Fig. 1. Typical ¹³C isotope elimination curve from (A) Palestine sunbird Nectarinia osea and (B) starling Sturnus vulgarus. There was rapid incorporation of the isotope into the body bicarbonate pools and equilibrum was reached in all cases within 5 min in the sunbirds and 10 min in the starlings. The isotope was then gradually eliminated over the following 50 min until it approached the pre-measured background level of ¹³C.