Biology
Seasonal behaviour
Why birds fly away in autumn and hedgehogs sleep in winter: animals time their behaviour to the seasons.
In summer it is warm and there is plenty to eat. In winter it turns cold, and food is scarce. Because of this, many animals change their behaviour over the course of the year. Some travel far, others simply sleep through the cold time. In this chapter you will look at how animals deal with the seasons.
Bird migration
Many birds fly to warmer countries in autumn, often as far as Africa. There they find enough food in winter. In spring they come back and breed here. This long journey is called bird migration. The barn swallow, for example, flies from central Europe to south of the Sahara, more than 6000 kilometres for the outward trip alone. Other birds only move a bit further south.
Hibernation and winter rest
Other animals stay but sleep through the cold time. During hibernation, for example in the hedgehog, the body slows right down: heartbeat and breathing become very slow, and the body temperature falls from around 36 to about 5 degrees Celsius. That way the hedgehog uses hardly any energy and lives all winter off the layer of fat it built up in autumn. During winter rest, such as in the squirrel, the body stays almost warm: the animal only sleeps deeply and wakes up now and then to eat from its supply.
Fast growth first, then flattening at the carrying capacity.
How do animals notice the season?
Animals do not look at a calendar. The most important trigger is day length: in autumn the days grow shorter, and by this many animals notice that winter is near. Falling temperatures and less food also play a part. These signs set the right behaviour going, long before the deepest winter arrives.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
What is the most important trigger by which animals notice winter approaching?
Which animal hibernates, with its whole body slowing right down?
The chapter distinguishes two ways of getting through winter: hibernation and winter rest. How many is that?
Match each term to the description that fits.
A bird travels south in autumn and back again in spring. How many journeys does it make in one year?
Put the stages of bird migration over the year in the right order.
- 1The birds fly to warmer countries in the south.
- 2In autumn the days grow shorter.
- 3In spring they return to breed.
- 4In winter they find enough food there.