"Can energy expenditure of free-ranging kittiwakes be estimated by body acceleration?"

Abstract

Abstract The way energy is used and acquired are fundamental questions in animal biology and figure greatly into conservation of a species. Accurate estimates of energy expenditure are critical in understanding how successful animals are throughout their lifespan and in quantifying population energy budgets and their role and impact on an ecosystem. Two methods have been commonly used to estimate daily energy expenditure (DEE) of free ranging animals: the doubly labeled water (DLW) method and the heart rate method. A third, less invasive method uses activity data captured by accelerometers. The recent development of miniature accelerometer data loggers have made it possible to use this method on small free-ranging animals; however, the method needs to be validated on the species of interest. Believed to be the most numerous gull species, the black-legged kittiwake (Rissa tridactyla) is well studied in the Arctic and therefore a valuable candidate for elucidating alternative methods of energy expenditure. We deployed miniature accelerometer data loggers on eight breeding kittiwakes in Kongsfjord, Svalbard, and recorded body acceleration continuously over a three day period. From recorded acceleration in three axes, overall dynamic body acceleration (ODBA) was calculated for each bird. To validate accelerometry, we estimated the birds’ energy expenditure using the DLW method. In addition, a control group of twelve birds was only treated with the DLW method to determine if the deployment of the loggers had an effect on the energy expenditure of the birds. Using the DLW method, we found the mean DEE for birds with and without loggers was 1147 kJ/day (±217 SD) and 974 kJ/day (±219 SD), respectively. The loggers were not found to have an effect on DEE (t18 = 1.733, p = 0.1), nor was there any correlation between calculated ODBA and estimated DEE (r= -0.174, t6= -0.432, p= 0.681) for the kittiwakes studied. With the removal of an apparent outlier, the correlation between the ODBA and estimated DEE was strengthened and evidence of a significant effect of loggers on DEE was revealed. The question that remains unanswered is if kittiwakes have a correlation between ODBA and DEE. It is possible that locomotion does perhaps not constitute a large enough part of EE in kittiwakes to be reflected accurately by ODBA. However methodical errors should not stand in the way of the promise of accelerometry as an accurate method of measuring energy expenditure in free-ranging seabirds.