While deploring the calories I was ingesting in the form of peanut butter, I was reminded how vital high caloric value can be to migratory birds. I have read that the hummingbirds what cross the Gulf of Mexico from Florida to the Yucatan peninsula store a special fat with 18 cal/gm.
Human fat is 9cal/gm if I remember correctly.
Then there is the godwit with migrates 7,000 miles from Alaska nonstop to New Zealand.I wonder how many miles per gm of fat they get.