Breath analyses are not just for drunk drivers. A form of a breath test that measures stable isotopes (as opposed to radioactive isotopes) of carbon can be used to determine which fuel animals burn to supply various energetic needs. This is possible because as various fuels are metabolized, they create carbon dioxide that is exhaled as a waste product. Measurement of the stable isotope ratio of carbon-13 in the breath tells researchers which fuel was burned in the body. This type of a test was used to determine what fuels bats utilize to support the energetic needs of flight.
To establish a baseline, researchers measured the ratio of carbon-13 in the breath of fasted resting lesser bulldog bats (Noctilio albiventris; shown above in image from article) as well as resting bats that had just eaten an insect-rich meal. These carbon-13 ratios were then compared to free-ranging bats just emerging from their roosts or after having eaten insect-rich diets while flying. If these bats were supplying their high energetic flight with stored fuels, then the carbon-13 ratio would match that of the fasted resting bats. In contrast, if they were using up their natural stores and burning mainly fuels obtained from their diet while flying, then the carbon-13 ratio of their breath should become the same as that of their diet.
By analyzing bat breath, lead researcher Christian Voigt (Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany) has discovered that the lesser bulldog bats are indeed able to meet the high energetic demands of flight by burning recently eaten insects for fuel. This is fascinating because most animals fuel exercise with stored forms of nutrients, like glycogen (stored sugar), fats or proteins. It is not often that an animal can burn fuel they have ingested while exercising, much less hard to digest fuels like insects, which are rich in protein and fat. It is amazing these bats can burn such complex fuels so efficiently to meet immediate needs. This is in contrast to the fasted resting bats that burned predominantly stored fats for energy.
Voigt CC, Sorgel K, Dechmann DKN. Refueling while flying: Foraging bats combust food rapidly and directly to power flight. Ecology 91: 2908-2917, 2010.