This is bird note.

Long distance migration requires

long distance migration requires metabolic feats that dazzle the mind

and lots of fat. Tiny black pole warblers

double their weight in the lead up to migration. Wilson's fall ropes may put on

so much fat that they actually have to lose weight

to get their fat-loaded bodies into the air.

Chubby bar-tailed Godwits, normally very strong flyers,, may need a long running start to take off.

To store fat, birds may eat three times as much and forage over many more hours than normal as they prepare for long distance travel.

To process so much chow, a bird's stomach and intestines must physically grow in size.

A bird's liver, the organ that turns nutrients into fats,

might triple in size.

At the cellular level, equally impressive changes make it possible for a bird to draw energy from all that fat during long flights.

These include changes in fatty acids,

plus a big bump in the protein molecules that move fats

through the bloodstream.

And there's a surge in enzymes that hand off the fat to the muscles, thus fueling the strenuous work of flight.

If long migratory flights are amazing, what goes on inside a bird's body during those flights seems absolutely astonishing.

For Bird Note, I'm Michael Stein.