Carbon isotope ratios in exhaled CO2 can be used to determine not just present, but also past diets in birds
2002
Hatch, K.A. | Pinshow, B. | Speakman, J.R.
We show that an animal's past and present diet can be distinguished through the delta13C of exhaled CO2. The exhaled delta13C of 12 pigeons fed solely corn (a C4 plant) for 30 days was -13.63 ppt (+/-0.30). We then fed six pigeons wheat (a C3 plant) and continued to feed the other six corn. After 48 h the exhaled delta13C from the corn-fed pigeons was unchanged; that from the wheat-fed pigeons was -20.5 ppt. We then fasted three of the wheat-fed pigeons for 3 days, after which their exhaled delta13C was -14.96 ppt, while it was -13.57 ppt in corn-fed pigeons, and -22.22 ppt 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 delta13C alone, if the initial breath sample is followed by a fasted breath sample, without harming the animal or having to recapture it successively.
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