---
title: "Animals Through the Seasons"
book: "Primary & Middle School Biology"
subject: biology
language: en
chapter: 20
exercises: 10
source: https://one-course.com/books/biology/1/en/chapter/20-animals-through-the-seasons
---

# Chapter 20 — Animals Through the Seasons

In October the swallows line up on the wires and, one morning, they are gone. The hedgehog under the hedge rolls itself into its [leaf](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) nest and will not be seen before spring. The fox, meanwhile, is out in every snow. Winter is a hard season — cold, and above all short of food — and [animals](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) have three great ways through it.

## 20.1 Winter, the season of scarcity

**Proposition 20.1 (Winter’s double problem).**

Winter brings [animals](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) two problems at once:

1. *cold* , which drains body warmth faster — and keeping warm costs [energy](https://one-course.com/books/biology/1/en/chapter/18-a-balanced-diet#prop-g3-balanced-diet-jobs) ( [Proposition 18.1](https://one-course.com/books/biology/1/en/chapter/18-a-balanced-diet#prop-g3-balanced-diet-jobs) );
2. *scarce food* : [plants](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-plant) stop growing, [insects](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups) disappear, the first links of the [food chains](https://one-course.com/books/biology/1/en/chapter/19-food-chains#def-g3-food-chains-chain) of [Chapter 19](https://one-course.com/books/biology/1/en/chapter/19-food-chains#ch-g3-food-chains) thin out — so the scarcity travels up to everyone.

More warmth needed, less food to pay for it: that is the winter problem every [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) must solve.

**Proof.** *Admitted at this level.* ∎

**Example 20.2 (Where did the insect-eaters’ food go?).**

The swallow feeds on flying [insects](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups), caught on the wing. In November there are simply none: too cold. No change of menu can fix that for a bird built for aerial hunting — the swallow’s food supply vanishes completely.

![October on the wires: the swallows gathering for departure, days before the insects run out.](https://one-course.com/images/onecourse/chapters/biology-1/g3-animals-through-seasons/img-b36a6c43da8b.jpg)

*October on the wires: the swallows gathering for departure, days before the [insects](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups) run out.*

## 20.2 Three answers to winter

**Definition 20.3 (Migration).**

To *migrate* is to travel, each year, from one region to another as the seasons change — leaving before winter for warmer lands where food remains, and returning in spring. The swallow, the stork and the crane are *migrators*; some travel thousands of kilometres, and find their way back to the very same nest.

**Definition 20.4 (Hibernation).**

To *hibernate* is to spend the winter in a deep, cold [sleep](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs), hidden in a shelter: the body cools, heart and breathing slow to almost nothing, and the [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) lives slowly off fat stored up in autumn. The hedgehog, the dormouse, the marmot and the bat hibernate.

**Definition 20.5 (Staying active).**

The rest *stay active* and change their equipment or their habits: a thicker *winter coat*, food *stores* gathered in autumn (the squirrel’s buried nuts), a switch of menu ([Example 10.8](https://one-course.com/books/biology/1/en/chapter/10-what-animals-eat#ex-g2-what-animals-eat-winter)’s blackbird), or simply harder searching — the fox, the deer, the robin.

![Three ways through the same winter. Each solves the double problem — warmth and food — differently.](https://one-course.com/images/onecourse/chapters/biology-1/g3-animals-through-seasons/fig-cb2454c7f379.svg)

*Three ways through the same winter. Each solves the double problem — warmth and food — differently.*

**Example 20.6 (Three neighbors, three strategies).**

One hedgerow in January: the swallows that nested above it are in Africa, catching [insects](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups) under a warm sun; the hedgehog below it [sleeps](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs) cold and slow in its [leaf](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts) nest, burning August’s fat; the robin on top of it, in its puffed-up winter plumage, patrols for the last berries. Come April, all three will be busy in the same hedge again.

**Remark 20.7 (Sleep is not laziness, travel is not tourism).**

Each strategy has its price. The migrator risks an exhausting journey; the hibernator must gather every gram of its winter fat in autumn — a hedgehog too thin in November will not wake in spring; the active [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) gambles on finding food through the hungriest months. Winter is paid for in advance, or en route, or day by day.

**Method 20.8 (Guessing an animal’s winter strategy).**

1. Ask what it eats, and whether that food exists here in winter;
2. food completely gone (flying [insects](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups) , nectar): expect [migration](#def-g3-animals-through-seasons-migration) or hibernation;
3. food findable ( [seeds](https://one-course.com/books/biology/1/en/chapter/16-flowers-fruits-and-seeds#prop-g3-flowers-fruits-seeds-transform) , berries, prey): expect an active winter, perhaps with a thicker coat or stores;
4. check in autumn: fattening up and digging a nest points to hibernation; gathering in flocks points to departure.

**Example 20.9 (Spring undoes it all).**

In March and April the order reverses: [insects](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups) return, the [migrators](#def-g3-animals-through-seasons-migration) reappear at their old nests, the hibernators wake thin and ravenous, [winter coats](#def-g3-animals-through-seasons-active) are shed. The seasons turn, and the [animals](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal)’ calendar turns with them — next autumn, the swallows will line up on the wires again.

## 20.3 Exercises

**Exercise 20.1 ★.**

What double problem does winter set every [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal)?

**Solution of Exercise 20.1.**

Cold, which makes keeping warm cost more [energy](https://one-course.com/books/biology/1/en/chapter/18-a-balanced-diet#prop-g3-balanced-diet-jobs) — at the very time when food, the source of that [energy](https://one-course.com/books/biology/1/en/chapter/18-a-balanced-diet#prop-g3-balanced-diet-jobs), becomes scarce.

**Exercise 20.2 ★.**

Name the three winter strategies, with two [animals](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) for each.

**Solution of Exercise 20.2.**

[Migrate](#def-g3-animals-through-seasons-migration): the swallow, the stork (or crane). [Hibernate](#def-g3-animals-through-seasons-hibernation): the hedgehog, the marmot (or dormouse, bat). [Stay active](#def-g3-animals-through-seasons-active): the fox, the squirrel (or robin, deer).

**Exercise 20.3 ★.**

What happens to a hibernating hedgehog’s body during its long [sleep](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs)? What does it live on?

**Solution of Exercise 20.3.**

Its body cools, its heart and breathing slow to almost nothing, and it [sleeps](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs) deeply in its shelter. It lives off the fat it stored up in autumn.

**Exercise 20.4 ★.**

Why exactly must the swallow leave — what is its food, and what becomes of it here in winter?

**Solution of Exercise 20.4.**

The swallow eats flying [insects](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups) caught on the wing — and in winter here there are none at all. With its food supply gone completely, it must go where [insects](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups) still fly: warmer lands.

**Exercise 20.5 ★.**

Give three ways an active [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) gets through winter, each with its [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal).

**Solution of Exercise 20.5.**

A thicker [winter coat](#def-g3-animals-through-seasons-active) (the fox, the deer); [food stores](#def-g3-animals-through-seasons-active) gathered in autumn (the squirrel’s buried nuts); a changed menu (the blackbird switching from worms to berries); and harder searching (the robin patrolling for the last berries).

**Exercise 20.6 ★.**

What is each strategy’s price, by [Remark 20.7](#rem-g3-animals-through-seasons-cost)?

**Solution of Exercise 20.6.**

The migrator risks an exhausting journey; the hibernator must gather all its winter fat in autumn or not wake in spring; the active [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) gambles on finding food through the hungriest months.

**Exercise 20.7 ★.**

In autumn, an [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) is seen eating hugely and lining a hole with dry [leaves](https://one-course.com/books/biology/1/en/chapter/3-plants-around-us#def-g1-plants-around-us-parts). Which strategy is it preparing? Which step of [Method 20.8](#met-g3-animals-through-seasons-guess) told you?

**Solution of Exercise 20.7.**

Hibernation — eating hugely builds the winter fat, the leaf-lined hole is the winter nest. Step 4: the autumn check (fattening up and digging a nest points to hibernation).

**Exercise 20.8 ★.**

Try it: keep a winter list of the [birds](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups) you actually see outside during one cold week. Are the swallows on it? Which of your [birds](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups) chose the active strategy?

**Solution of Exercise 20.8.**

Open answer. No swallows in winter — they are in Africa. The [birds](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups) actually seen (robins, tits, blackbirds, sparrows, crows) are the active-strategy ones.

**Exercise 20.9 ★★.**

Use [Method 20.8](#met-g3-animals-through-seasons-guess) on: (a) the squirrel (eats nuts and [seeds](https://one-course.com/books/biology/1/en/chapter/16-flowers-fruits-and-seeds#prop-g3-flowers-fruits-seeds-transform)); (b) the crane (eats frogs and [insects](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups) of wet meadows). What does each likely do in winter?

**Solution of Exercise 20.9.**

(a) The squirrel’s food is findable in winter — especially buried in autumn — so: active, living on its stores. (b) The crane’s frogs and [insects](https://one-course.com/books/biology/1/en/chapter/14-sorting-living-things#prop-g3-sorting-living-things-groups) vanish from frozen wet meadows — food gone, so: [migration](#def-g3-animals-through-seasons-migration) (cranes indeed fly south in great V-shaped flocks).

**Exercise 20.10 ★★.**

A mild autumn keeps a young hedgehog awake and hunting late, but it stays thin. Why is this dangerous for it, by [Remark 20.7](#rem-g3-animals-through-seasons-cost)? What do [animal](https://one-course.com/books/biology/1/en/chapter/2-animals-around-us#def-g1-animals-around-us-animal) rescuers do with too-thin autumn hedgehogs?

**Solution of Exercise 20.10.**

A hibernator pays for winter in advance, with autumn fat; a thin hedgehog has nothing to burn through its months of cold [sleep](https://one-course.com/books/biology/1/en/chapter/6-healthy-habits#prop-g1-healthy-habits-needs) and will not wake. Rescuers take in too-thin autumn hedgehogs and feed them indoors until they weigh enough to [hibernate](#def-g3-animals-through-seasons-hibernation) safely — or keep them warm and fed through the winter.