hummingbirds have a unique set of anatomical and physiological adaptations that enable particularly complex and rapid flight maneuvers, including the capacity to hover in place better than any other bird.

In general, birds’ deft avoidance of obstacles during flight is facilitated by their eyes’ high FFF. With a high FFF, objects in the surroundings remain distinct instead of blurring together during flight.

Hovering to lap nectar from flowers or a feeder requires another visual adaptation to stabilize flight. Stabilization relies on the optokinetic response, a visual reflex to motion across the retina in which head, eye, or body movements are made in the direction of motion. It links eye and environment to establish a stable base for the execution of behaviors.

The optokinetic response is not unique to hummingbirds—or even birds in general. However, in hummingbirds, a brain region critical for controlling this response (with a name larger than a hummingbird), the pretectal nucleus Lentiformis mesencephali (LM), is considerably larger relative to total brain size than in other birds. The enlarged LM may also facilitate hummingbirds’ unusual ability to fly backward because some of the nerve cells in the hummingbird LM respond exclusively to reverse motion.

In addition to neural adaptations, hummingbirds have a high metabolic rate, a large heart, and modified wing bones and musculature. As a result, hummingbirds can beat their wings faster than other birds and produce force on both the up and down strokes.

Although hummingbirds do not use echolocation (animal sonar) like bats, some birds—including the Oilbird and the Swiftlets—do echolocate. They use echolocation primarily for entering and exiting dimly lit caves where they have their roosting sites. When hunting outside the caves, they rely on vision.

In contrast, insectivorous bats use echolocation to home in on their tiny prey. Echolocating birds can avoid obstacles greater than only about a quarter-inch in diameter, but bats can avoid wires finer than a human hair. In other words, that old rumor about bats getting trapped in your ’do should go the way of the mullet.

Mama Marsupial

How do marsupials, such as kangaroos, which keep their young in their pouches for months, dispose of the waste from the young?

The sight of a kangaroo joey almost its mother’s size climbing back into mom’s pouch makes it clear that humans are not the only species with grown kids reluctant to abandon the comforts of home. If they could talk, kangaroo moms would probably complain about having to clean up after their mama’s joeys.

Kangaroos clean their pouches by sitting back, holding the pouch open with the front paws, and inserting the muzzle into the pouch. Pregnant females begin licking their pouches in earnest before they give birth. They also clean the fur on their stomachs where the tiny newborn will climb to reach the pouch.

As females approach their first breeding season, the pouch grows rapidly and sweat glands within the pouch produce a pigmented, oily substance. The pouch secretions may facilitate the cleaning of the pouch. The secretions and the attention to pouch hygiene protect young marsupials by reducing bacteria in the pouch.

Escargot Explorer

How is it possible for a large snail to place itself on the door of my car? There’s nothing close to the car. For the snail to get there, I think he’d have to come up the side of the tire and under the frame and axel. It appears impossible. Also, why do I find snails on the side of the house, on metal fence posts, and similar places?

The suction created by slime allows snails to crawl upside down, so it could have come from the ground. Alternatively, it might have crawled aboard when your car was parked near bushes. According to a BBC report, some determined snails once got into the habit of crawling up and into mailboxes en masse. Apparently, the snails had taken a liking to the taste of envelopes, possibly for the cellulose they contain.

Snails are most active in damp weather (and rain from sprinkler systems) and at night. In dry conditions, snails retreat into their shells and batten down the hatches. They seal their shell aperture with mucus, which dries to form a sheet called an epiphragm. With the epiphragm to prevent desiccation, snails can remain dormant for months.

Incidentally, the adhesive mucus snails use to form the epiphragm and attach themselves to a surface contains special proteins that link via electrical charges with other molecules in the mucus. Ongoing research into snail mucus may guide biomimetic (mimicking biology) approaches to the design of glues that work in wet environments.

All in the Family

Near the Pacific Ocean at Jaco Beach, Costa Rica, I noticed two types of marine snails in the surf zone. What caught my eye was the speed with which they moved. One snail used a rippling motion of the foot to move across the water film. The other actually flapped its foot, similar to a human swimming the butterfly stroke. Do you know of a mollusk expert who might be able to identify these animals?

Living organisms are classified into a series of hierarchical groups, from broadest to narrowest: domain, kingdom, phylum, class, order, family, genus, and species. Based on this description, Larry Lovell, the collections manager at the Scripps Institution of Oceanography Benthic Invertebrate Collection, and some members of the San Diego Shell Club were able to identify the snail family with reasonable confidence: Olividae.

Lovell and colleagues thought that the genus might be Olivella, Oliva, or Agaronia. It was not possible to narrow the species from this description.

The family Olividae—dubbed Olives by snail enthusiasts—consists of about 400 species. Olives have glossy, olive-shaped shells with a wide variety of markings. They eat dead animal matter as well as live mollusks (other species of snails) and crustaceans (such as shrimp). They seize their prey with the front part of their foot and bring forward the posterior portion of the foot to form a pocket in which they can drag around their prey to snack on.

In addition to predation, the snails’ Olympic swimming abilities may help them scramble to a safe place to park on the beach where the next wave will not fling them too high, according to Don Cadien, a marine biologist with the Sanitation Districts of Los Angeles County, who has studied snails for more than 30 years. The snails must respond to a habitat that changes constantly, as the height of the surf and the angle of the waves vary with the tides.

Shut-Eye for Moby

If whales can go only so long without oxygen, do they sleep?

Whales and dolphins are sometimes seen “logging,” resting at the surface of the water like a floating log. During rest, electroencephalograms (EEGs)—recordings of electrical activity in the brain—detect slow electrical waves on one side of the brain, similar to those detected in humans during deep sleep, whereas the electrical activity in the other side of the brain is similar to that in an awake animal. Therefore, whales and dolphins seem to let one hemisphere of the brain sleep at a time.

No published reports have documented rapid eye movement (REM) sleep in whales or dolphins. Because in humans REM sleep is associated with dreaming, this suggests that whales and dolphins do not dream. They are the only studied mammals that do not have REM sleep.

Another difference is that newborn whales and dolphins do not sleep. Whale and dolphin mothers also go without sleep for substantial periods after the birth of the calf. (Well, maybe they aren’t so different from humans after all.) Over a few months, the calf’s sleep behavior increases to adult levels.

When in the water, fur seals, which may spend weeks without going ashore, have sleep behaviors and brain waves similar to those of dolphins and whales. Surprisingly, fur seals’ sleep changes as soon as they move onto land. Not only do both sides of their brains begin sleeping at the same time, but they also begin to have REM sleep.

Fish Tales

What is the largest species of freshwater fish? How big are they?

Scientists are not absolutely certain because there are many poorly studied fish in very large, deep, or remote bodies of water. Claims about large fish also are prone to error or exaggeration. (You know, the big one that got away!)

Sturgeon are likely the largest fish found in fresh water, although they spend most of their lives in marine environments. Some species of sturgeon that spawn in the rivers of Russia and Europe have reportedly reached 12 to 15 feet and weigh up to 2,000 pounds. Overfishing has made the largest specimens scarce.

For the title of the largest fish species that spends its entire life cycle in fresh water, contenders include the arapaima and goliath catfishes of the Amazon, the Chinese paddlefish, the Mekong giant stingray, and the Mekong giant catfish. Most of these species have become so rare that their maximum size is difficult to determine.

The Guinness Book of World Records lists the Mekong giant catfish as the largest freshwater fish. In 2005, fishermen in northern Thailand caught a 646-pound Mekong giant catfish, the most massive since Thai officials started keeping records in 1981.

Fish-Icles

How can fish live out the winter in 30°F water yet a human can last only 5 minutes? It must have to do with a special oil of some kind inside the fish. But what’s so special about it and how does it do the trick?

In marine mammals, such as seals and whales, fat does play a role—an insulating layer of blubber keeps body heat from escaping. Like us, they are warm-blooded and need to maintain their body temperature within the narrow range in which their enzymes, cells, and organs function best.

Humans also have adaptations that allow us to keep cool when the weather is hot and keep warm when the weather is cold. For example, we shiver and reduce blood flow to the skin so we lose less heat to the environment. However, our ability to thermoregulate has limitations.

As a result, it is not uncommon for people swimming in cold water to perish even if they are close to shore. Immediately upon entering cold water, uncontrollable hyperventilation makes swimming difficult. As the muscles cool, muscle control becomes impaired. Heart attack risk increases as the core body temperature drops and, as nerve cells in the brain lose the ability to communicate, consciousness is lost.

Fish, which are cold-blooded, move to the bottom of ponds or lakes when the water gets too cold, and their metabolism slows dramatically. The metabolism of hibernating mammals also slows dramatically, although, unlike fish, most maintain their body temperatures close to normal. Some mammals, such as the hibernating ground squirrel, allow their body temperatures to fall to just above freezing, a feat scientists still are not certain how they manage to accomplish.

In fresh water, cold-water fish will not freeze to death as long as the lake or pond is of sufficient depth that it does not freeze solid. The situation is different in salt water. The presence of salt in water allows it to get colder than fresh water before it freezes. To survive in water that would make their cousins from tropical and temperate regions into frozen fish sticks, Arctic and Antarctic fish have developed antifreeze molecules.

The antifreeze molecules are proteins that bind to tiny ice crystals in the blood of the fish and prevent the ice crystals from getting bigger. Exactly how the proteins do this is under investigation. It’s not just a matter of academic interest. These proteins are hundreds of times more effective than chemical antifreezes at the same concentration.

They have potential applications as nonpolluting deicing agents for airplanes, or in preventing ice crystals from damaging tissues and organs that are being cryopreserved.