On Isla Martillo in Tierra del Fuego, we continuously recorded in a colony of Magellanic penguins (Spheniscus magellanicus) in the beginning of the 2016 molting season. Here we describe the daily soundscape dynamics within this colony using existing soundscape metrics, which were developed to facilitate ecological inferences from multi-source soundscapes. While these indices have exhibited successes, little research has explored the utility of soundscape metrics for characterizing ecological patterns and processes when a single species dominates the soundscape. Bioacoustics offers tools for such applications, but soundscape metrics may be favorable in environments like penguin colonies where sounds of chorusing animals temporally overlap or when sounds are non-stereotypical. Some diel behavior patterns of Magellanic penguins have been previously documented by studies focusing on foraging behavior, but these studies relied on human observation and dive trackers mounted on individual birds. Instead, we consider the potential utility of terrestrial acoustic recording to monitor populations and behavior of this near-threatened species. We interpret our acoustic data in the context of known Magellanic penguin behavior and the few non-penguin sounds in this habitat, and through this interpretation we evaluate how soundscape metrics can be used to assess the populations and behavior of monospecific assemblages.
Two acoustic indices offered useful description of the temporal soundscape dynamics within the penguin colony. The acoustic diversity index (ADI) and the bioacoustic index (BAI) conveyed complementary information. The ADI showed fairly sharp peaks in acoustic activity around 05:00 – 06:00 and 20:00. Similarly, the BAI indicated a morning peak but more sustained evening activity. Penguins are likely on land and not sleeping at those times, meaning that changes in the onset and duration of those peaks might be useful for monitoring foraging and resting behavior. As few non-penguin sounds were heard on these recordings, these results indicate that certain acoustic indices designed to highlight aspects of community composition and dynamics can indeed be applied to nearly monospecific assemblages. We view these results favorably, as they suggest that acoustic monitoring without call detection may be feasibly implemented in monospecific colonies where long-term monitoring can offer powerful insights into behavior and population dynamics. While further work must associate these soundscape metrics with behavioral observations and population estimates, this application is highly promising, particularly for species of concern, such as the near-threatened Magellanic penguin.