According to evolutionary and adaptive theories, animals tend to develop different behavioral strategies in order to maximize their fitness. Indeed, the optimal foraging theory stipulates that animals adopt certain strategies to maximize the energy ratio between acquisition and expenditure during foraging which is directly related to their growth and reproductive success. Thus, measuring and quantifying multiple key parameters, like energy expenditure, provides precious insights about animals’ behavior and ecology. In the majority of the vertebrates, locomotion is the major cost contributing to energy expenditure during the foraging period which can be estimated by the animal’s acceleration. Today, through technology advancements, acceleration is easily measured using miniature data logging tags attached to animals that incorporate three-axis accelerometers and magnetometers. Basically, the accelerometer measures the raw acceleration composed by the static acceleration (gravity: low frequency) and the dynamic acceleration (animal movement: high frequency). The main difficulty is extracting the dynamic acceleration from the raw acceleration, which is needed to estimate the energy expenditure. A widely used method for estimating animal acceleration generates a metric called ODBA (The Overall Dynamic Body Acceleration). ODBA is calculated by separating the low and high frequency from the raw acceleration with a running mean method or a low pass filter. OBDA assumes that the animal is not rotating. However, body rotation is normal with aquatic animal transiting and foraging. In this case, an extra acceleration signal is measured and added to the real dynamic acceleration. To avoid this problem, a new method called ELBA (Estimated Linear Body Acceleration) that uses a gyroscope in addition to the accelerometer was developed. Effectively, Ware et al. (in review) showed that ELBA estimates the animal’s speed more accurately than ODBA. As a continuation of that project, I wanted to find out the relationship between the animal energy expenditure and ELBA.
To investigate this relationship, we attached an Opentag Loggerhead Instruments device, incorporating an accelerometer, a magnetometer, and a gyroscope to the Steller sea lions (Eumetopias jubatus) housed at the UBC Open Water Research Station (Port Moody, British Columbia, Canada). Each sea lion is trained to dive from a respirometry dome at the surface to the feeding tubes at depths of up to 40 meters, then return to the floating dome, where oxygen consumption and carbon dioxide production is measured with gas analyzers. This provides an accurate estimation of energy expenditure.
Preliminary results showed a significant positive relationship between animal energy expenditure and its movement acceleration during dives. On the other side, the distinction between ELBA and ODBA in estimating the animal acceleration remains uncertain so far and requires further investigation.