> [Why are migratory birds able to do such long distance flights?] Studies in insect flight muscle found that ATP is synthesized when the muscle is (passively) stretched; i suppose it happens in birds too. Studies of nerves show that after heat is emitted during activity, heat is absorbed during recovery, i.e. The nerve slightly refrigerates its surroundings. The absorption of heat (besides preventing over-heating) as ATP is resynthesized would make the usual Expectations about chemical energy and work less applicable.