Caroline E. Haas

Northern bottlenose whales ( Hyperoodon ampullatus ) are echolocating, deep-diving beaked whales found primarily in arctic and sub-arctic offshore waters. In the eastern North Atlantic, the species has been suggested to undergo seasonal north–south migrations, however, previous whaling data and more recent sighting surveys insufficiently covered the winter months. To address this data gap, bottom-moored hydrophone deployments (n = 8) were conducted at three locations in the Nordic Seas: off Jan Mayen (Norway; 2015–2017), north-east Iceland (2020–2022) and east Iceland (2020–2023). Automated click detection allowed identification of species-specific clicks. Detector precision and recall were manually evaluated using subsets of the data and precision was used to correct the weekly proportion of snapshots that contained clicks. Generalized additive mixed models were used to investigate whether environmental variables associated with prey availability explained occurrence patterns. Results revealed near year-round presence of northern bottlenose whales in the Nordic Seas with a gradual northward shift in spring between Iceland and Jan Mayen. The lowest numbers of detections occurred from July into September, contradicting the long-standing hypothesis of north–south migrations to enable overwintering at lower latitudes. The observed seasonal occurrence patterns were stable across years and associated with higher sea surface height variation, indicative of eddy activity. We interpreted this as support of a prey-driven distribution, as eddies characterize the spawning grounds of northern bottlenose whales’ main squid prey in the Nordic Seas, Gonatus fabricii . The observed occurrence patterns can inform planning of future anthropogenic activities in these waters to avoid habitat degradation and reduce stressors on this species.

Vocal individuality has important biological functions in mammals: at crucial stages of development, it ensures feeding and is a prerequisite for auditory-based mother–pup recognition. Is vocal individuality only shaped by maturation or also by the degree of conspecific acoustic input? Here, we test how the neonatal auditory environment shapes development and individualization of calls in harbour seal pups (Phoca vitulina). To simulate low- versus high-conspecific acoustic density, 18 pups heard playbacks of calls from either 2 or 30 conspecifics. We recorded calls before and after playback exposure and extracted 12 acoustic parameters. Supervised machine learning and discriminant function analyses showed greater individual distinctiveness in both groups after playback, indicating a developmental trend toward individualization. Notably, pups exposed to less-variable input showed higher individuality. Euclidean distances on call parameters showed that both groups diverged from the playback signals. Distances on within-pup and between-pups housed together revealed opposite trajectories in the two groups: after the exposure, less-variable auditory input determined steadier individual calls, while more-variable auditory input scattered calls across the acoustic space. Altogether, our findings indicate that auditory input modulates vocal development in pups, making harbour seals a promising model for unravelling how neonatal environment affects vocal plasticity in a non-human mammal. This article is part of the theme issue ‘Mechanisms of learning from social interaction’.

Basic knowledge about populations of short‐beaked common dolphins (Delphinus delphis) in the eastern part of the Mediterranean Sea is still lacking. Classified as ‘Endangered’ in an IUCN assessment released in 2022, it is necessary to gain baseline knowledge to understand the species’ population status and develop impactful conservation measures. The current study conducted boat surveys, employing visual and acoustic techniques between January 2019 and July 2022 in the Dilek Peninsula National Park, central Aegean Sea. Results revealed the continuous coastal presence of common dolphins, with subadults recorded during every sighting in low group sizes. Travelling‐related activities made up 58% of observed behaviour while resting comprised just 1%. Whistles were produced in the range of 1.83–48kHz with a peak frequency of 10.4kHz and median duration of 0.54s. Concave whistles were the most frequently recorded whistle type. Whistles were found to be generated when dolphins were interacting with boats and diving/travelling fast, forming 53% and 31% of whistle production respectively. The continuous presence of common dolphins, particularly subadults, emphasises the importance of the Dilek Peninsula. Whistle parameters show similarities with other common dolphin populations of the Mediterranean and Black Sea, albeit with shorter durations. The high whistle presence during boat interactions requires investigation to assess whether whistles carry avoidance or predatory messages, or whether there are potential consequences for the species’ energy budget. The current study presents preliminary information on the behavioural context of acoustic patterns. Further research is essential to understand the click and whistle characteristics within the biological, environmental and anthropogenic variables of their surroundings.