Lisa, I'll try and explain what I think Burt meant. Many organisms,
given an excess of carbohydrate in their diet, can convert it inot fat
for storage. The conversion is not as efficient as the fat to fat
conversion; there is some energy loss in the transformation. But, given
enough carbohydrate it is quite possible to still become fat. Fat is
more efficient to store in two ways. It has a higher energy content per
gram, about 2.5 times more. Also, stored carbohydrate, like glycogen,
also binds large amounts of water so that storing 1 pound of carbohydrate
may also mean storing 2-3 poounds of water.

Back to birds-hummingbirds are an excellent example. A ruby throat can
only cross the Gulf by storing a lot of energy as fat, even though they
may have synthesized much of this fat from sugars. Market hunters in the
early days of shorebird hunting mentioned shorebirds-I cant remember the
species-splitting on hitting the ground due to the large amount of stored
fat.

Jim Neitzel