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It has been proposed that water loss in flight of migratory birds under high evaporative conditions can be offset by the production of water through increased protein catabolism.  Indeed, oxidation of protein may supply 7-times more water/kJ than fat. However, the lack of a relative increase in protein catabolism over that of fat during long flights is indicative of alternative processes that may take place in birds under long and strenuous flights.  Among them, release of stress hormones (which increase both protein and fat catabolism) and increased protein catabolism triggered by increased oxidative damage to muscle proteins elicited by phosphorylating mitochondria, processes not necessarily linked to water deprivation.