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Reading Test 52
Animal Camouflage
A
The theory of natural selection, proposed by Charles Darwin almost 150 years ago, hypothesizes that organisms with traits that give them a survival advantage tend to live longer and produce more offspring. Over many thousands of years of evolution, those beneficial characteristics dominate the gene pool. Animals that use camouflage to conceal themselves from their enemies, predator and prey alike, provide a classic example of natural selection at work. Creatures with some type of protective coloring pass along the genes responsible, with each generation fine tuning them along the way, eventually providing the most effective coloring for their environment and lifestyle. Scientists have described four types of camouflage that animals use: background matching, disruptive coloration, countershading, and mimicry.
B
From dirt-colored chipmunks and gophers to leaf-green praying mantises and tree frogs to ocean gray mackerel and sharks, all sorts of wildlife use background matching, also known as crypsis, to blend in with their surroundings. Some animals have the ability to alter their coloring as their environment changes seasonally or as they change locations. The arctic ox and the snowshoe hare both have white winter fur that matches the snow and ice around them, but a brown pelt in warmer weather blends in with their woodland environs. Some reptiles and fish can alter their surface appearances instantly as they move from place to place. The green anole lizard changes from green to brown as it travels among leaves and branches, whereas the flounder and other types of flatfish are able to match not just the color but also the silty or mottled sandy texture of the ocean floor beneath them.
C
Most animals, though, cannot change their appearance so easily. Because background matching works only for a specific setting and often requires animals to remain motionless for long periods, a somewhat more effective strategy involves having a camouflage that works on many backgrounds, blending in with all, but not perfectly matching any of them.
D
Disruptive coloration uses a pattern such as stripes or spots to disrupt the body outline. The pattern breaks up the contour of the animal’s body, confusing observers and making it difficult to distinguish an individual shape. Colors with more contrast, like a tiger’s stripes, tend to increase the disruptive effect. This type of camouflage works well for animals that travel in herds. It helps zebras blend in not so much with their background as with each other. Their major predator, the lion, sees a mass of moving stripes and has trouble targeting a specific animal. A single zebra, on the other hand, may use background matching when hiding in tall grass, where it’s black and white stripes merge with the green and yellow stalks. The different colors of the grasses and zebras are no help to a lion, which is color-blind.
E
Animals with counter-shading typically have a dark backside and a light belly, which affect an onlooker’s perception of their three-dimensional appearance and help decrease their visibility in sunlight. Counter-shading also can create a more uniformly dark appearance, presenting an apparent lack of depth. Caterpillars make good use of this effect, which gives them a flat look that blends in with tree bark.
F
Counter-shading is useful to birds and marine animals that are typically seen against a light environment from below and against dark surroundings from above. Predatory birds like hawks take advantage of it to conceal themselves from the small birds and rodents they hunt. While in flight, a dark back absorbs the sunlight above them and the light underside reflects the light below, diminishing telltale shadows that might give them away. On the ground or in a tree, their mottled brown feathers blend in with branches and leaves. Penguins also use counter-shading. Their white chests and black backs stand out on land but disappear in water where penguins spend most of their time. They are almost invisible to an observer looking down into dark water, while a creature in deeper water looking up sees a splash of white that looks like a beam of sunlight.
G
Mimicry, or masquerading, works not by hiding a creature but by making it appear to be something else. Walking stick insects are virtually indistinguishable from twigs, and katydids look so much like green leaves that leaf-eating insects have been observed trying to chew on them.
H
A type of mimicry known as aposematism involves masquerading as an animal that is undesirable or even dangerous. Predators bypass the foul-tasting monarch butterfly, but they also avoid the tasty looking viceroy butterfly. Coral snake impersonators, like the harmless scarlet snake, have the same red, black, and yellow bands but in a different order: black, yellow, red, yellow on the coral snake and red, black, yellow, black on the scarlet snake. Different types of wasps use aposematism to scare off predators; some species have a big spot on each wing to mimic the eyes of a large animal, while the hawk moth caterpillar has a pattern on its rear that looks like a snake head.
I
Some predators use what is known as aggressive mimicry to disguise themselves as something harmless so they can catch prey off guard. Small animals are not afraid of turkey vultures, which are scavengers, not predators. So when a similarly zone-tailed hawk flies with a group of turkey vultures, it has an easy time locating and zeroing in on its living prey.
J
No single type of camouflage works best in all situations, and many animals use more than one technique to enhance their ability to avoid detection by predators and prey alike.
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Bird Migration
A.
Birds’ various distinctive design elements allow them to pull off such astounding endurance feats. They have hollow, light-weight bones, intricately patterned feathers that provide thrust and lift for swift flight, navigation systems that are far superior to those created by humans, and a clever heat-conserving structure that, among other things, enables all blood circulation below layers of warm, water-resistant plumage, making them capable of surviving in the harshest climates. Their respiratory systems must function effectively during prolonged altitude flights, thus they have an oxygen extraction system from their lungs that is significantly superior to that of any other mammal. Their bodies can build up significant amounts of fat throughout the later stages of the summer breeding period, when food is abundant, to give them enough energy for their lengthy migratory trips.
B.
Finding enough food during the winter, when it is scarce, is the primary driver behind bird migration. This is especially true for birds that breed in the Northern Hemisphere’s temperate and arctic regions, where there is an abundance of food throughout the brief growing season. Many species must move when food is sparse since they can withstand frigid conditions if there is plenty of it. But intriguing issues still exist.
C.
Many birds go farther than would be necessary to locate food and favourable weather, which is a curious reality. Nobody is sure why British swallows don’t travel thousands of miles further to their preferred winter habitat in South Africa’s Cape Province, despite the fact that they could certainly make it through the winter in equatorial Africa. The huge migrations performed by shorebirds that breed close to the poles and arctic terms that hunt on mudflats are still unresolved. In general, migrating species spend their winters farther south the further north they breed. This requires an annual round trip of 25,000 kilometres for arctic terns. All of these individuals, however, fly over other regions of what appears to be ideal habitat spanning two hemispheres en route to their eventual destination in remote southern latitudes. Whilst we may not entirely comprehend the reasons why birds visit certain locations, we can nevertheless be in awe of their accomplishments.
D.
One of the biggest mysteries is how young birds, who don’t have parental supervision, can find the typical wintering locations. Fewer people travel with young children, and occasionally kids don’t even know what their parents seem like. The cuckoo, which lays its eggs in the nest of another species and never sees its young again, is a well-known example. It is incredible to think that after being nurtured by its host species, the young cuckoo migrates to its original tropical wintering habitats before returning alone to northern Europe the next season to seek a mate among its kind. The logical conclusion is that it receives from its parents an innate ability to navigate and find its way, as well as a mental image of another cuckoo. However, no one has the foggiest notion as to how this is even conceivable.
E.
There is growing proof that birds utilise the sun and stars’ positions as compass directions. Additionally, they appear to be able to sense the earth’s magnetic field, which is possibly because their brains contain tiny magnetite crystals. However, accurate navigation also necessitates a sense of place and time, particularly when being lost. Birds can still quickly return to their nesting locations even after travelling thousands of kilometres over an alien terrain, according to experiments. Such extraordinary abilities are the result of the combination of a number of complex stimuli, such as an innate map of the night sky and the pull of the earth’s magnetic field. Unknown is how the birds employ their “instruments,” but one thing is certain: their sensory awareness of the environment is superior to ours. The majority of birds migrate at night and follow the position of the setting sun. Nevertheless, in addition to witnessing the sun set, they also appear to see the plane of polarised light that it produces, which serves to calibrate their compass. Other advantages of nighttime travel exist. Predators who hunt during the daylight hours are avoided, and there is less of the probability of being dehydrated from extended flight under hot, sunny sky. Additionally, the air is often calmer and cooler at night, which is perfect for stable, long-distance flight.
F.
All journeys, however, carry a significant amount of danger, and leaving on time is a skill in itself for arriving safely. This calls for using precise weather forecasts and taking advantage of suitable winds. Birds are skilled at both, and laboratory experiments have revealed that some of them can even detect the slight variation in barometric pressure between the room’s floor and ceiling. Birds frequently respond to weather fluctuations before there is any outward evidence of them. Lapwings, which consume grassland, travel from the Netherlands to the British Isles, France, and Spain as a cold front approaches. The birds might go hungry if the ground freezes. However, they make their way back to Holland before a thaw because of a pressure change that predicted an improvement in the weather.
G.
The day prior a letter announcing its release, a Welsh Manx shearwater that had been transported to America and freed was found returned in its burrow on Skokholm Island off the coast of Pembrokeshire! On the other hand, every autumn, a few North American birds are carried across the Atlantic by strong westerly tailwinds. They certainly make it to Europe without incident, however there is compelling evidence that some of them return to North America the following spring, having likely spent the winter with European migrants in warm African climates.
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Malaria Combat in Italy
A
Mal-aria. Bad air. Even the word is Italian, and this horrible disease marked the life of those in the peninsula for thousands of years. Giuseppe Garibaldi’s wife died of the disease, as did the country’s first prime minister, Cavour, in 1861. Yet by 1962, Italy was officially declared malaria-free, and it has remained so ever since. Frank Snowden’s study of this success story is a remarkable piece of historical work. Original, crystal-clear, analytical and passionate, Snowden (who has previously written about Boccaccio) takes us to areas historians have rarely visited before.
Everybody now knows that malaria is carried by mosquitoes. Malaria has always been the subject of research for medical practitioners from time immemorial. However, many ancient texts, especially medical literature, mention of various aspects of malaria and even of its possible link with mosquitoes and insects. Early man, confronting the manifestations of malaria, attributed the fevers to supernatural influences: evil spirits, angered deities, or the black magic of sorcerers. But in the 19th century, most experts believed that the disease was not produced by unclean air (‘miasma’ or ‘poisoning of the air’). Two Americans, Josiah Clark Nott and Lewis Daniel Beauperthuy, echoed Crawford’s ideas. Nott in his essay “Yellow Fever Contrasted with Bilious Fever,” published in 1850, dismissed the miasma theory as worthless, arguing that microscopic insects somehow transmitted by mosquitoes caused both malaria and yellow fever. Others made a link between swamps, water and malaria, but did not make the further leap towards insects. The consequences of these theories were that little was done to combat the disease before the end of the century. Things became so bad that 11m Italians (from a total population of 25m) were “permanently at risk”. In malarial zones, the life expectancy of land workers was a terrifying 22.5 years. Those who escaped death were weakened or suffered from splenomegaly – a “painful enlargement of the spleen” and a “lifeless stare”. The economic impact of the disease was immense. Epidemics were blamed on southern Italians, given the widespread belief that malaria was hereditary. In the 1880s, such theories began to collapse as the dreaded mosquito was identified as the real culprit.
C
Italian scientists, drawing on the pioneering work of French doctor Alphonse Laveran, were able to predict the cycle of fever but it was an Rome that further key discoveries were made. Giovanni Battista Grassi, a naturalist, found that a particular type of mosquito was the carrier of malaria. By experimenting on healthy volunteers (mosquitoes were released into rooms where they drank the blood of the human guinea pigs), Grassi was able to make the direct link between the insects (all females of a certain kind) and the disease. Soon, doctors and scientists made another startling discovery: the mosquitoes themselves were also infected and not mere carriers. Every year, during mosquito season, malarial blood was moved around the population by the insects. Definitive proof of these new theories was obtained after an extraordinary series of experiments in Italy, where healthy people were introduced into malarial zones but kept free of mosquito bites – and remained well. The new Italian state had the necessary information to tackle the disease.
D
A complicated approach was adopted, which made use of quinine – a drug obtained from tree bark which had long been used to combat fever but was now seen as a crucial part of the war on malaria. Italy introduced a quinine law and a quinine tax in 1904, and the drug was administered to large numbers of rural workers. Despite its often terrible side-effects (the headaches produced were known as the “quinine-buzz”), the drug was successful in limiting the spread of the disease, and in breaking cycles of infection. In addition, Italy set up rural health centres and invested heavily in education programmes. Malaria, as Snowden shows, was not just a medical problem, but a social and regional issue, and could only be defeated through multi-layered strategies. Politics was itself transformed by the anti-malarial campaigns.
E
We originally decided to give quinine to all those in certain regions – even healthy people; peasants were often suspicious of the medicine being forced upon them. Doctors were sometimes met with hostility and refusal, and many were dubbed “poisoners”. Despite these problems, the strategy was hugely successful. Deaths from malaria fell by some 80% in the first decade of the 20th century and some areas escaped altogether from the scourge of the disease.
F
Shamefully, the Italian malaria expert Alberto Missiroli had a role to play in the disaster: he did not distribute quinine, despite being well aware of the epidemic to come. Snowden claims that Missiroli was already preparing a new strategy – with the support of the US Rockefeller Foundation – using a new pesticide, DDT. Missiroli allowed the epidemic to spread, in order to create the ideal conditions for a massive, and lucrative, human experiment. Fifty-five thousand cases of malaria were recorded in the province of Littoria alone in 1944. It is estimated that more than a third of those in the affected area contracted the disease. Thousands, nobody knows how many, died.
G
With the war over, the US government and the Rockefeller Foundation were free to experiment. DDT was sprayed from the air and 3m Italians had their bodies covered with the chemical. The effects were dramatic, and nobody really could have predicted this outcome. By 1962, malaria was more or less gone from the whole peninsula. The last cases were noted in a poor region of Sicily. One of the final victims to die of the disease in Italy was the popular cyclist, Fausto Coppi. He had contracted malaria in Africa in 1960, and the failure of doctors in the north of Italy to spot the disease was a sign of the times. A few decades earlier, they would have immediately noticed the tell-tale signs; it was later claimed that a small dose of quinine would have saved his life.
H
As there are still more than 1m deaths every year from malaria worldwide, Snowden’s book also has contemporary relevance. This is a disease that affects every level of the societies where it is rampant. As Snowden writes: “In Italy, malaria undermined agricultural productivity, decimated the army, destroyed communities and left families impoverished.” The economic miracle of the 50s and 60s which made Italy into a modern industrial nation would not have been possible without the eradication of malaria. Moreover, this book convincingly argues that the disease was “an integral part of the big picture of modern Italian history”. This magnificent study, beautifully written and impeccably documented, deserves an audience beyond specialists in history, or in Italy. It also provides us with “a message of hope for a world struggling with the great present-day medical emergency”.
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