Carbon isotope ratios in exhaled CO2 can be used to determine not just present, but also past diets in birds

K. A. Hatch, B. Pinshow, J. R. Speakman

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


We show that an animal's past and present diet can be distinguished through the δ13C of exhaled CO2. The exhaled δ13C of 12 pigeons fed solely corn (a C4 plant) for 30 days was -13.63‰ (±0.30). We then fed six pigeons wheat (a C3 plant) and continued to feed the other six corn. After 48 h the exhaled δ13C from the corn-fed pigeons was unchanged; that from the wheat-fed pigeons was -20.5‰. We then fasted three of the wheat-fed pigeons for 3 days, after which their exhaled δ13C was -14.96‰, while it was -13.57‰ in corn-fed pigeons, and -22.22‰ in pigeons that continued on wheat. Thus, we could infer diet from the 13C/12C ratios of exhaled CO2. Significantly, breath samples from fasted pigeons also revealed that they had eaten corn when their lipid stores were formed. We also showed that the change in the 13C/12C of exhaled CO2 had a half-life of approximately 3.5 h, and a time constant of approximately 6.7 h. Thus one can infer past and present diet from exhaled δ13C alone, if the initial breath sample is followed by a fasted breath sample, without harming the animal or having to recapture it successively.

Original languageEnglish
Pages (from-to)263-268
Number of pages6
JournalJournal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology
Issue number3
StatePublished - 1 Dec 2002


  • Breath
  • Carbon dioxide
  • Diet
  • Dietary history
  • Stable isotopes

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Biochemistry
  • Physiology
  • Animal Science and Zoology
  • Endocrinology


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