Abstract
Energy drives behaviour and life history decisions, yet it can be hard to measure at fine scales in free-moving animals. Accelerometry has proven a powerful tool to estimate energy expenditure, but requires calibration in the wild. This can be difficult in some environments, or for particular behaviours, and validations have produced equivocal results in some species, particularly air-breathing divers. It is, therefore, important to calibrate accelerometry across different behaviours to understand the most parsimonious way to estimate energy expenditure in free-living conditions. Here, we combine data from miniaturised acceleration loggers on 58 free-living Adélie penguins with doubly labelled water (DLW) measurements of their energy expenditure over several days. Across different behaviours, both in water and on land, dynamic body acceleration was a good predictor of independently measured DLW-derived energy expenditure (R2 = 0.72). The most parsimonious model suggested different calibration coefficients are required to predict behaviours on land versus foraging behaviour in water (R2 = 0.75). Our results show that accelerometry can be used to reliably estimate energy expenditure in penguins, and we provide calibration equations for estimating metabolic rate across several behaviours in the wild.
Highlights
Energy drives behaviour and life history decisions, yet it can be hard to measure at fine scales in free-moving animals
doubly labelled water (DLW)-estimated mass-specific energy expenditure was positively correlated with both measures of DBA: mean vectoral dynamic body acceleration (VeDBA) (R2 = 0.72, t47 = 10.705, p < 0.0001; Fig. 1) and mean overall dynamic body acceleration (ODBA) (R2 = 0.72 t47 = 10.73, p < 0.0001)
We show that dynamic body acceleration predicts energy expenditure, measured via doubly labelled water, in free-living birds inhabiting an extreme environment, and across several behavioural modes including prolonged diving in sub-zero water
Summary
Energy drives behaviour and life history decisions, yet it can be hard to measure at fine scales in free-moving animals. Accelerometry has proven a powerful tool to estimate energy expenditure, but requires calibration in the wild This can be difficult in some environments, or for particular behaviours, and validations have produced equivocal results in some species, air-breathing divers. It is, important to calibrate accelerometry across different behaviours to understand the most parsimonious way to estimate energy expenditure in free-living conditions. No surprise that the two studies in which no relationship was found betweenV O2 and DBA, were conducted in cold-water homeotherms that operate both in the air and in water[34,35] In this context, Antarctic penguins, as flightless birds, provide an interesting model for validating the accelerometry technique in the wild. (1) Can accelerometry be used to estimate energy expenditure in free living and diving Adélie penguins Pygoscelis adeliae? And if so, (2) do calibration equations differ between behaviours or mediums (air or water)? That is to say, what is the most parsimonious way to estimate overall energy expenditure of wild Adélie penguins using accelerometry?
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