Hummidees, Jaybins, and Ravoons
A Lesson About Volume, Surface Area and Body Heat

Background
How much work does a bird's body have to do to keep warm? Create your own "cubic birds" that resemble the size of some birds we already know to explore this question!

When you touch your face, you can feel the heat your body is producing leaking out into the air, or onto your hand. Your muscles and blood and organs produce the heat.

The amount of heat a warm-blooded animal produces is related to its body's volume. The bigger the body's volume, the more of these heat-producing tissues fit inside. Fur or feathers help hold heat in, but some body heat always escapes.

 The amount of heat a body loses is related to its surface area--how much surface it has where heat can leak out.
 The tinier something is the larger its surface area compared to its volume, and so the more heat it loses compared to the heat it produces.

The simplest way to understand this is with blocks that are one cubic inch in size.

Before you begin, help students to understand the concepts of volume and surface area. A block that is one inch on every edge has a volume of one cubic inch. The block's six sides give it a surface area of six square inches. When students understand the concept of volume and surface area, continue with the directions below.

 NOTE: For the following demonstration, you can use ready-made blocks that are one cubic inch, or use our pattern to have students create 44 individual paper blocks. Or, you can simply reason through the lesson without using blocks.

Activity

1. Make (or picture) a pretend tiny cubic bird that's one cubic inch in size. We'll call it a "hummidee."

2. Put 8 of your cubic-inch blocks together to make a bigger bird block. What is its volume? (8 cubic inches) What is its surface area? (24 square inches) This medium-sized bird is your "jaybin."

3. Now put 27 blocks together to make an even bigger bird block. What is its volume? (27 cubic inches) Its surface area? (54 square inches). This big bird will be called a "ravoon."

4. Discuss and compare the amount of heat produced by each of the three birds.

How much space does each of these "birds" have for producing heat? (The hummidee produces heat in 1 cubic inch of space, the jaybin in 8 cubic inches of space, and the ravoon in 27 cubic inches of space.) Can you see how the jaybin can produce 8 times more heat than the hummidee, and the ravoon 27 times more than the hummidee? (Heat production is actually more complicated than this, but the relationships are pretty close.)

Discussion
1. Talk about total surface area of heat that can be lost for each of the three birds. Ask,

• Over how many square inches of skin does the hummidee lose heat? (6 square inches)
• Over how many square inches of skin does the jaybin lose heat? (24 square inches)

2. How many times more heat does the jaybin lose than the hummidee? (Over 4 times the amount of heat)

But think about this! Because the jaybin produces 8 times as much heat as the hummidee, it keeps more of its heat inside than the hummidee does.

3. Over how many square inches of skin does that huge ravoon lose heat? (Over 54 square inches of skin) That's 9 times the amount of heat the hummidee loses. But the ravoon produces 27 times the amount of heat as the hummidee, so this big bird is still way ahead!
4. What strategies might tiny hummingbirds have to make more body heat--and to make the most of the body heat they DO produce? (Tiny birds need to shiver so much more than larger birds. Shivering makes their muscles do extra work to produce more heat than larger birds need. Hummingbirds also build such tiny, tight nests for a good reason. A tiny nest helps to hold in a hummer's body heat so the babies inside their eggs can warm up and develop without wasting the mother's heat and energy.)

 Hummingbird (Hummidee) Blue Jay (Jaybin) Courtesy Anne Cook Raven (Ravoon) Courtesy Chan Robbins