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RESEARCH PRODUCT

The insectivorous batPipistrellus nathusiiuses a mixed-fuel strategy to power autumn migration

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In contrast to birds, bats are possibly limited in their capacity to use body fat as an energy source for long migrations. Here, we studied the fuel choice of migratoryPipistrellus nathusii(approximate weight: 8 g) by analysing the stable carbon isotope ratio (δ13CV-PDB) of breath and potential energy sources. Breathδ13CV-PDBwas intermediate betweenδ13CV-PDBof insect prey and adipocyte triacylglycerols, suggesting a mixed-fuel use ofP. nathusiiduring autumn migration. To clarify the origin of oxidized fatty acids, we performed feeding experiments with captiveP. nathusii. After an insect diet, bat breath was enriched in13C relative to the bulk and fat portion of insects, but not deviating from the non-fat portion of insects, suggesting that bats oxidized exogenous proteins and carbohydrates, but not exogenous fatty acids. A feeding experiment with13C-labelled substrates confirmed these findings. In conclusion, migratoryP. nathusiioxidized dietary proteins directly from insects captured en route in combination with endogenous fatty acids from adipocytes, and replenished their body reserves by routing dietary fatty acids to their body reserves.