文档介绍：Oecologia (2004) 141: 1 – 6 DOI -004-1643-y METHODS Scott A. Carleton .Blair O. Wolf . Carlos Martinez del Rio Keeling plots for hummingbirds: a method to estimate carbon isotope ratios of respired CO 2in small vertebrates Received: 23 October 2003 / Accepted: 26 May 2004 / Published online: 11 August 2004 # Springer-Verlag 2004 Abstract The carbon position of an animal ’ s breath reveals position of the nutrients that it catabolizes for energy. Here we describe the use of Keeling plots, a method widely applied in ecosystem ecology, to measure the δ 13C of respired CO 2of small vertebrates. We measured the δ 13C of Rufous Humming- birds ( Selasphorus rufus ) in the laboratory and of Mourn- ing ( Zenaida macroura ) and White-winged ( Z. asiatica ) Doves in the field. In the laboratory, when hummingbirds were fed a sucrose based C3 diet, the δ 13C of respired CO 2 was not significantly different from that of their diet ( δ 3 diet ). The δ 13C of respired CO 2for C3 fasted birds was slightly, albeit significantly, depleted in δ 13C relative to δ 3 diet . Six hours after birds were shifted to a sucrose based C4 diet, the position of their breath revealed that birds were catabolizing a mixture of nutrients derived from both the C3 and the C4 diet. In the field, the δ 13C of respired CO 2from Mourning and White- winged Doves reflected that of their diets: the CAM sag