Habitat fragmentation caused by human economic activities, such as highway construction and deforestation for pasture, is pushing many primate species toward the tragedy of local extinction. Yet, amidst this crisis, the mantled howler monkey in Costa Rica has demonstrated remarkable resilience, far outperforming its regional counterparts, the spider monkey and the capuchin monkey. The reading passage Monkeys and Forests uncovers unique biological mysteries—from plant detoxification mechanisms and high-speed reproductive strategies to the ability to adapt to agroforestry plantations.

From an IELTS perspective, this is an exemplary text on applied ecology, challenging test-takers with paraphrased expressions that connect research locations with specific animal survival behaviors.

Reading Passage

AS AN EAST WIND blasts through a gap in the Cordillera de Tilaran, a rugged mountain range that splits northern Costa Rica in half, a female mantled howler monkey moves through the swaying trees of the forest canopy.

[Paragraph A] Ken Glander, a primatologist from Duke University, gazes into the canopy, tracking the female’s movements. Holding a dart gun, he waits with infinite patience for the right moment to shoot. With great care, Glander aims and fires. Hit in the rump, the monkey wobbles. This howler belongs to a population that has lived for decades at Hacienda La Pacifica, a working cattle ranch in Guanacaste province. Other native primates – white-faced capuchin monkeys and spider monkeys – once were common in this area, too, but vanished after the Pan-American Highway was built nearby in the 1950s. Most of the surrounding land was clear-cut for pasture.

[Paragraph B] Howlers persist at La Pacifica, Glander explains, because they are leaf-eaters. They eat fruit, when it’s available but, unlike capuchin and spider monkeys, do not depend on large areas of fruiting trees. “Howlers can survive any place you have half a dozen trees, because their eating habits are so flexible,” he says. In forests, life is an arms race between trees and the myriad creatures that feed on leaves. Plants have evolved a variety of chemical defenses, ranging from bad-tasting tannins, which bind with plant-produced nutrients, rendering them indigestible, to deadly poisons, such as alkaloids and cyanide.

[Paragraph C] All primates, including humans, have some ability to handle plant toxins. “We can detoxify a dangerous poison known as caffeine, which is deadly to a lot of animals,” Glander says. For leaf-eaters, long-term exposure to a specific plant toxin can increase their ability to defuse the poison and absorb the leaf nutrients. The leaves that grow in regenerating forests, like those at La Pacifica, are actually more howler friendly than those produced by the undisturbed, centuries-old trees that survive farther south, in the Amazon Basin. In younger forests, trees put most of their limited energy into growing wood, leaves and fruit, so they produce much lower levels of toxin than do well-established, old-growth trees.

[Paragraph D] The value of maturing forests to primates is a subject of study at Santa Rosa National Park, about 35 miles northwest of Hacienda La Pacifica. The park hosts populations not only of mantled howlers but also of white-faced capuchins and spider monkeys. Yet the forests there are young, most of them less than 50 years old. Capuchins were the first to begin using the reborn forests, when the trees were as young as 14 years. Howlers, larger and heavier than capuchins, need somewhat older trees, with limbs that can support their greater body weight. A working ranch at Hacienda La Pacifica also explains their population boom in Santa Rosa. “Howlers are more resilient than capuchins and spider monkeys for several reasons,” Fedigan explains. “They can live within a small home range, as long as the trees have the right food for them. Spider monkeys, on the other hand, occupy a huge home range, so they can’t make it in fragmented habitat.”

[Paragraph E] Howlers also reproduce faster than do other monkey species in the area. Capuchins don’t bear their first young until about 7 years old, and spider monkeys do so even later, but howlers give birth for the first time at about 3.5 years of age. Also, while a female spider monkey will have a baby about once every four years, well-fed howlers can produce an infant every two years.

[Paragraph F] The leaves howlers eat hold plenty of water, so the monkeys can survive away from open streams and water holes. This ability gives them a real advantage over capuchin and spider monkeys, which have suffered during the long, ongoing drought in Guanacaste.

[Paragraph G] Growing human population pressures in Central and South America have led to persistent destruction of forests. During the 1990s, about 1.1 million acres of Central American forests were felled yearly. Alejandro Estrada, an ecologist at Estacion de Biologia Los Tuxtlas en Veracruz, Mexico, has been exploring how monkeys survive in a landscape increasingly shaped by humans. He and his colleagues recently studied the ecology of a group of mantled howler monkeys that thrive in a habitat completely altered by humans: a cacao plantation in Tabasco, Mexico. Like many varieties of coffee, cacao plants need shade to grow, so 40 years ago the landowners planted fig, monkey pod and other tall trees to form a protective canopy over their crop. The howlers moved in about 25 years ago after nearby forests were cut. This strange habitat, a hodgepodge of cultivated native and exotic plants, seems to support about as many monkeys as would a same-sized patch of wild forest. The howlers eat the leaves and fruit of the shade trees, leaving the valuable cacao pods alone, so the farmers tolerate them.

[Paragraph H] Estrada believes the monkeys bring underappreciated benefits to such farms, dispersing the seeds of fig and other shade trees and fertilizing the soil with feces. He points out that howler monkeys live in shade coffee and cacao plantations in Nicaragua and Costa Rica as well as in Mexico. Spider monkeys also forage in such plantations, though they need nearby areas of forest to survive in the long term. He hopes that farmers will begin to see the advantages of associating with wild monkeys, which includes potential ecotourism projects. “Conservation is usually viewed as a conflict between agricultural practices and the need to preserve nature,” Estrada says. “We’re moving away from that vision and beginning to consider ways in which agricultural activities may become a tool for the conservation of primates in human-modified landscapes.”

Questions

Questions 27 – 32 Reading passage 3 has 8 paragraphs, A-H. Which paragraph contains the following information? Write the correct letter, A-H, in boxes 27-32 on your answer sheet.

27. A reference of rate of reduction in forest habitats.

28. An area where only one species of monkey survived while other two species vanished.

29. A reason for howler monkeys to choose new leaves as food over old ones.

30. Mention of howler monkey’s diet and eating habits.

31. A reference of asking farmers’ to change attitude towards wildlife.

32. The advantage of howler monkey’s flexibility in living in a segmented habitat.

Questions 33 – 35 Look at the list of places and the following descriptions below. Match each description with the correct place, A-E. Write your answers, A-E, in boxes 33 – 35 on your answer sheet.

List of Places:

A. Hacienda La Pacifica

B. Santa Rosa National Park

C. A cacao plantation in Tabasco, Mexico

D. Estacion de Biología Los Tuxtlas in Veracruz, Mexico

E. Amazon Basin

33. A place where howler monkeys benefit to the local region’s agriculture.

34. A place where it is the original home for all three native monkeys.

35. A place where capuchin monkeys come for a better habitat.

Questions 36 – 40 Complete the sentences below. Choose NO MORE THAN TWO WORDS from the passage for each answer. Write your answers in boxes 36 – 40 on your answer sheet.

The reasons why howler monkeys survive better in local region than the other two species:

Howlers live better in La Pacifica since they can feed themselves with leaves when 36. _______________ is not easily found.
Howlers have better ability to alleviate the 37. _______________ which old and young trees used to protect themselves.
When compared to that of spider monkeys and capuchin monkeys, the 38. _______________ rate of howlers is relatively faster (round for just every 2 years).
The monkeys can survive away from open streams and water holes as the leaves that howlers eat hold high content of 39. _______________, which helps them to resist the continuous 40. _______________ in Guanacaste.

Full Translation of the Reading Passage

As an east wind blasts through a gap in the Cordillera de Tilaran, a rugged mountain range that splits northern Costa Rica in half, a female mantled howler monkey moves through the swaying trees of the forest canopy.

[Paragraph A] Ken Glander, a primatologist from Duke University, gazes into the canopy, tracking the female’s movements. Holding a dart gun, he waits with infinite patience for the right moment to shoot. With great care, Glander aims and fires. Hit in the rump, the monkey wobbles. This howler belongs to a population that has lived for decades at Hacienda La Pacifica, a working cattle ranch in Guanacaste province. Other native primates—white-faced capuchin monkeys and spider monkeys—were once common in this area, too, but vanished after the Pan-American Highway was built nearby in the 1950s. Most of the surrounding land was clear-cut for pasture.

[Paragraph B] Glander explains that howlers persist at La Pacifica because they are leaf-eaters. They eat fruit when it is available, but unlike capuchin and spider monkeys, they do not depend on large areas of fruiting trees. “Howlers can survive anywhere you have half a dozen trees, because their eating habits are so flexible,” he says. In forests, life is a chemical arms race between trees and the myriad creatures that feed on leaves. Plants have evolved a variety of chemical defenses, ranging from bad-tasting tannins, which bind with plant-produced nutrients and render them indigestible, to deadly poisons such as alkaloids and cyanide.

[Paragraph C] All primates, including humans, have some ability to handle plant toxins. “We can detoxify a dangerous poison known as caffeine, which is deadly to a lot of animals,” Glander says. For leaf-eaters, long-term exposure to a specific plant toxin can increase their ability to defuse the poison and absorb leaf nutrients. The leaves that grow in regenerating forests, like those at La Pacifica, are actually more howler-friendly than those produced by the undisturbed, centuries-old trees that survive farther south in the Amazon Basin. In younger forests, trees put most of their limited energy into growing wood, leaves, and fruit, so they produce much lower levels of toxin than do well-established, old-growth trees.

[Paragraph D] The value of maturing forests to primates is a subject of study at Santa Rosa National Park, about 35 miles northwest of Hacienda La Pacifica. The park hosts populations not only of mantled howlers but also of white-faced capuchins and spider monkeys. Yet the forests there are young, most of them less than 50 years old. Capuchins were the first to begin using the reborn forests, when the trees were as young as 14 years. Howlers, larger and heavier than capuchins, need somewhat older trees with limbs that can support their greater body weight. The working ranch at Hacienda La Pacifica also explains their population boom in Santa Rosa. “Howlers are more resilient than capuchins and spider monkeys for several reasons,” Fedigan explains. “They can live within a small home range, as long as the trees have the right food for them. Spider monkeys, on the other hand, occupy a huge home range, so they can’t make it in fragmented habitat.”

[Paragraph E] Howlers also reproduce faster than other monkey species in the area. Capuchins don’t bear their first young until about 7 years old, and spider monkeys do so even later, but howlers give birth for the first time at about 3.5 years of age. Also, while a female spider monkey will have a baby about once every four years, well-fed howlers can produce an infant every two years.

[Paragraph G] Growing human population pressures in Central and South America have led to persistent destruction of forests. During the 1990s, about 1.1 million acres of Central American forests were felled yearly. Alejandro Estrada, an ecologist at Estacion de Biologia Los Tuxtlas in Veracruz, Mexico, has been exploring how monkeys survive in a landscape increasingly shaped by humans. He and his colleagues recently studied the ecology of a group of mantled howler monkeys that thrive in a habitat completely altered by humans: a cacao plantation in Tabasco, Mexico. Like many varieties of coffee, cacao plants need shade to grow, so 40 years ago the landowners planted fig, monkey pod, and other tall trees to form a protective canopy over their crop. The howlers moved in about 25 years ago after nearby forests were cut. This strange habitat, a hodgepodge of cultivated native and exotic plants, seems to support about as many monkeys as would a same-sized patch of wild forest. The howlers eat the leaves and fruit of the shade trees, leaving the valuable cacao pods alone, so the farmers tolerate them.

Academic Vocabulary Summary

Primatologist (n): A scientist who studies primates.
Canopy (n): The upper layer or habitat zone of a forest.
Persist (v): To continue to exist or endure.
Myriad (adj/n): A countless or extremely great number.
Detoxify (v): To remove toxic substances.
Resilient (adj): Able to withstand or recover quickly from difficult conditions.
Fragmented habitat (phrase): An environment broken into smaller, isolated patches.
Felled (v): Cut down (trees).
Hodgepodge (n): A confused mixture or jumble.
Ecotourism (n): Tourism directed toward exotic, often threatened, natural environments.

Detailed Answer Key

Questions 27 – 32: Paragraph Matching

27. A reference of rate of reduction in forest habitats.

Answer: G

Explanation: The beginning of paragraph G provides specific data on the rate of forest loss: “During the 1990s, about 1.1 million acres of Central American forests were felled yearly.” The phrase “rate of reduction” corresponds to the number of acres cleared annually.

28. An area where only one species of monkey survived while other two species vanished.

Answer: A

Explanation: Paragraph A discusses the Hacienda La Pacifica ranch. Howlers persisted here, while: “Other native primates – white-faced capuchin monkeys and spider monkeys – once were common in this area, too, but vanished after the Pan-American Highway was built…”

29. A reason for howler monkeys to choose new leaves as food over old ones.

Answer: C

Explanation: Paragraph C explains that leaves in regenerating (young) forests are easier to eat than those in old-growth Amazon forests because young trees prioritize wood growth over toxin production: “In younger forests, trees… produce much lower levels of toxin than do well-established, old-growth trees.”

30. Mention of howler monkey’s diet and eating habits.

Answer: B

Explanation: The first sentence of paragraph B confirms the howler’s dietary nature: “Howlers persist… because they are leaf-eaters. They eat fruit, when it’s available but… do not depend on large areas of fruiting trees.”

31. A reference of asking farmers’ to change attitude towards wildlife.

Answer: H

Explanation: Paragraph H expresses the desire to change farmers’ perspectives: “He hopes that farmers will begin to see the advantages of associating with wild monkeys… become a tool for the conservation…”

32. The advantage of howler monkey’s flexibility in living in a segmented habitat.

Answer: D

Explanation: The end of paragraph D compares howlers to spider monkeys in fragmented environments: “They can live within a small home range… Spider monkeys, on the other hand… can’t make it in fragmented habitat.”

Questions 33 – 35: Matching Features (Places)

33. A place where howler monkeys benefit to the local region’s agriculture.