Sound it out: inferring foraging ecology from a predator-embarked acoustic recorder

Periodic Reporting for period 1 - SOUNDBITES (Sound it out: inferring foraging ecology from a predator-embarked acoustic recorder)

Berichtszeitraum: 2018-05-14 bis 2020-05-13

Like many seabirds, penguins face the challenge of provisioning young on shore from a constantly changing food resource at sea requiring efficient localization and exploitation of ephemeral prey aggregations. For penguins, this critical activity is taking place against a backdrop of global warming which is rapidly changing the physical and biological environment in the Southern Ocean. Given the difficulties and expense in following animals at sea, bio-logging, i.e. animal-attached data recording devices have been a key tool for studying penguins and have yielded important data on individual movement and foraging tactics. However, for an animal that is so notably social in its dense colonies, remarkably little is known about social interactions at sea or within the colony, and whether these aid or thwart foraging. SOUNDBITES aimed to collect the first acoustic and multi-sensor data from penguins during foraging trips to gain new insights into how penguins locate and exploit resources. Our specific objectives were to (I) develop and test on captive seabirds a multi-sensor acoustic data logger, the seabirdDTAG, that would enable studies of penguin interactions, foraging ecology and energetics, (II) deploy the tag on free-ranging Adélie penguins in the Antarctic, to examine the role of intraspecific communication in resource acquisition through studies of foraging decisions during consecutive foraging trips in breeding partners.

SOUNDBITES took advantage of state-of-the-art miniature electronic devices for logging sound, movement and position of animals that were originally developed for marine mammals, and within SOUNDBITES, modified for use on penguins. The dynamic range of the device’s sensors and its sampling protocols were chosen so as to accurately record penguin behaviour, and were therefore based on earlier data on Adélie penguins collected by SOUNDBITES’ host laboratory. Accordingly, the seabirdDTAG (67 x 30 x 21 mm, 60 g in air) can record acoustic data at an adjustable sampling rate of up to 192 kHz, and high-resolution depth and 3-D orientation of the tagged bird by means of a pressure sensor and tri-axial accelerometers and magnetometers sampled at 50 Hz and up to 1000 Hz (adjustable), respectively. The data logger also includes a fast-sampling GPS, which provides high-accuracy tracking of animals that surface irregularly and for short intervals. The logger’s recording time depends on its sampling settings, but during SOUNDBITES, its rechargeable battery allowed up to 6 days of continuous data collection. To ensure the seabirdDTAG’s applicability in studies of acoustic communication, foraging ecology and energetics of penguins, during SOUNDBITES, we tested the logger’s ability to record sound in air and in water, and provide reliable estimates of timing of foraging events through recordings of captive chinstrap, Adélie and gentoo penguins hosted by Nagoya Public Aquarium, Japan. We developed an acceleration-based feeding detection algorithm that we tested by recording prey captures by the equipped captive penguins with tag-synchronised high-speed cameras. We confirmed that prey capture correlated with a rapid change in penguin acceleration that could be detected by a logger attached to the penguin’s lower back, but that required an acceleration sampling rate of at least 100 Hz to be reliably recorded. We then evaluated the performance of the feeding detection algorithm under natural conditions by equipping eight free-ranging Adélie penguins in the Antarctic with a lower-back-mounted multi-sensor logger and an upper-back-mounted camera logger to simultaneously record acceleration and prey captures. Four of the eight penguins provided good video data with several hours of foraging. The timing of all feeding events visible in the videos was compared with the output of our feeding detection algorithm. Our detector correctly identified between 72 and 88% of feeding events, with a false alarm rate of about 10%. It missed between 12 and 16% of feeding events. These results and the feeding algorithm will be presented at the 7th International Bio-logging Science Symposium (postponed to September 2021 due to the COVID-19 pandemic) and in a peer-reviewed journal article (submitted by the end of January 2021). To investigate the role of social interactions in resource acquisition, during SOUNDBITES, we instrumented a total of 23 wild Adélie penguins in the Antarctic (17 with seabirdDTAG and 6 with a smaller non-acoustic multi-sensor data logger, including 6 breeding pairs with both partners instrumented, and 14 birds instrumented during consecutive foraging trips) during the chick-guard stage of the breeding season (i.e. when both parents alternate foraging at sea and chick attendance at the nest for 2-4 days at a time; mid-December to mid-January). We found that the seabirdDTAG’s high-speed accelerometers can record vibrations associated with vocalization by a tagged penguin, allowing us to distinguish communication calls made by the tagged individual from those produced by other individuals nearby. This in turn allowed us to show that penguins engage in vocal exchanges with conspecifics throughout their foraging trips at sea and prompted us to investigate whether and how social interactions at sea facilitate locating foraging patches. To that end, we are currently working on cataloguing the repertoire of calls recorded by the seabirdDTAG to create a library of vocalizations used by the penguins at sea and in the colony, as well as on mapping and assessing the context of any calls and vocal interchanges with conspecifics recorded by the logger. The results of this analysis will be submitted for publication in a peer-reviewed journal by spring 2021. Analysis is also ongoing on whether Adélie penguins return to high-pay-off prey patches during consecutive foraging trips, and whether they might share information on location of such patches with their partners, however, most likely, further data collection will be required to fully address these questions.

The SOUNDBITES data are directly relevant to European Commission’s Biodiversity Strategy. They will help assess the resilience of these central place foragers to changing environment and resources and, by aiding the interpretation of movement data already collected from penguins, increase the value of an important decade-scale monitoring effort. The foraging behaviour and breeding success of Adélie penguins are closely related to sea-ice conditions and dynamics. Integrating changes occurring at lower levels in the trophic network, Adélie penguins are often referred to as the ‘bellwether’ of the sea-ice ecosystem. By enabling efficient tracking and mapping of foraging rates of these birds over time and providing insights into the drivers of their foraging decisions, SOUNDBITES will, contribute to the monitoring of this vital ecosystem, and link to at least two of the UN Sustainable Development Goals: : #13 Climate Action and #14 Life Below Water. Furthermore, the recordings made during the field part of SOUNDBITES, provide the first data on the acoustic environment experienced by free-ranging penguins, invaluable as baseline for evaluation and for optimization of future on-animal ambient noise recordings.

Danuta Wiesniewska SOUNDBITES

Periodic Reporting for period 1 - SOUNDBITES (Sound it out: inferring foraging ecology from a predator-embarked acoustic recorder)

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