Carrier Pigeons

PROF. MAREY states in his “Animal Mechanism,” p. 214, “that a bird which has traversed in a single flight a distance of fifty leagues (which it seems to do without taking any food) weighs only a few grammes less than at its departure.” I shall be grateful to any of your readers who will inform me where evidence of this is to be found. The enormous amount of food consumed by birds would seem to show that the processes of loss and repair go on in their bodies with great rapidity.