Counting calories in cormorants: dynamic body acceleration predicts daily energy expenditure measured in pelagic cormorants

Abstract

The integral of the dynamic component of acceleration over time has been proposed as a measure of energy expenditure in wild animals. We tested that idea by attaching accelerometers to the tails of freeranging pelagic cormorants (Phalacrocorax pelagicus) and simultaneously estimating energy expenditure using doubly labelled water. Two different formulations of dynamic body acceleration, [vectorial and overall DBA (VeDBA and ODBA)], correlated with mass-specific energy expenditure (both R 2 =0.91). VeDBA models combining and separately parameterizing flying, diving, activity on land and surface swimming were consistently considered more parsimonious than time budget models and showed less variability in model fit. Additionally, we observed evidence for the presence of hypometabolic processes (i.e. reduced heart rate and body temperature; shunting of blood away from non-essential organs) that suppressed metabolism in cormorants while diving, which was the most metabolically important activity. We concluded that a combination of VeDBA and physiological processes accurately measured energy expenditure for cormorants.

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

“…The R 2 value for our overall model is comparable but slightly lower than that for studies comparing partial dynamic body acceleration and energy expenditure by the doubly labelled water method in the wild [ R 2 =0.73 in thick billed murres (Elliott et al, 2013) and R 2 =0.91 in pelagic cormorants (Stothart et al, 2016)] and consistently lower than measurements obtained on treadmills in the laboratory [ R 2 =0.81–0.93 for four bird and mammal species (Halsey et al, 2009)] and experimental dive tanks [ R 2 =0.83 for green turtles (Enstipp et al, 2011)]. The R 2 value from this study is expected to be lower than those from previous studies, as the ODBA values were not daily averages as in most previous studies, but instead were calculated over shorter time scales of behavioural bouts (Elliott, 2016; Green, 2011).…”

“…The high temporal resolution of the calibration in this study compared with that of previous studies (Elliott et al, 2013; Jeanniard-du-Dot et al, 2016; Stothart et al, 2016) allows the more complex differences in energy expenditure between behaviours and resultant differences in predictive estimation equations between different behaviours to be quantified. All three behavioural modes had different predictive equations when estimating V̇ O 2  from ODBA.…”

“…Given the importance of quantifying the energetic cost of behaviours to understand the fitness consequences in wild populations, it is crucial to validate the accelerometry technique across the natural range of locomotory modes in free-living animals. Validations exist using the doubly labelled water method, which show that ODBA predicts daily averages of energy expenditure (Elliott et al, 2013; Jeanniard-du-Dot et al, 2016; Stothart et al, 2016). However, as the accelerometry technique has developed and is now able to discern and estimate energy expenditure across fine scale behaviours, it is timely to validate these measurements with a technique with equally high resolution (Green et al, 2009).…”

Tracking Cairns: Biologging Improves the Use of Seabirds as Sentinels of the Sea

“…Accelerometers provide direct estimates of prey capture rates and energy expenditure over the entire range of food supply variation (Wilson et al, 2006;Watanabe and Takahashi, 2013;Stothart et al, 2016), and coupling GPS locations with accelerometer data could allow the modeling of energy landscapes, with net energy intake peaks corresponding to regions of high food supply. Regardless, biologgers provide a variety of potential foraging parameters, and we suggest that studies examine multiple parameters simultaneously.…”

Correlations of metabolic rate and body acceleration in three species of coastal sharks under contrasting temperature regimes

“…Elliott et al, 2012;Stothart et al, 2016;Roos et al, 2016). This type of concomitant validation in the field is unfortunately not possible for water-breathing taxa; instead, calibrations in the laboratory represent the most comprehensive validation possible for the method in fish.…”