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Part XVIII: Energy and Activity : Activity in a Changing Climate Index

Activity in a Changing Climate
How 'Warm-Blooded' Animals stay Warm
How 'Warm-Blooded' Animals stay Cool
Keeping warm Requires Energy
Chapter Summary (useful for revision)
Questions relating to this chapter

Topic Chapters Index

 

A day in the life of a lizard

Wall lizard coming out of its hole © Paul Billiet

01 hours- At night when the air is cold, the body of the lizard cools down. The lizard sleeps in its hole.

08 hours - The sun rises and during the morning the air warms up. Eventually, the sleepy lizard crawls out of its hole into the sunlight. The lizard will find a piece of rock or sandy ground which is exposed to the sun and it will lie there. In this way the lizard warms its body up above the air temperature. This is called basking.

Wall lizard basking in the sun © Paul Billiet

10 hours - The lizard is quite active now, hunting for food and defending its territory.

12 hours - The temperature in full sunlight can reach 40°C or 50°C in tropical regions. This could be dangerous for the lizard; it could become too hot. The lizard retreats to its hole to find some shade.

17 hours - The Sun's heat cools down so the lizard can come out of its hole to hunt again

Wall lizard © Paul Billiet

21 hours - The sun goes down and night falls. Gradually the air becomes colder and the lizard returns to its hole to sleep.

In this way the lizard has kept its body temperature constant right through the day. Only at night does the lizard's body become too cold to remain active.

 

 

A basking dragonfly © Paul Billiet

A basking dragonfly

 

ENERGY AND ACTIVITY

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'Cold-blooded' Animals

If a reptile such as a lizard is kept in a laboratory, we can change the temperature of the air surrounding the lizard. When we do this we observe that the body temperature of the lizard changes with the temperature of the laboratory. When the air is hot the lizard's body becomes hot and when the air is cooled down the lizard's body becomes cool. This made scientists think that reptiles and other 'cold-blooded' animals always have the same body temperature as their environment.

 

A slow worm © Paul Billiet

A slow worm is really a lizard which never grows legs. It is often found basking in the sun in sandy places.

 

When the scientists started to observe these animals where they live in the wild they observed something different. They saw that animals like the lizard change their behaviour when the temperature of the air changes.

Insects are considered to be 'cold-blooded' animals. When insects are resting their bodies do have the same temperature as the air that surrounds them. Some insects, such as the bumble bee, are well protected from cold weather.

 

A bumble bee © Paul Billiet

 

Bumble bees are covered in a thick layer of furry scales. This insulates their bodies against the cold air. Bumble bees like most insects can only fly if their flight muscles are above 27°C. When they are flying the body temperature of a bumble bee is between 30°C and 40°C. When the air is cold, such as early in the morning, the bumble bee will hang from a leaf or a flower to warm up in the sunshine. To raise its body temperature even higher the bumble bee can shiver its flight muscles like we shiver when we are cold. This means that the bumble bees will be amongst the first insects to start flying each day.

Dragonflies are large insects that may be found in many different climates. Dragonflies, like bumble bees can warm up their muscles by shivering. If the air temperature is 12°C a dragonfly can warm its flight muscles up to 30°C in about 4 minutes by shivering.

Dragonflies also bask in the sunshine to warm up. Some species have dark patches on their wings to help them warm up quickly in the sun because dark bodies warm up more quickly than pale bodies.

If the sun is too hot the dragonfly tries to avoid exposing its body to the sun by raising its abdomen into the air or it will retreat to the shade of a tree.

Moths which fly at night are probably the insects which are most resistant to cold temperatures. Some species of moths can fly in the winter when the air temperature is 0°C. However, their flight muscles can only work at 30°C and it takes the moth 22 minutes to warm up by shivering. Once they are flying their body is maintained at 30°C by their active flight muscles and their body is insulated by a thick layer of furry scales.

 

Moths can warm up their bodies by shivering (photo by Paul Billiet)

Moths can warm up their bodies by shivering

 

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