Grade by Grade
B. Life Systems · Habitats and Communities

When a Species Disappears: Depletion and Extinction

B1.2 B2.4 A1.3 A3.1 A1.5About 45 minutes
Learning goals
  • I can explain the words depleted, endangered, extirpated and extinct.
  • I can analyse how losing a species affects its habitat and community.
  • I can describe actions that help prevent depletion and extinction.
  • I can use the engineering design process to design a solution that protects an animal.

Words to know

depleted
When a population has become much smaller than it used to be.
species at risk
A species that could disappear from an area or from Earth if nothing changes.
endangered
A species at risk that is close to disappearing.
extirpated
When a species is gone from one area (like Ontario) but still lives somewhere else.
extinct
When a species is gone everywhere on Earth, forever.
engineering design process
Steps engineers use to solve a problem: define the problem, brainstorm, plan, build, test, and improve.

The missing birds

Long ago, passenger pigeons flew over Ontario in flocks so huge that people said they darkened the sky for hours. There were billions of them.

People hunted them in enormous numbers, and the forests where they nested were cut down. Their numbers crashed. The very last passenger pigeon, named Martha, died in a zoo in Cincinnati, in the United States, in 1914.

The passenger pigeon is extinct. It is gone forever. Its story teaches us why we need to act before a species disappears.

Words scientists use

  • Depleted: the population is much smaller than it used to be.
  • Species at risk: a species that could disappear if nothing changes. Endangered species are the closest to disappearing.
  • Extirpated: gone from one area, such as Ontario, but still alive somewhere else.
  • Extinct: gone from everywhere on Earth, forever.
healthypopulationdepletedendangeredextinctA species can slide toward extinction. Action can stop the slide.
From a healthy population to extinction. The earlier people act, the easier it is to help.

Why losing one species matters

Remember the food web: every species is connected. When one species is depleted or disappears:

  • Animals that ate it lose food. They may go hungry or eat more of something else.
  • Organisms it ate may increase too much, because nothing keeps them in check.
  • Plants it helped (by pollinating or spreading seeds) may make fewer seeds.
  • The habitat itself may change. When beavers are removed from an area, their dams break down, ponds drain, and the frogs, fish and ducks that used the pond lose their habitat.
Worked example

Let's analyse a loss

Wild bees and other pollinators are declining in many places. Predict how fewer pollinators could affect a meadow community.

  1. What do pollinators do? They carry pollen from flower to flower so plants can make seeds and fruits.
  2. Effect on plants: fewer pollinators → fewer wildflowers and berry plants make seeds → fewer new plants next year.
  3. Effect on animals that eat seeds and berries: birds, mice and bears that eat seeds and berries have less food.
  4. Effect on predators: animals that eat those plant-eaters (like foxes and hawks) may also have less food.
  5. Effect on people: many of our fruits and vegetables, like apples, blueberries and squash, need pollinators too.

Losing pollinators would ripple through the whole food web, including to people.

Good news: people can turn things around

Ontario has real success stories:

  • Peregrine falcons almost disappeared from Ontario because a pesticide called DDT made their eggshells so thin they broke. After DDT was banned and people raised and released young falcons, peregrines nest in Ontario again, even on ledges of tall buildings in cities.
  • Trumpeter swans had disappeared from Ontario because of hunting. Starting in the 1980s, people raised and released swans, and now trumpeter swans nest in Ontario again.
  • Atlantic salmon disappeared from Lake Ontario more than 100 years ago, because of overfishing, dams and damaged streams. Groups are now working to bring them back by raising young salmon and restoring streams.
Two white trumpeter swans with black bills swimming in a marsh.
Trumpeter swans once disappeared from Ontario. Because people raised and released young swans, they nest here again. AI-generated image
ProblemAction that helps
habitat lossprotect parks, wetlands and forests; restore habitats
pollution and pesticidesuse fewer chemicals; ban the most harmful ones; clean up water
overhunting and overfishingrules on how many can be caught, and when
invasive speciesdon't move firewood; clean boats; remove invasive plants
roadswildlife crossings, fences and signs
birds hitting windowswindow decals or screens; turning off building lights at night during migration
very small populationsraise young animals and release them into protected habitat
Actions people take to prevent depletion and extinction.

What can a Grade 4 student do?

Plant native flowers like milkweed, keep pet cats indoors (cats hunt many birds), put stickers or decals on big windows, pick up litter, never release pet fish or plants into the wild, and report what you see to a nature-sighting app with a grown-up. Small actions by many people add up!

Worked example

Let's use the engineering design process

Problem: Turtles get hit by cars when they cross a road between a pond and their nesting area. Design a solution.

  1. 1. Define the problem: turtles need to get safely from one side of the road to the other.
  2. 2. Brainstorm: a tunnel under the road; fences that guide turtles to the tunnel; signs for drivers.
  3. 3. Plan: a tunnel big enough for turtles, with low fences on both sides of the road that lead to the tunnel entrance.
  4. 4. Build a model: a cardboard box "road", a paper towel tube tunnel, cardboard fences.
  5. 5. Test: push a toy turtle along the fence from different starting spots. Does it always reach the tunnel?
  6. 6. Improve: in testing, the turtle slipped around the end of the fence, so the fence was made longer and curved back at the ends.

An improved model that guides turtles to a tunnel. Real wildlife crossings like this are built in Ontario by engineers, biologists and construction workers.

pondsandy nesting arearoadtunnel under the roadfence
A top view of the turtle crossing design (not to scale). Fences along the road guide turtles to a tunnel, and the fence ends curve back so turtles can't slip around them.
Just for fun

Some good news with a twist: peregrine falcons, which almost disappeared from Ontario, now nest on ledges of tall city buildings. When they dive for prey, they are among the fastest animals on Earth, faster than a car on the highway!

Hands-on activity

Design a wildlife crossing model

You need: a shoebox or cardboard (the road), paper towel or toilet paper tubes, scrap cardboard, tape, a small toy animal or a bottle cap "turtle", a ruler.

  1. Define the problem: an animal must cross a road safely.
  2. Brainstorm at least 3 ideas and sketch them.
  3. Plan your best idea. List your materials and label your sketch with measurements in centimetres.
  4. Build your model.
  5. Test it 5 times, starting the toy animal from different places. Record how many times it reached the other side without touching the road.
  6. Improve your design and test again. Did your score go up?
  7. Communicate: explain your design to your family, using the words habitat, species at risk and engineering design process.

Grown-up note (safety): An adult does any cutting of thick cardboard with scissors or a craft knife. Keep bottle caps and other small parts away from young children (choking hazard).

Your turn

1

What does extinct mean?

2

What is the difference between extirpated and extinct?

3

Why did the passenger pigeon become extinct?

4

If a species of mouse disappeared from a forest, which animals might be affected first?

5

Name two actions that help prevent extinction.

6

What made peregrine falcon eggshells break?

7

What are the steps of the engineering design process?

More practice: warm-up

1

Is the passenger pigeon extinct or endangered?

2

What does depleted mean?

3

Name a bird that has come back in Ontario thanks to people's help.

4

What flower can you plant to help monarch butterflies?

5

Why should pet cats stay indoors?

More practice: on your own

1

Beavers are trapped out of a valley. Explain what could happen to the pond and the animals that use it.

2

Why is it easier to help a species that is depleted than one that is nearly extinct?

3

Martha the passenger pigeon died in 1914. How many years ago was that from 2026?

4

Why do some cities turn off building lights at night during bird migration?

5

In the turtle crossing example, what problem did testing show, and how was it fixed?

Challenge

1

Wolves are top predators. Explain how removing all the wolves from an area could harm young trees.

2

Atlantic salmon disappeared from Lake Ontario. Were they extinct or extirpated? Explain.

3

Choose one species at risk you know (such as the monarch butterfly). Describe one cause of its decline and design one action your community could take.

Check your understanding

Quiz

1.

A species that is gone from everywhere on Earth is...

2.

A species gone from Ontario but still living in other places is...

3.

The last passenger pigeon died in...

4.

If pollinators disappeared from a meadow, what would most likely happen?

5.

Which action helps prevent extinction?

6.

Which step comes right after build in the engineering design process?

7.

Peregrine falcons came back in Ontario after...

For parents and teachers

This lesson analyses what happens when a species is depleted or disappears, and what people can do to prevent it. It uses the engineering design process to design a wildlife crossing model.

Common difficulties:

  • Mixing up extirpated (gone from one area) and extinct (gone everywhere).
  • Feeling worried or sad. Balance hard news with the success stories (peregrine falcons, trumpeter swans) and with real actions children can take.

Safety: An adult handles scissors or craft knives; keep small parts away from young children.

At home: Plant a native flower, put decals on a big window, or check a local conservation authority's website for family volunteer days.