Combining Accelerometers and Magnetometers to Better Estimate Energy Expenditure in Albatross Flight

Understanding mechanistic links between climate-driven variability in fluid flow, animal movement, energetics, and population processes is a critical, yet often overlooked, component of the biological impacts of climate change. Soaring seabirds that rely on wind to reach distant foraging grounds may be particularly impacted by changes in global patterns of wind, and to project future effects of climate change on seabird populations, it is essential to understand how wind influences flight efficiency. Here, we evaluate the relationship between energy expenditure (EE) and wind conditions for two species of albatross from the north Pacific Ocean. Biologging devices were deployed on adult black-footed (Phoebastria nigripes, n=10) and Laysan (P. immutabilis, n=15) albatross breeding on Midway atoll in 2019. We used a combination of GPS, accelerometer, and magnetometer tags to record positions and high-resolution flight behavior. Satellite wind data along tracks was used to characterize wind conditions encountered by foraging albatross. We used overall dynamic body acceleration (ODBA) as a proxy of EE to measure the relationship between EE and wind conditions along each albatross track during different flight modes. Because albatross fly using both dynamic soaring and flapping flight, we also evaluated how ODBA relates to different flight modes. We found ODBA to more accurately reflect EE in flapping flight than in dynamic soaring, and we present alternative metrics derived from a combination of accelerometers and magnetometers that have potential to more accurately reflect EE during dynamic soaring than ODBA from accelerometers alone. Future work will incorporate heart-rate loggers to both evaluate and validate the accuracy of ODBA and alternative metrics as proxies of EE during dynamic soaring. Validated metrics of EE will then be used to develop a mechanistic understanding of how wind variability impacts albatross flight behavior and flight efficiency.