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

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Smart tag helps conservationists understand penguin feeding strategies

Penguins provide for their young in constantly changing and difficult conditions. To help conservation efforts, SOUNDBITES developed a multisensor tag to investigate how penguins develop and adapt foraging habits.

Fundamental Research

Penguin colonies face multiple challenges including climate change, fishing and pollution. In the case of Antarctic Adélie penguins, it is known that chick survival depends greatly on the availability and accessibility of prey. In 2017, only two chicks from Petrel Island survived, from a colony of over 18 000 breeding pairs. It is thought that climate change is to blame as it prolongs sea ice, reducing food supplies. However, the region’s inaccessibility makes corroborative fieldwork difficult, so the Marie Skłodowska-Curie Actions supported SOUNDBITES project in the development of equipment for monitoring and analysing penguin foraging behaviour. “Our multisensor tag enabled us to identify call exchanges throughout foraging trips, suggesting that locating prey is partly a social effort,” explains Marie Skłodowska-Curie fellow, Danuta Wisniewska. “We are now cataloguing the recorded repertoire to create a library of penguin calls.” The recordings provide the first data on the acoustic environment of wild Adélie penguins.

On the penguin trail

SOUNDBITES developed a digital tag (DTAG) based on an earlier version. This seabird DTAG data logger consisted of a GPS, underwater microphones called hydrophones, pressure and temperature sensors, accelerometers and magnetometers, and a microprocessor to control the sensors and store the data. An algorithmic detector was also developed to analyse the data and identify instances of penguin feeding. The team first confirmed, using high-speed cameras and captive penguins at Nagoya Public Aquarium, that prey capture correlated with a rapid change in penguin acceleration. While also confirming that the equipment could record this acceleration, it was learned that acceleration had to be sampled at least 100 Hz. The system was then tested with Antarctic Adélie penguins to verify the detector’s efficacy and investigate penguin foraging behaviour. Eight penguins were equipped with small cameras attached to their upper backs which recorded for 4.5 to 6 hours. To reduce the load, rather than attaching the full DTAG, a small data logger was also fitted to their lower backs, including a small high-speed (100 Hz) accelerometer, alongside depth and GPS sensors. Four penguins provided several hours of good foraging video which was evaluated for visible feeding and surfacing events and then compared with the acceleration data on the logger. “Our accelerometers successfully recorded high-frequency acceleration signatures from rapid head and beak movements, characteristic of feeding. This enabled our detector to correctly identify most feeding events,” notes Wisniewska. To investigate social interaction, six breeding pairs were fitted with data loggers which recorded for up to 6 days, during foraging trips. Additionally, 11 penguins were fitted with the DTAGs to map and assess the context of any calls and vocal interchanges with other penguins at sea. The team wanted to know the degree to which birds used spatial memory and information from previous trips to locate prey, and whether they shared that information. “The loggers recorded sound and vibrations associated with vocalisation by the tagged individual, as well as sounds from other penguins nearby, indicating vocal exchanges. This suggests a social component to foraging,” adds Wisniewska.

‘Bellweather’ birds

As Adélie penguins are ‘bellweathers’ of the sea-ice ecosystem, SOUNDBITES insights contribute to the monitoring of this vital ecosystem. A paper is currently under way and all the GPS tracks recorded will be uploaded to Movebank, hosted by the Max Planck Institute for Ornithology. The data will also be shared with the Scientific Committee on Antarctic Research via the SCAR Antarctic Biodiversity Portal and the analytical workflows archived on GitHub.

Keywords

SOUNDBITES, penguin, Antarctic, foraging, sensors, tag, food, climate change, hydrophone, accelerometer

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