Validating accelerometry estimates of energy expenditure across behaviours using heart rate data in a free-living seabird.

Francis Daunt,Adam Butler,Sarah Burthe,Olivia Hicks,Charles Bishop,Jonathan A. Green

doi:10.1242/jeb.152710

Abstract

ABSTRACTTwo main techniques have dominated the field of ecological energetics: the heart rate and doubly labelled water methods. Although well established, they are not without their weaknesses, namely expense, intrusiveness and lack of temporal resolution. A new technique has been developed using accelerometers; it uses the overall dynamic body acceleration (ODBA) of an animal as a calibrated proxy for energy expenditure. This method provides high-resolution data without the need for surgery. Significant relationships exist between the rate of oxygen consumption (V̇O2) and ODBA in controlled conditions across a number of taxa; however, it is not known whether ODBA represents a robust proxy for energy expenditure consistently in all natural behaviours and there have been specific questions over its validity during diving, in diving endotherms. Here, we simultaneously deployed accelerometers and heart rate loggers in a wild population of European shags (Phalacrocorax aristotelis). Existing calibration relationships were then used to make behaviour-specific estimates of energy expenditure for each of these two techniques. Compared with heart rate-derived estimates, the ODBA method predicts energy expenditure well during flight and diving behaviour, but overestimates the cost of resting behaviour. We then combined these two datasets to generate a new calibration relationship between ODBA and V̇O2 that accounts for this by being informed by heart rate-derived estimates. Across behaviours we found a good relationship between ODBA and V̇O2. Within individual behaviours, we found useable relationships between ODBA and V̇O2 for flight and resting, and a poor relationship during diving. The error associated with these new calibration relationships mostly originates from the previous heart rate calibration rather than the error associated with the ODBA method. The equations provide tools for understanding how energy constrains ecology across the complex behaviour of free-living diving birds.

Highlights

Energy is a central currency in the behaviour and physiology of animals (Butler et al, 2004)
Relatively few studies have investigated whether overall dynamic body acceleration (ODBA) represents a robust proxy for energy expenditure across natural behaviours at high resolution in free-ranging birds (Duriez et al, 2014; Weimerskirch et al, 2016)
We found a good relationship between ODBA and VO2

Summary

Introduction

Energy is a central currency in the behaviour and physiology of animals (Butler et al, 2004). Received 2 November 2016; Accepted 28 February 2017 energy to allocate to maximising fitness and life history is constrained by energetics (Brown et al, 2004). Such constraints can result in trade-offs between survival and reproduction (Brown et al, 2004; Halsey et al, 2009). We need to quantify how energy is allocated and partitioned to different behaviours and processes to understand how life-history decisions are made (Green et al, 2009; Tomlinson et al, 2014), and improve the predictive power of species distribution or population dynamic models (Buckley et al, 2010)

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