STANDARDS

CCSS: 7.RP.A.3, MP2, MP3, MP8

TEKS: 7.4D, 6.4G

Gorilla Census

Scientists hike through African forests to track the population of endangered apes

Thomas Marent/Minden Pictures

Fiona Maisels can identify gorilla dung in an instant. It’s bulky and segmented and it looks like it came from a pony. When she spots droppings on the forest floor in Central Africa, “it’s really obvious” who made it, she says.

Maisels is an ecologist who monitors animal populations for the Wildlife Conservation Society. She recently helped coordinate the most thorough survey ever of western lowland gorillas in the wild. Over the course of 11 years, more than 50 scientists used droppings and other clues to count gorillas in the forest. They used that data to estimate the total number of the apes alive.

Fiona Maisels knows exactly what gorilla dung looks like. It’s bulky and divided into rounded segments. It looks like it came from a pony. When Maisels spots droppings on the forest floor in Central Africa, “it’s really obvious” who made them, she says.

Maisels is an ecologist. She monitors animal populations for the Wildlife Conservation Society. She recently helped coordinate a survey of western lowland gorillas in the wild. It was the most thorough count scientists had ever made. The survey took 11 years and more than 50 scientists. They used droppings and other clues to count gorillas in the forest. Then they used that data to estimate the total number of the apes alive.

Jim McMahon/Mapman

Almost all the world’s gorillas live near the equator in Central Africa (see map). To protect the endangered animals, scientists need to know which regions they inhabit and how many of them there are. To find out, teams of researchers like Maisels spent months at a time trekking through national parks and other wilderness areas. They camped in the forest, arose before dawn, and hurried to eat breakfast before any hungry insects woke up. Then they walked a straight line through the forest to gather evidence of animals around them. They repeated this thousands of times over more than a decade to survey large swaths of the wilderness.

Almost all the world’s gorillas live near the equator in Central Africa (see map). The animals are endangered. To protect them, scientists need to know which regions they inhabit and how many of them there are. To find out, teams of researchers like Maisels spent months at a time on expeditions. They trekked through national parks and other wilderness areas. They camped in the forest and got up before dawn. They had to eat breakfast quickly, before any hungry insects woke up. Then they walked a straight line through the forest to gather evidence of animals around them. They repeated this thousands of times over more than a decade. Over time, they surveyed large portions of the wilderness.

Eric Baccega/NaturePL

Finding gorillas isn’t easy. If the big apes hear people coming, they usually run away. Instead, the scientists looked for the nests that gorillas build to sleep in. Apes make these beds of sticks and leaves each evening and abandon them the next day. When the team spotted an ape nest, they checked under it for droppings. The shape of the dung told them whether the nest was used by a gorilla or a chimp.

After dozens of expeditions, the researchers had enough data to estimate the total number of gorillas in western Africa. They calculated that there were more than 360,000 of the apes in 2013—at least 100,000 more than previously known.

Unfortunately, over the course of the study, the population shrank by an average of 2.7 percent each year. Poaching, disease, and habitat loss are making it harder for gorillas to survive. 

A healthy gorilla population can help the whole forest, says Maisels. As the apes eat fruits, they spread seeds in their dung, allowing new trees to grow. Maisels hopes that the data scientists have gathered will bring new protections for the animals. “We should go to great lengths to reverse the damage we’ve done,” she says.

Finding gorillas isn’t easy. If the big apes hear people coming, they usually run away. Instead, the scientists looked for the nests that gorillas build to sleep in. Apes make these beds of sticks and leaves each evening. They abandon the nests the next day. When the team spotted an ape nest, they checked under it for droppings. They studied the shape of the dung. That told them whether the nest was used by a gorilla or a chimp.

After dozens of expeditions, the researchers had the data they needed. It was enough to estimate the total number of gorillas in western Africa. They calculated that there were more than 360,000 of the apes in 2013. That’s at least 100,000 more than previously known.

Unfortunately, the population dropped over the course of the study. It shrank by an average of 2.7 percent each year. Poaching, disease, and habitat loss are making it harder for gorillas to survive.

A healthy gorilla population helps the whole forest, says Maisels. As the apes eat fruits, they spread seeds in their dung. That allows new trees to grow. Maisels hopes that the data scientists have gathered will help gorillas. It could inspire new protections for the animals. “We should go to great lengths to reverse the damage we’ve done,” Maisels says.

Use the information in the chart to answer the following questions. Round all answers to the nearest whole percent. Record your work and answers on our answer sheet.

Use the information in the chart to answer the following questions. Round all answers to the nearest whole percent. Record your work and answers on our answer sheet.

Complete the chart below to determine the percent change in the gorilla population in each country and in total.

Complete the chart below to determine the percent change in the gorilla population in each country and in total.

Which country saw the smallest percent change in gorilla population?

Which country saw the smallest percent change in gorilla population?

How did the population change in the Central African Republic compare with that in Equatorial Guinea?

How did the population change in the Central African Republic compare with that in Equatorial Guinea?

A. Scientists determine if a species is endangered based on the percent change in its population over three generations. If the gorilla population continues to change at the current rate, there will be about 61,083 animals after three generations. What percent change from the 2013 total population would that be

A. Scientists determine if a species is endangered based on the percent change in its population over three generations. If the gorilla population continues to change at the current rate, there will be about 61,083 animals after three generations. What percent change from the 2013 total population would that be

B. A species is classified as endangered if its population will decrease by 50% or more over three generations. It is critically endangered if it will decrease by more than 80% over three generations. Based on your answer to 4A, how should gorillas be classified? Explain your reasoning.

B. A species is classified as endangered if its population will decrease by 50% or more over three generations. It is critically endangered if it will decrease by more than 80% over three generations. Based on your answer to 4A, how should gorillas be classified? Explain your reasoning.

Back to top
videos (1)
Skills Sheets (4)
Skills Sheets (4)
Skills Sheets (4)
Skills Sheets (4)
Lesson Plan (2)
Lesson Plan (2)