The telltale heart: A non-invasive method to determine the energy expenditure of incubating great cormorants Phalacrocorax carbo carbo

We studied the energetics of incubating Great Cormorants Phalacrocorax carb o carbo via heart rate and respirometric measurements performed in captive and free-living animals. We applied a modified heart beat frequency (HR) mo nitor built for use in human athletics as well as respirometry for measurem ents in four captive-bred cormorants at Neumunster Zoo, Germany. The obtain ed data were used to model the relationship between HR and metabolic rate ( MR). The resulting correlations were MR (W kg(-0.723)) = 4.76 + 0.01HR (bpm ) during daytime and MR (W kg(-0.723)) = 2.33 + 0.03HR (bpm) at night. Furt hermore, the heart beat frequencies of 5 free-living, incubating cormorants at the Chausey Islands, France, were measured acoustically using artificia l eggs while the activities at the nest were observed via video. HR-MR mode ls established in the captive animals were used to determine the activity-d ependent energy expenditure in these free-living cormorants. The Median MR was 5.08 W kg(-0.723) at night, 6.06 W kg(-0.723) while resting and sleepin g during daytime, 6.20 W kg(-0.723) during preening, gular nutter and unres t and 6.47 W kg(-0.723) during nest building. In resting birds we found a n octurnal reduction in the energy expenditure of 16 %. Our method for measur ement of heart beat frequency appears promising as a technique for determin ation of HR with minimal restraint to the animal.