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 warmblooded animal produces is related to its body's volume.
The bigger the body's volume, the more of these heatproducing 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 areahow
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.
Click
on image for Cubic Inch Block pattern idea

NOTE:
For the following demonstration, you can use readymade 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
 Make
(or picture) a pretend tiny cubic bird that's one cubic inch in size.
We'll call it a "hummidee."
 Put 8
of your cubicinch blocks together to make a bigger bird block. What
is its volume? (8 cubic inches) What is its surface area? (24 square
inches) This mediumsized bird is your "jaybin."
 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."
 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!
Hummingbird
nest
Courtesy of
Dorothy Edgington

4. What strategies
might tiny hummingbirds have to make more body heatand 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.)
