Language：English   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Various environmental oceanic factors, such as ocean waves, affect seabird ecology; ocean waves are important, as most flying seabirds must land on ocean surfaces for foraging. However, the global ocean wave observation network is spatiotemporally poor compared to other parameters; fine-scale information on wave conditions is limited, and the influence of wave conditions on seabirds has not been quantitatively studied. In this study, a method was developed to estimate ocean waves from the fine-scale motions of seabirds floating on the sea surface, as recorded by a global positioning system (single-point positioning). Ocean wave parameters, estimated from streaked shearwater around the eastern ocean of Japan, strongly corresponded with the observation results of a buoy, with an accuracy of <0.3 m for wave heights of 1.0-2.5 m. Furthermore, wave height estimated from streaked shearwaters and wandering albatrosses around the southern Indian Ocean significantly correlated with hindcast-model values. Bird-based wave observation methods are valuable not only in seabird ecology but also in oceanography as an in-situ observation system. Based on the results of bird-based wave observations, the preferences of wandering albatrosses under various wave conditions were further examined. Anecdotal studies suggest that seabirds prefer low-wave conditions to forage in because of prey visibility; however, wandering albatrosses landed on the sea surface randomly, even on very high waves (5-6 m), revealing their tolerance to ocean surface conditions. Considering the effect of environmental factors on marine animals, increased inclusion of previously ignored parameters in analysis, such as ocean waves, is essential.

DOI： 10.1016/j.pocean.2021.102713

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：FUJI TECHNOLOGY PRESS LTD  

The study demonstrates the versatility of integration of inertial navigation and global navigation satellite system (GNSS) with its unique application to seabird biologging. Integrated navigation was originally developed in the field of aerospace engineering, which requires accurate and reliable position, velocity, and attitude information for the guidance and control of aircraft and spacecraft. Due to its high performance and recent progress of sensor development, integrated navigation has been widely used not only in aerospace but also in many fields represented by land and marine vehicles. One of its ultimate applications under the constraint on the size and power consumption of devices is this study. Seabird biologging involves attaching a logging device onto a seabird for scientific purposes to understand its biomechanics, behavior, and so on. Design restrictions for the device include several tens of grams mass, several tens of millimeters in length, and several tens of milliamperes of power consumption. It is more difficult to maintain the accuracy of such a device than applications to an artificial vehicle. This study has shown that integrated navigation is a feasible solution for such extreme applications with two examples: biologging for wandering albatrosses and great frigatebirds. Furthermore, it should be stressed that the navigation captured the world's first data of their detailed trajectories and attitudes in their dynamic and thermal soarings. For completeness, the navigation algorithm, simulation results to show the effectiveness of the algorithm, and the logging devices attached to bird are also described.

DOI： 10.20965/jrm.2021.p0526

Web of Science

DOI： 10.3389/fmars.2019.00326

Language：English   Publishing type：Research paper (scientific journal)  

Central place foraging theory (CPF) has been used to predict the optimal patch residence time for air-breathing marine predators in response to patch quality. Humpback whales (Megaptera novaeangliae) forage on densely aggregated prey, which may induce drastic change in prey density in a single feeding event. Thus, the decision whether to leave or stay after each feeding event in a single dive in response to this drastic change, should have a significant effect on prey exploitation efficiency. However, whether humpback whales show adaptive behavior in response to the diminishing prey density in a single dive has been technically difficult to test. Here, we studied the foraging behavior of humpback whales in response to change in prey density in a single dive and calculated the efficiency of each foraging dive using a model based on CPF approach. Using animal-borne accelerometers and video loggers attached to whales, foraging behavior and change in relative prey density in front of the whales were successfully quantified. Results showed diminishing rate of energy intake in consecutive feeding events, and humpback whales efficiently fed by bringing the rate of energy intake close to maximum in a single dive cycle. This video-based method also enabled us to detect the presence of other animals around the tagged whales, showing an interesting trend in behavioral changes where feeding duration was shorter when other animals were present. Our results have introduced a new potential to quantitatively investigate the effect of other animals on free-ranging top predators in the context of optimal foraging theory.

DOI： 10.1371/journal.pone.0211138

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATL ACAD SCIENCES  

Ocean surface winds are an essential factor in understanding the physical interactions between the atmosphere and the ocean. Surface winds measured by satellite scatterometers and buoys cover most of the global ocean; however, there are still spatial and temporal gaps and finer-scale variations of wind that may be overlooked, particularly in coastal areas. Here, we show that flight paths of soaring seabirds can be used to estimate fine-scale (every 5 min, similar to 5 km) ocean surface winds. Fine-scale global positioning system (GPS) positional data revealed that soaring seabirds flew tortuously and ground speed fluctuated presumably due to tail winds and head winds. Taking advantage of the ground speed difference in relation to flight direction, we reliably estimated wind speed and direction experienced by the birds. These bird-based wind velocities were significantly correlated with wind velocities estimated by satellite-borne scatterometers. Furthermore, extensive travel distances and flight duration of the seabirds enabled a wide range of high-resolution wind observations, especially in coastal areas. Our study suggests that seabirds provide a platform from which to measure ocean surface winds, potentially complementing conventional wind measurements by covering spatial and temporal measurement gaps.

DOI： 10.1073/pnas.1523853113

Web of Science

Publishing type：Research paper (scientific journal)   Publisher：The Royal Society  

The foraging strategy of many animals is thought to be determined by their past experiences. However, few empirical studies have investigated whether this is true in diving animals. We recorded three-dimensional movements and mouth-opening events from three Antarctic fur seals during their foraging trips to examine how they adapt their behaviour based on past experience—continuing to search for prey in the same area or moving to search in a different place. Each dive cycle was divided into a transit phase and a feeding phase. The linear horizontal distance travelled after feeding phases in each dive was affected by the mouth-opening rate during the previous 244 s, which typically covered two to three dive cycles. The linear distance travelled tended to be shorter when the mouth-opening rate in the previous 244 s was higher, i.e. seals tended to stay in the same areas with high prey-encounter rates. These results indicate that Antarctic fur seals follow decision-making strategies based on the past foraging experience over time periods longer than the immediately preceding dive.

DOI： 10.1098/rsbl.2015.0227

Other Link： https://royalsocietypublishing.org/doi/full-xml/10.1098/rsbl.2015.0227

Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1111/1365-2656.12346

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physreve.88.032718

Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevE.88.032718/fulltext