3/30/14 and 3/31/14: This week on "Fieldnotes:" "Mammal Insulation," by Carol Alette.
"Sea otters waterproof their fur with oil from their skin, and then roll in the water to trap air bubbles in the fur for insulation and buoyancy. Whales and dolphins, on the other hand, are better insulated by blubber than fur because they dive deeply enough that water pressure would flatten hair against the body and minimize its insulating qualities. Another familiar heating system is simply to grow more hair in the winter. A deer's winter coat is as much as four times deeper than its summer one."