IELTS Academic Reading Practice Test 408

The kakapo, Strigops habroptilus, is the most unusual of parrots. It is the only parrot that cannot fly, the heaviest parrot in the world, and one of very few that are nocturnal. Adults are mottled moss green, barred with yellow and black, so that a bird standing still among dense scrub is extremely difficult to see. They have an owl-like disc of feathers around the face and large forward-facing eyes. Males are much bigger than females and may weigh close to four kilograms.

Kakapo evolved in a country that had almost no land mammals, and nothing hunted birds by scent on the forest floor. The bird's response to danger was not to fly but to freeze. At an unfamiliar sound a kakapo stops and stays motionless. That was excellent protection against a hunting bird that relies on movement, and useless against a cat or a stoat. Because escape by flight was unnecessary, the species lost much of the keel to which flight muscles are attached, and its wings are now used mainly for balance and for slowing a descent from a tree.

Kakapo breed only in years when the rimu, a tall native conifer, produces a heavy crop of fruit — an event that occurs every two to five years. In such a season males gather at traditional sites on ridges, where each digs a shallow bowl and sits in it, inflating a sac in the chest and producing a low boom that carries for several kilometres. Females visit these sites and mate, then raise the chicks entirely alone. One to four eggs are laid in a burrow or beneath tree roots, and the female incubates them. The male contributes nothing beyond his call.

The first Polynesian settlers reached New Zealand in the thirteenth century, bringing the kiore, or Pacific rat, and hunting the birds for meat and feathers. European settlers later introduced cats, stoats, ferrets and possums, all of which take eggs, chicks or adults. Kakapo are long-lived and slow to reproduce. Early naturalists described the bird as common in parts of the South Island, but by the beginning of the twentieth century it had disappeared from most of that range.

One of the first people to attempt a rescue was Richard Henry, a self-taught naturalist who lived on the shore of Lake Te Anau. In the 1890s he carried kakapo and kiwi by boat to Resolution Island, which he believed predators could not reach. Then stoats crossed the water, and within a short time the island's flightless birds had gone. Henry's effort is remembered as a brave failure, but it established the principle on which kakapo conservation still depends: the birds survive only where there are no mammalian predators.

For most of the twentieth century the kakapo seemed to be slipping away. Sightings became rare and were often unconfirmed, and by the 1970s many biologists assumed that the species was extinct. Then, in 1977, a population was found on Stewart Island. The birds were living in scrub and forest that cats and rats had already reached. A decision was taken to move every bird that could be caught to islands from which predators could be kept out.

Such islands now hold almost the entire population. The main population lives on Whenua Hou, or Codfish Island, a small island off Stewart Island that has been cleared of introduced predators. A second population was established on Anchor Island, in Dusky Sound. Quarantine is strict: visitors must clean their equipment, because a single rat reaching one of these islands could undo decades of work.

Conservation now depends heavily on technology. Every kakapo carries a transmitter, and a network of receivers reports the position and activity of each bird, so that rangers know when a female has begun to nest. Nests are watched with cameras and with sensors that record the temperature of the eggs. When the rimu crop looks promising and a female lays, staff may remove her eggs for artificial incubation, which often prompts her to lay again; the chicks are reared by hand and returned to the island. Supplementary food stations allow birds to be weighed.

None of this removes the underlying problem, which is that the population is tiny and closely related. Low genetic diversity leaves the species vulnerable to disease, and every breeding season is a nervous one: an outbreak of illness at the wrong moment could kill a large share of the world's kakapo within weeks. The birds are also ageing. Many of those that founded the present population are still breeding, but they will not do so indefinitely, and each egg that fails to hatch now removes a larger fraction of the species' future than it once would.

To Ngāi Tahu, the iwi whose territory includes Whenua Hou, the kakapo is a taonga, a treasure, and the recovery programme is run as a partnership with the tribe. In 2023 a small group was moved to a fenced sanctuary on the North Island as a trial, the first kakapo to live on the mainland for decades. National projects to remove possums, rats and stoats by 2050 offer hope, but nobody expects kakapo to live freely on the unfenced mainland within the lifetime of the birds now living. For the foreseeable future the bird's survival will depend on small islands, transmitters and people.

A seabird may spend months at sea without ever encountering fresh water. Albatrosses, petrels, gulls and penguins drink sea water, which contains roughly three times as much salt as their own body fluids. For a mammal, including a human being, this would be worse than drinking nothing, because the water needed to flush out the surplus salt would exceed the water gained. Yet seabirds evidently cope, and the reason lies in a structure in the head that has no equivalent in mammals.

Bird kidneys are not the answer. Compared with those of mammals, they are poor at concentrating waste: the urine a bird produces can be little saltier than its blood, so the kidney can remove only a limited amount of salt in a given volume of water.

Mammals can produce urine far more concentrated than their blood, and it is this ability, absent in birds, that allows a camel or a kangaroo rat to survive on very little water. A bird relying on its kidneys alone could not dispose of the salt in a glass of sea water without losing more water than it had swallowed. The organs that make sea water drinkable are instead glands that empty into the nose.

Seabirds have a pair of salt glands, also called nasal glands, lying in sockets above the eyes. Each is a compact mass of many hundreds of tiny tubes, supplied with blood at a remarkable rate. The fluid they produce passes down ducts into the nasal cavity and out through the nostrils, and in most species it leaves the body as drops at the tip of the bill, which the bird shakes away. In the petrels and albatrosses, whose nostrils are enclosed in tubes on top of the bill, the brine trickles along a groove to the same destination.

The chemistry is what makes the system work. In the late 1950s the physiologist Knut Schmidt-Nielsen and his colleagues established that the glands, and not the kidneys, were the source of the salty fluid, and that secretion could continue for hours. Analysis showed that its sodium concentration can exceed that of sea water, in some species by as much as a factor of two. Because each drop carries away more salt than the water it contains, the bird ends the process with a net gain of water. The gland, in effect, desalinates by removing salt rather than by producing pure water.

The gland is not permanently in action. It switches on within minutes of a salt load, when the blood supply to it increases sharply, and it can enlarge over days or weeks if a bird is kept on a salty diet; when the bird returns to fresh water it shrinks again. This flexibility is itself revealing. Ducks and other birds of freshwater habitats usually possess small glands, although these too can grow if the birds are gradually given saltier water. Penguins and tubenoses, by contrast, have glands that can be very large.

Secretion is expensive. Pushing sodium ions out of the blood against a concentration gradient requires energy, and while it is working the gland consumes oxygen at a high rate. Measurements suggest that in a bird actively disposing of salt the gland can account for a significant share of its resting metabolism, although estimates vary. This cost helps to explain why seabirds do not drink sea water continuously. Fish, squid and krill contain far less salt than the sea does, and a bird that feeds well may need to use its glands hardly at all.

Other animals have arrived at the same solution. Sea turtles have glands near the eyes that shed a salty fluid sometimes mistaken for tears, marine iguanas expel the excess through the nose with a forceful sneeze, and crocodiles have salt-excreting glands on the tongue. Among plants, too, glands on the leaves allow species growing near the shore to shed the salt spray that would otherwise poison their tissues. The repeated evolution of the trick suggests that it is one of the few ways of life available to an animal that must live in a salty environment.

Several questions remain open. The proteins that move sodium across the gland's cells have been identified, but how their activity is adjusted from minute to minute is not fully understood, and neither is the way the brain registers that the body has taken in too much salt. Why some species have much larger glands than others with similar diets is also unexplained. Nor is it clear how quickly a young bird's glands become fully functional, or how much of the water a seabird needs comes from its food rather than from the sea.

What is clear is that the gland is only part of a water economy. Many seabirds obtain most of what they need from their food, and the breakdown of fat in particular releases water as it is oxidised; birds feeding on oily prey may go for days without drinking. The salt gland matters most when a bird has eaten unusually salty food, or has had no choice but to drink from the sea. It is a remarkable piece of machinery, but it is a supplement to a way of life rather than a licence to drink salt water freely.

Few questions in conservation are as uncomfortable as what to do with an animal that has nowhere to go. Every year zoos breed hundreds of species that are extinct, or nearly extinct, in the wild: frogs that died out when a fungus swept through Central American streams, antelope that vanished from the Sahel, a Hawaiian crow that now survives only in breeding centres. Some conservation biologists maintain that breeding such animals is a duty, and that a species kept alive in captivity may one day be returned to the wild. Others argue that a breeding programme with no release date is not conservation at all but a form of long-term captivity, sustained by visitors' affection for animals that will never leave. This article asks which of them is right.

The case for keeping a captive population is straightforward. A zoo can hold a genetic reserve that no longer exists anywhere else, and the techniques involved — studbooks, careful pairing, artificial insemination, the freezing of embryos and sperm — have improved enormously in the past three decades. Such a population is also unusually well documented, since every animal's parentage is recorded. Some zoo directors argue that the cost of maintaining such a reserve is modest compared with the cost of losing the species entirely, and that a captive population can help to pay for field work: visitors who come to see a rare antelope also pay for the wardens who protect its remaining habitat. On this view, captivity is not an alternative to conservation but a part of it.

Reintroductions do happen, and some have worked. Scimitar-horned oryx, extinct in the wild by the end of the twentieth century, have been returned to the grasslands of Chad, where captive-bred animals have established themselves and bred. Przewalski's horse, which survived only in zoos for decades, now runs again on the steppes of Mongolia. California condors, reduced to a couple of dozen birds, have been released in Arizona and California, and the population is slowly growing. These are real achievements, but each depended on a habitat that still existed, or could be restored, and on a local commitment to protect the animals once they were free.

For other species no such place exists, at least for now. The Panamanian golden frog is extinct in the wild, wiped out by a fungal disease that persists in the streams it once inhabited; releasing frogs today would simply expose them to the same infection. Habitat destruction makes the point even more sharply: a forest that has been fenced, drained and planted with crops cannot be remade by returning the animals that once lived in it. In such cases the captive population is a museum of a species, kept alive for reasons that are partly scientific and partly sentimental, and its members may be bred indefinitely without contributing to the recovery of anything outside the zoo. Conservationists call this reliance on captivity, and it is hard to argue that a species held this way is recovering.

The welfare argument is harder to dismiss. Large carnivores, elephants and primates kept in confined spaces frequently develop repetitive behaviour — pacing, swaying, over-grooming — that indicates psychological stress, and many zoo animals receive drugs for conditions rarely seen in the wild. Zoos now invest heavily in enclosure design and in what they call environmental enrichment, and the standards of the best institutions are high. Modern enclosures attempt to reproduce the complexity of a wild habitat, with mixed planting, varied surfaces and feeding tasks that take time to complete. Yet a space large enough for an elephant is seldom large enough for a population of elephants, and the social life of a herd cannot easily be reproduced in a few hectares of enclosure. An animal that will never be released must live its whole life in such conditions, which raises the standard those conditions must meet.

Then there is the question of money. Maintaining a genetically viable group of a large mammal is expensive: veterinary care, breeding programmes and the buildings that house them consume millions. The same sum spent on protecting forest or on paying local rangers might save far more species, including some that will never attract a crowd. Donors, moreover, give to animals with faces rather than to ecosystems. Zoos answer, reasonably, that the money is not transferable, since nobody leaves a legacy for a beetle. But the argument cuts both ways, because it also means that the species chosen for breeding are chosen for their power to attract visitors rather than for their need.

My own view is that a breeding programme is justified when it serves a realistic plan for release, when the welfare of the animals is demonstrably good, and when the public is told the truth about the animal's prospects. Where those conditions hold, keeping a species in captivity is a reasonable use of resources, and the successes of the past three decades show that it can work. Where they do not — where there is no habitat, no release plan and no honest account of the future — a zoo is keeping animals alive for its own purposes. That may be preferable to extinction, but it is not conservation, and it should not be described as such.