Many gregarious species require complex patterns of communication for maintaining coordinated behaviors, articulated social structure and group cohesion. In mammal species, social complexity has been considered the driving force for the development of advanced acoustic communication systems. Striped dolphins are highly social, showing large group size with females maintaining strong bonds with kin. Here, we tested the hypothesis that more complex acoustic pattern plays a key role in social activity in the striped dolphins. The production rate of clicks, whistles and burst pulses, and the acoustic features of whistles have been related to the activity context (feeding, traveling, resting, and socializing). Furthermore, complex calls, consisting of a combination of frequency-modulated, and/or pulsed components were detected. Higher whistles and burst pulses production rates were recorded during socializing. Also, the social activity can be discriminated basing on the modulation of the whistle contour. Biphonic calls were especially recorded during social interaction events, suggesting that these phenomena can encode information about individual or group identity to conspecifics. Outcomes indicate the pivotal role of vocal complexity during social context and elicit further investigations of the communication system of small odontocetes from local to wider spatial scale.

The evaluation of acoustic temporal rhythms in wide-ranging cetaceans can reveal patterns in animal spatial presence and the occurrence of periodical phenomena. Here, we aimed at assessing the temporal patterns of dolphin’s acoustic presence in a shallow-water area in the Sicily Strait (Mediterranean Sea). Whistles were collected continuously for 14 months from an acoustic monitoring station installed aboard of an elastic seamark. Over a total of 6955 h of recording, 14,048 signals were identified using both automatic and visual methods. Three parameters were analyzed: hourly presence (HP), used as a proxy of the presence of dolphins in the area; detection rate (DR), indicating the acoustic activity rate of dolphins measured per hour in the entire dataset; and detection rate in presence of dolphins (DRD), indicating the acoustic activity rate of dolphins considering only the hours when whistles were recorded. The highest values of both HP and DR were reached during the night, and the Autumn and Winter months, suggesting an increase in the dolphin’s occurrence and a possible moving away and towards the monitoring station potentially following prey. DRD, instead, showed an almost uniform distribution throughout the day implying that when the animals are close to the monitoring station, the acoustic activity does not show any pattern. However, possible changes in the communication exchange along the seasons were suggested. This study complements other work on this subject, improving the knowledge of dolphins’ acoustic activity in the area.

Background: The Mediterranean subpopulation of fin whaleBalaenoptera physalus(Linnaeus, 1758) has recently been listed as Vulnerable by the IUCN Red List of threatened species. The species is also listed as species in need of strict protection under the Habitat Directive and is one of the indicators for the assessment of Good Environmental Status under the MSFD. Reference values on population abundance and trends are needed in order to set the threshold values and to assess the conservation status of the population.Methods: Yearly summer monitoring using ferries as platform of opportunity was performed since 2008 within the framework of the FLT Med Network. Data were collected along several fixed transects crossing the Western Mediterranean basin and the Adriatic and Ionian region. Species presence, expressed by density recorded along the sampled transects, was inspected for assessing interannual variability together with group size. Generalized Additive Models were used to describe density trends over a 11 years’ period (2008–2018). A spatial multi-scale approach was used to highlight intra-basin differences in species presence and distribution during the years.Results: Summer presence of fin whales in the western Mediterranean area showed a strong interannual variability, characterized by the alternance of rich and poor years. Small and large groups of fin whales were sighted only during rich years, confirming the favorable feeding condition influencing species presence. Trends highlighted by the GAM can be summarized as positive from 2008 to 2013, and slightly negative from 2014 to 2018. The sub-areas analysis showed a similar pattern, but with a more stable trend during the second period in the Pelagos Sanctuary sub-area, and a negative one in the other two sub-areas. Our findings further confirm the need for an integrated approach foreseeing both, large scale surveys and yearly monitoring at different spatial scales to correct and interpret the basin wide abundance estimates, and to correlate spatial and temporal trends with the ecological and anthropogenic drivers.

Signature whistles are stereotyped and individually distinctive acoustic signals used as individual recognition calls, for maintaining group cohesion and during stressful situations. Here, it’s proved the occurrence of stereotyped whistles and how it changes, by an isolated adult female of short-beaked common dolphin (Delphinus delphis) kept in rehabilitation. Twenty-three hours of continuous recordings were collected until the dolphin death for hepatitis. A total of 64 whistles were analyzed along the hours and only an ascending-descending frequency contour was detected. The number of whistles decreased during the rehab period. Whistles showed a mean peak frequency contour (PFC) of 9.45 ±1.09 kHz, a mean maximum frequency value of 12.0.4 ±1.65 kHz, a mean minimum frequency of 7.04 ±1.16 kHz, a mean duration of 0.75±0.27 seconds and a number of harmonics ranging from 1 to 3. The low variability of whistles parameters along the hours and the only whistle contour found in an isolated and stressed dolphin support the hypothesis of stereotyped whistles. It is the first evidence of the use of this signal by Delphinus delphis in Southwestern Atlantic Ocean (SWAO) and is first step to understand the sound production related to the rehabilitation process.