Incorporation of the deuterium isotopic value of rainwater in the tissues of producers and primary consumers, The

Ecologists use a variety of extrinsic markers (such as bands and radio transmitters) to track the movements of migratory birds with limited success. One alternative technique utilizes an intrinsic marker, the hydrogen isotope composition (δD) of bird tissues. Flight feathers are molted and regrown during the summer months and are therefore assumed to incorporate the δD value of local precipitation of the area in which they were grown. Controlled feeding experiments, however, have shown that only ~20% of the hydrogen in a feather is derived from ingested drinking water, with the remainder sourced from diet. To learn more about how hydrogen isotopes are incorporated into food webs, we grew cabbage plants using water with differing δD values. We then subjected each plant to a primary consumer (caterpillars) to characterize how δD values are transferred across links in food webs. Isotopic analysis of both primary producer and consumer will determine if and how much the precipitation deuterium levels differ from those of a bird's diet. This information may be used to evaluate the accuracy of this tracking method, an essential step toward understanding the ecology of migratory birds.