IELTS Academic Reading Practice Test 424

The vaquita is a porpoise that lives nowhere on earth except the northern end of the Gulf of California, between the Mexican mainland and Baja California. Its name is Spanish for 'little cow', and it is the smallest of all whales, dolphins and porpoises: adults rarely exceed 1.5 metres in length. Its range is one of the smallest of any marine mammal. It is distinguished by dark patches around its eyes and lips and by a dorsal fin that is taller, in proportion to its body, than those of its relatives. Vaquitas are shy and inconspicuous, surfacing briefly and avoiding boats, and the species remained unknown to science until 1958, when it was described from skulls found on a beach.

The animal is confined to a small area of shallow, murky water, mostly less than 50 metres deep, where tides stir up sediment and visibility is poor. The water is often turbid, and sight is of limited use. It feeds on small fish, squid and crustaceans, finding them by echolocation: it produces rapid clicks and interprets the returning echoes. How it perceives fishing nets is a crucial question. Like other porpoises, the vaquita uses very high-pitched clicks, and some researchers suspect that such signals are poorly reflected by the thin filaments of nylon nets.

That suspicion matters because nets are almost certainly the cause of the species' collapse. Gillnets are walls of fine mesh that trap fish behind the gills, and they are extremely effective; a porpoise that swims into one becomes entangled and, being an air-breathing mammal, drowns within minutes. One type of net in particular has driven the decline. The totoaba is a large fish that is itself endangered, but its swim bladder is highly prized in parts of East Asia as a delicacy and in traditional medicine, and a single bladder can be worth more than a fisher earns in a year. Nets set illegally for totoaba kill vaquitas in disproportionate numbers.

The figures are stark. A survey in 1997 estimated that nearly 600 vaquitas remained. By 2015 the estimate had fallen to about 60, and by 2018 to about 19. Since then acoustic monitoring, which counts the distinctive clicks picked up by underwater detectors, has suggested a population of roughly ten animals, though estimating so few is extremely difficult. On any of these figures the vaquita is the most endangered marine mammal in the world.

Mexico has taken a series of measures. A biosphere reserve covering the upper gulf was established in 1993, and in 2015 the government banned gillnets across most of the vaquita's range for two years, paying compensation to fishers who surrendered their permits. In 2017 the ban was made permanent, and further payments were offered to encourage the use of alternative gear. Enforcement, however, has always been the weak point. The area is large, patrols are few, and a confiscated net can be replaced within days; abandoned gear continues to trap animals long after it has been lost.

A more drastic idea was tested in 2017. An international project attempted to catch several vaquitas and keep them in a floating sea pen where they might breed in safety. The operation was called off after a female died soon after being brought to the surface, apparently of stress, and conservationists concluded that removing the remaining animals was too risky. Attention returned to the water: to developing nets that catch shrimp and fish without drowning porpoises, and to persuading fishers to use them. Several designs have been tested, but they cost more, catch less or demand unfamiliar techniques, and take-up has been limited.

Genetics adds a further complication, though not necessarily a gloomy one. With so few individuals left, inbreeding and the loss of diversity would normally be expected to weaken the species' capacity to recover. Studies of its genome, however, indicate that the vaquita has existed in small numbers for a very long time and carries less harmful variation than its present plight might suggest. On this view the species is not doomed by its genes, and if the nets were removed it could in principle begin to increase. The qualification is that a population of ten is vulnerable to chance events as well as to human ones.

The human dimension is equally difficult. Two small ports on the gulf depend on fishing, and many families regard restrictions imposed from the capital as a threat to their livelihood. Compensation schemes have been criticised for delays and for failing to reach crew members who do not hold permits. Tourism offers only a partial substitute, since a vaquita is hardly ever seen; visitors come instead for sport fishing, which itself depends on the health of the ecosystem. Conservationists argue that the only durable solution gives local communities a stake in the survival of the porpoise.

The scientific consensus is bleak and simple. The International Committee for the Recovery of the Vaquita, a panel of experts that advises the Mexican government, has repeatedly recommended that all gillnets be removed from the species' range and that the ban be enforced. Without that, the committee has warned, the decline will continue whatever else is done. Whether the remaining animals can hold on long enough for enforcement to become effective is now the only question that matters.

On autumn and winter evenings, in parts of Britain and northern Europe, starlings gather in flocks that can number tens of thousands and perform the swirling aerial displays known as murmurations. The birds arrive from feeding areas over an hour or so, joining in groups that merge into a single mass, which twists, folds and stretches above the roost before dropping almost at once into the trees or onto the roofs where the flock will spend the night. The display lasts only a few minutes, but it is one of the most conspicuous examples of collective behaviour in the animal kingdom.

Starlings are unremarkable birds for most of the year; it is the flocks that people notice. They roost communally in winter, sometimes in town centres where buildings hold the warmth of the day. Huddling together conserves heat on cold nights, and a communal roost may also offer some protection from predators. In Britain the species has declined sharply since the 1970s and is now on the red list of birds of conservation concern. The murmurations that draw spectators to seaside piers are thus a sign of a bird in trouble as much as a spectacle.

Explaining the behaviour has occupied biologists for more than a century. The obvious suggestion is that a large flock confuses predators: a peregrine falcon diving into a dense mass of thousands of birds finds it hard to fix on one target. A second proposal is that each bird's individual risk is diluted when there are many others nearby. Both ideas are plausible and hard to separate, and neither explains why the flock performs such elaborate movements rather than simply clustering tightly. It has also been suggested that birds save energy by exploiting the rising air created by the wings of those ahead, though that idea has attracted little support.

The obstacle has always been measurement. To understand how a flock works you need to know where each bird is and what it does, and a murmuration is a cloud of small, fast-moving objects several hundred metres away, usually in the half-light of dusk. A single photograph flattens the flock, because birds that appear to be neighbours may be far apart in depth. Progress came when researchers in Rome turned pairs of cameras on flocks wheeling over the city and used the slight difference between the two images to calculate the position of every bird in three dimensions, relying on the principle that gives humans stereoscopic vision.

The results, published in 2008, were unexpected. It had been assumed that each bird monitored its neighbours within a fixed distance and adjusted its flight to theirs. Instead the analysis showed that a starling responds to a fixed number of neighbours, about seven, regardless of how far away they happen to be. In a dense part of the flock those seven may be within a metre; where birds are more spread out they may be several metres away. Because the rule is numerical rather than spatial, information can pass through a flock of any size at much the same speed.

Simulations support this account. Computers can be filled with virtual birds, each following a few simple rules: keep a certain distance from neighbours, match their direction, and move towards them if too far apart. Such models reproduce the characteristic shapes of real murmurations, without any bird knowing what the flock as a whole is doing. Work by modellers in the Netherlands has shown that these simulated flocks hover at the edge of order, a state in which a change of direction by one bird can spread across the entire flock rather than fading away.

The same mathematics describes physical systems at a critical point, such as a magnet about to lose its magnetism, where a small local change can have effects far away. Flocks appear to sit close to that condition. Measurements of real murmurations have found that the movements of birds many metres apart are correlated, so that a turn by one individual is reflected, faintly, by others at the opposite edge of the flock, and the change passes between neighbours in a fraction of a second. It remains unclear whether starlings gain any advantage from this scale-free behaviour or whether it is simply what falls out of the rules they follow.

Predators are still the focus of most explanations. Filming attacks by peregrine falcons has shown that a flock responds by splitting and re-forming, and that the birds do not simply flee in one direction. Some studies suggest that the wave of turning that runs through a flock can travel faster than a falcon can approach, though others dispute how much protection this offers. A quite different suggestion, that birds follow their neighbours to find good feeding sites, has less support, since the flock disperses at dawn in many directions and not towards a single place.

What remains uncertain is why the display should be so conspicuous. If the purpose were merely to avoid being eaten, a tight, silent, fast-moving ball would presumably serve; instead starlings produce something slow, elaborate and visible from a great distance. Perhaps the answer is a mixture of confusion, dilution and the sheer difficulty for a predator of tracking one target inside a moving object. The honest position is that the function of the murmuration, unlike its mechanics, is still not settled.

Ask visitors to a national park what they paid to get in and the answers vary enormously. In the United States most of the best-known parks charge at the entrance, usually by the vehicle, and the ticket is valid for several days. In Britain nothing is charged for walking into the hills of the Lake District or Snowdonia, though almost every car park has a machine. In parts of East and southern Africa, foreign visitors pay substantial daily fees while nationals pay far less or nothing at all. Behind these differences lies a genuinely difficult question: who should pay for the conservation and enjoyment of land that is held, in principle, on behalf of everyone?

The national park idea is usually traced to Yellowstone, set aside by the United States in 1872, and the principle behind it was that landscapes of outstanding value should be preserved for the benefit and enjoyment of the people rather than for a court or a private owner. In the century that followed, similar arrangements spread: land was bought or donated and then held in public hands, usually by an agency with a legal duty to conserve it. For much of the twentieth century such parks were paid for out of general taxation, on the understanding that their worth to a nation could not be captured by a ticket office.

Advocates of charging point to an awkward financial fact. The demands on park authorities have grown while their budgets have not: roads, trails and visitor centres built decades ago now need repair, and the cost of looking after wildlife and managing congestion falls on the same fixed purse. A fee provides income that a finance ministry cannot easily redirect elsewhere, and it ties the cost of a visit to the wear that the visit causes. Visitors, on this view, should contribute towards the paths they walk on, just as they pay for a museum or a train fare.

Economists make a related point in the language of prices. A park that is free to enter but expensive to maintain is a resource that is overused, because each visitor bears none of the cost they impose on others. A charge rations scarce capacity, and it can be varied by season or time of day to spread demand. The objection is that the sums involved are trivial next to the cost of getting there: a family that has driven three hundred kilometres will not turn back because of a modest entrance fee, so the effect on numbers may be far smaller than theory suggests.

There is also a question of fairness. Charges at the gate are regressive, in the sense that they take a larger share of a poor household's budget than of a rich one's, and visits to remote landscapes already require a car and free time. Where a park was created on land from which communities were once removed, charging their descendants to enter can be politically explosive. A fee may also deter precisely the people whose taxes support the park and who visit it least often, which is a strange outcome for an institution that claims to belong to the whole nation.

A further objection is that citizens already pay twice. Parks maintained from public funds belong to everybody, and a second charge at the boundary can weaken the argument for public money: if visitors can be made to pay, the reasoning goes, why should anyone else contribute? Once a park has learned to live on ticket income, the case for taxation is harder to make, and the people who never visit but value the place's existence lose their claim on it. The danger is real.

Charging also changes the incentives of the institution that collects the money. A park whose budget depends on visitor numbers has a reason to attract more of them, exactly when congestion is the problem it is trying to solve. Critics of commercialisation describe a drift from conservation towards entertainment: cafes, gift shops and adventure activities, with decisions taken with an eye on revenue rather than on ecology. The landscape risks becoming a backdrop, and the wildlife a supporting attraction.

Other instruments exist. Charging for parking captures many of the same visitors while leaving access on foot, by bicycle or by bus free, which is why it is common in Britain. Levies on hotels, car-hire firms and tour operators spread the cost across the tourist economy, and several countries raise money this way. Permits and booking systems limit numbers at the most fragile sites, and in some parks they have replaced the informal queue at a car park gate. Voluntary donations, lottery funds and membership schemes all help, though none is reliable enough to replace a settled budget.

My own view is that a modest charge at the busiest sites is defensible, provided that the money is earmarked for conservation and that local residents, schools and those arriving without a car are exempt. But it would be a mistake to regard fees as a solution to the underlying problem. The sums raised are small compared with what parks need. More importantly, a nation's finest landscapes are a common inheritance rather than a service sold by the hour. A park is not a business whose success is measured by visitor numbers; it is a trust held for people who have not yet been born.