Balmy Birds

Birds and some mammals can change their temperature using their feathers or fur.

Have you seen 'big looking' cats or chickens on cold days? They may look double their usual size. Why is this? And what about animals that live in really cold conditions, such as polar bears? They can even swim for hours in almost frozen water. How is this possible?

You can explore the insulating ability of air using ice cubes.

1. Wrap an ice cube with bubble wrap (bubble wrap contains lots of air).
2. Put a bare ice cube next to it and warm both of them with a lamp.
3. Which ice cube melts first? Why?
4. Discuss the result together (it is about the insulation property of air.)

Simple explanation

Birds and mammals need to maintain a steady body temperature, so they must find a way to keep themselves warm. They cannot go out and buy a new coat during the winter or turn on the heating when it is cold outside.

There are different strategies for solving this problem. Most mammals have fur, and most birds have feathers. One strategy can be simply 'inflating' fur or feathers to trap more air, as air itself is a very good insulator.

Imagine that you're outside on a sunny day, wearing a black t-shirt and your friend is wearing a white t-shirt. After some time in the sun, you notice that your black t-shirt feels hotter than your friend's white t-shirt. This is because black surfaces absorb more heat than white ones. When sunlight hits a surface, it can be either reflected or absorbed. White surfaces reflect more sunlight, while black surfaces absorb more sunlight. When sunlight is absorbed by a surface, it gets converted into heat. So, if a black surface absorbs more sunlight, it will also absorb more heat, making it feel hotter to the touch than a white surface that reflects more sunlight and heat away.

A strategy, used by polar bears, is to have black skin and two layers of fur. The black skin absorbs the heat of the sun. The lower, dense layer of fur minimizes heat loss from the body, while the upper longer and coarser hairs protect the lower fur from injury.

More detailed explanation

Animals often use air to help them stay warm. They do this by keeping warm air next to their skin using their fur or feathers to trap it. Air trapped next to the skin is warmed by the body of the animal. Air is good at retaining warmth because its molecules are far apart from each other, making it harder for heat to be transferred and lost.

The upper layer of polar bears’ fur is hollow and oily, so it helps with  insulation. The oily layer keeps the lower layer dry and the hollow, air-filled fur helps block the transfer of heat and also makes swimming in water easier.

In the past, people commonly used the fur and feathers of animals as coats and blankets. We still do: fur coats and goose down jackets are common today. We’ve also learned how to create artificial fibers that are hollow, like polar bear fur, and insulating foams, which have lots of trapped air inside them.

A boy in the U.S.A. invented an inflatable coat which can be inflated in cold weather to increase its insulation properties, and deflated in warm weather so it does not get too hot (take a look). A company now makes a coat with a hand pump to change the amount of air trapped in the coat.

We use a lot of energy to heat and cool buildings. One of the best ways we can use less energy is to better insulate our homes and buildings. Air can be a great way to do this. Adding insulation to our walls and attics, and in between our window panes, can help us use less energy, reducing greenhouse gases, and making it easier to use clean, renewable energy sources.

Some STEAM opportunities include:

• Identify and compare suitability of everyday materials.
• Comparing the (insulation) properties of different materials.
• Asking questions and making observations.
• Carrying out simple tests.
• Making predictions.
• Using scientific evidence to answer a question.
• Apply learning to real world problems.
• Observing and raising questions about how different animals adapt.
• Analyse advantage and disadvantage of different adaptations/behaviours.