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First published online June 27, 2008
Journal of Experimental Biology 211, 2233-2238 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.018523
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Stable carbon isotopes in exhaled breath as tracers for dietary information in birds and mammals

Christian C. Voigt1,*, Leonie Baier2, John R. Speakman3 and Björn M. Siemers2

1 Evolutionary Ecology Research Group, Leibniz Institute for Zoo and Wildlife Research, Alfred-Kowalke-Straße 17, D-10315 Berlin, Germany
2 Max-Planck-Institute for Ornithology, Sensory Ecology Group, Eberhard-Gwinner-Straße, 82319 Seewiesen, Germany
3 Aberdeen Centre for Energy Regulation and Obesity, School of Biological Sciences, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, UK

* Author for correspondence (e-mail: voigt{at}izw-berlin.de)

Accepted 7 May 2008

The stable carbon isotope ratio of exhaled CO2 ({delta}13Cbreath) reflects the isotopic signature of the combusted substrate and is, therefore, suitable for the non-invasive collection of dietary information from free-ranging animals. However, {delta}13Cbreath is sensitive to changes in ingested food items and the mixed combustion of exogenous and endogenous substrates. Therefore, experiments under controlled conditions are pivotal for the correct interpretation of {delta}13Cbreath of free-ranging animals. We measured {delta}13Cbreath in fasted and recently fed insectivorous Myotis myotis (Chiroptera) to assess the residence time of carbon isotopes in the pool of metabolized substrate, and whether {delta}13Cbreath in satiated individuals levels off at values similar to the dietary isotope signature ({delta}13Cdiet) in insect-feeding mammals. Mean {delta}13Cbreath of fasted individuals was depleted by –5.8{per thousand} (N=6) in relation to {delta}13Cdiet. After feeding on insects, bats exchanged 50% of carbon atoms in the pool of metabolized substrates within 21.6±10.5 min, which was slower than bats ingesting simple carbohydrates. After 2 h, {delta}13Cbreath of satiated bats levelled off at –2.6{per thousand} below {delta}13Cdiet, suggesting that bats combusted both exogenous and endogenous substrate at this time. A literature survey revealed that small birds and mammals metabolize complex macronutrients at slower rates than simple macronutrients. On average, {delta}13Cbreath of fasting birds and mammals was depleted in 13C by –3.2±2.0{per thousand} in relation to {delta}13Cdiet. {delta}13Cbreath of satiated animals differed by –0.6±2.3{per thousand} from {delta}13Cdiet when endogenous substrates were not in isotopic equilibrium with exogenous substrates and by +0.5±1.8{per thousand} (N=6 species) after endogenous substrates were in isotopic equilibrium with exogenous substrates.

Key words: bats, dietary preferences, exogenous substrate, fat, metabolism, stable isotopes






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