Grade by Grade
B. Life Systems · Growth and Changes in Animals

Bird and Mammal Life Cycles

B2.3 B2.4 A1.5About 40 minutes
Learning goals
  • I can describe the life cycle of a bird: egg, hatchling, nestling, fledgling, adult.
  • I can describe the life cycle of a mammal, including people.
  • I can tell how parents care for their young and how the young change as they grow.

Words to know

incubate
To keep eggs warm, usually by sitting on them, until they hatch.
hatchling
A baby bird that has just come out of its egg.
nestling
A young bird that is still living in the nest and being fed by its parents.
fledgling
A young bird that has just left the nest and is learning to fly.
gosling
A baby goose.
cub
A baby bear (also a baby fox or wolf).
nurse
When a mammal baby drinks milk from its mother.

A nest by the window

In May, a robin built a nest of grass and mud on the Singhs' porch light. Soon there were 4 bright blue eggs in it! The family watched every day from the window. What do you think happened next?

A robin's nest made of grass on a porch, holding four bright blue eggs.
A robin's nest with 4 blue eggs, just like the Singhs'. This is the egg stage of the robin's life cycle. AI-generated image

A bird's life cycle

All birds hatch from eggs with hard shells. Here is a robin's life cycle:

  1. Egg: The mother robin lays 3 to 5 blue eggs, one each day. She sits on them to keep them warm. This is called incubating. After about 2 weeks, the eggs hatch.
  2. Hatchling: The babies have almost no feathers, and their eyes are closed. They cannot fly or find food.
  3. Nestling: Both parents bring worms and insects to feed them. The babies grow feathers fast.
  4. Fledgling: About 2 weeks after hatching, the young robins leave the nest. They hop on the ground and flutter, learning to fly. Their parents still feed them for a while. Their chests are spotted.
  5. Adult: By next spring, the young robin is an adult with a red-orange chest. It can build a nest and lay eggs.
startweek 1week 2week 3week 4eggs are incubated (about 2 weeks)babies fed in the nest (about 2 weeks)eggs laideggs hatchfledglings leave nest2 weeks + 2 weeks = about 4 weeks from egg to leaving the nest
A robin timeline. Eggs hatch after about 2 weeks, and the young leave the nest about 2 weeks later.
egghatchlingnestlingfledglingadultrobinthe adult has young, and the cycle starts again
The life cycle of a robin.

Not all bird babies are the same

A Canada goose makes a nest on the ground near water. Its babies, called goslings, hatch covered in fluffy yellow down (soft feathers) with their eyes open. Within a day, they can walk, swim and find their own food! Their parents still guard them closely. They learn to fly when they are about 2 months old.

So robin babies need lots of care in the nest, while goslings can do more right away.

A mammal's life cycle

Most mammals are born live (not from an eggshell). The babies drink milk from their mother (they nurse). They grow up and become adults that can have babies.

Black bear:

  1. Birth: In January or February, in a winter den, the mother bear gives birth to tiny cubs. Each cub is about as heavy as a can of soup! Their eyes are closed and they have very little fur. They nurse and grow in the den.
  2. Cub: In spring, the cubs leave the den with their mother. She teaches them to find food: berries, plants, insects and more. They climb trees to stay safe.
  3. Young bear: The cubs stay with their mother for about a year and a half. Then they go off on their own.
  4. Adult: After a few more years, they are grown up and can have cubs of their own.
Robin 🐦Canada goose 🪿Black bear 🐻
How it startseggeggborn live
Babies are calledhatchlings, nestlings, fledglingsgoslingscubs
Babies at firstno feathers, eyes closedfluffy down, eyes openlittle fur, eyes closed
Food at firstworms and insects from parentsfinds own grass and plantsmother's milk
Parent careboth parents feed themboth parents guard themmother feeds, teaches and protects them
Comparing a bird that needs lots of care, a bird that is ready early, and a mammal

Your life cycle!

People are mammals too. Your life cycle is: baby → child → teenager → adult. As a baby, you drank milk and needed someone to do everything for you. Now you can walk, talk, read and help others. Someday you will be an adult. Your body covering (skin and hair) stays the same, but your size and what you can do keep changing.

Just for fun

Which side of a robin has the most feathers?

The outside!

Worked example

Let's put a robin's life in order

Order these: fledgling, egg, adult, hatchling, nestling.

  1. Start with the egg in the nest.
  2. The bird that has just hatched is a hatchling.
  3. While it grows feathers in the nest, it is a nestling.
  4. When it leaves the nest and learns to fly, it is a fledgling.
  5. When it is grown and can raise its own babies, it is an adult.

egg → hatchling → nestling → fledgling → adult

Worked example

Let's compare a bear cub and an adult bear

How does a black bear's appearance and behaviour change as it grows?

  1. Size: a newborn cub is tiny, about as heavy as a can of soup. An adult can be heavier than a grown-up person.
  2. Body covering: newborn cubs have very little fur. Adults have thick black fur. It is still fur, so the kind of covering stays the same.
  3. Food: cubs drink milk. Adults find berries, plants, insects and other food.
  4. Behaviour: cubs follow their mother and learn from her. Adults live on their own.

The bear gets much bigger and more independent, but it does not change its body shape like a frog. A cub looks like a small bear.

Hands-on activity

My own life cycle timeline

You need: 4 photos of you at different ages (or drawings), a long strip of paper, glue or tape, and a grown-up to help.

  1. Line up the photos from youngest to oldest on the paper strip.
  2. Under each one, write or say: How old was I? What could I do? What did I eat?
  3. At the end, draw yourself as an adult. What will you be able to do?
  4. Ask a grown-up: "What was I like as a baby?" Add one fact they tell you.
  5. Share your timeline with your family or a friend, like a scientist presenting.

What to look for: photos in the right order, and at least one change in appearance (size, hair, teeth) and one change in behaviour (walking, talking, eating).

Your turn

1

Name the 5 stages of a robin's life cycle in order.

2

What does incubate mean?

3

What colour are robin eggs?

4

How is a gosling different from a robin hatchling?

5

What do black bear cubs eat when they are first born?

6

How long do black bear cubs stay with their mother?

7

What are the stages of a person's life cycle?

More practice: warm-up

1

Do birds hatch from eggs or are they born live?

2

What is a baby goose called?

3

What is a baby bear called?

4

Are you a mammal?

5

What is a young bird that has just left the nest called?

More practice: on your own

1

A robin's eggs take about 2 weeks to hatch. The babies leave the nest about 2 weeks later. About how many weeks from egg to leaving the nest?

2

Where is a black bear cub born, and in what season?

3

You find a spotty-chested young robin hopping on the lawn. Should you take it inside? Why or why not?

4

Give one way a bird life cycle and a mammal life cycle are different.

5

Does a bear go through metamorphosis like a frog? Explain.

Challenge

1

Why do you think goslings can leave the nest so soon, but robin babies stay in the nest about 2 weeks?

2

Compare a robin's life cycle and a black bear's life cycle. Give one way they are the same and one way they are different.

3

Why is it important for a mother bear to teach her cubs where to find food?

Check your understanding

Quiz

1.

What is the right order for a bird?

2.

What does it mean to incubate eggs?

3.

What do mammal babies drink?

4.

Which baby can swim and find its own food within a day of hatching?

5.

Where are black bear cubs born?

6.

Which animal does not go through metamorphosis?

For parents and teachers

Big idea: Birds hatch from eggs and go through hatchling, nestling and fledgling stages before becoming adults; most mammals are born live and nurse (B2.3). Young birds and mammals generally look like smaller versions of the adult, and behaviour changes a lot as they become independent (B2.4). Some baby birds (goslings, ducklings) are ready to move and feed very early; others (robins, chickadees) need a lot of care.

Communicating (A1.5): The life-cycle timeline lets your child organize information in order and present it.

Accuracy notes: A newborn black bear cub weighs roughly 300 grams. Robin incubation and nestling times are each about two weeks. Fledgling robins on the ground in early summer are normal; parents are usually close by.

Common difficulties:

  • Mixing up nestling and fledgling. Nestling = in the nest. Fledgling = has left and is learning to fly.
  • Thinking all babies need the same care. Compare goslings and robins.

How to help: Watch a nest from a distance (never touch it). Look through family photos together and talk about how your child has changed.