Minus 3: Baby Cradle
This nest is exactly big enough to hold two tiny eggs and the mother hummer. The eggs are snuggled in by the
nest's soft sides and bottom and, when she's incubating, by the mother's tummy. She must share her body heat with
her eggs, and can't afford to let any heat leak out into the air.
Q: Why do tiny birds like hummingbirds and chickadees lose body heat
so much more easily than large birds
like ravens and loons? (Answer below photo.)
A: The amount of heat a warm-blooded animal produces
is related to its body's volume. The heat is produced by the animal's
muscles and blood and organs. The bigger the volume of the body, the
more of these heat-producing tissues fit inside.
How much heat a body loses is related to its surface area, which means
how much skin it has where heat leaks out. Fur or feathers help hold
heat inside a body, but some heat always escapes. (When you touch your
face, you can feel the heat your body produced leaking out into the
air, or onto your hand.)
This is why 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. And it's why hummers build such a tiny, tight nest.
A tiny nest holds in their body heat so the babies inside their eggs
can warm up and develop without wasting the mother's heat and energy.