Chorusing is commonly considered a coordinated acoustic behaviour by two or more individuals so that their unison vocalizations overlap with a high degree of temporal precision (Voigt et al 2006). Different evolutionary functions has been advanced, including reproduction and social facilitation in the form of anti-predatory response or cooperative aspect (Brook et al 2000). An increase in acoustic activity with overlapped sounds was proposed by Norris et al. (1994) and Lammers (2004) for spinner dolphins, with the function to alert all members of the group’s intentions and readiness of the “acoustic community” for a hunt. Here we report the use of chorusing in a population of Atlantic spotted dolphins around the Eastern Islands of the Canary archipelago. We recorded 55 sightings, consisting in 9.56 hours of acoustic and behavioural data, with a towed array composed by 2 medium- and 2 high-frequency hydrophones. Observations were attributed to the following contexts: 19 travelling (mean duration=0.18 hours (sd=0.13), 13 feeding (0.27 (sd=0.21), 9 milling (0.08 (sd=0.05), 7 socializing (0.18 (sd=0.12), and 7 resting (0.13 (sd=0.09). Chorusing activity was present only during feeding in 3 sightings recorded during daylight hours. Stereotyped sequences of overlapped whistles were composed by groups of vocalizations separated by a silence period of 0.5-1.5 seconds. We performed a randomization test in order to assess if the probability of observing a sequence of 2 repetitions during feeding was higher than chance (P < 0.001). Repetition rate (number of repetition/duration of the sighting) was not correlated with the group size and with the weather conditions. The coordination of this acoustic behaviour supports the hypothesis of a social facilitation function in cooperation among individuals of a species, already known to forage in coordinated movements (Fertl et al 1995). A comparison with congenerics could assess if this acoustic behaviour is peculiar of the species.
Chorusing underwater: Atlantic spotted dolphin’s acoustic activity during feeding
PAPALE, ELENA;GIACOMA, Cristina;
2013-01-01
Abstract
Chorusing is commonly considered a coordinated acoustic behaviour by two or more individuals so that their unison vocalizations overlap with a high degree of temporal precision (Voigt et al 2006). Different evolutionary functions has been advanced, including reproduction and social facilitation in the form of anti-predatory response or cooperative aspect (Brook et al 2000). An increase in acoustic activity with overlapped sounds was proposed by Norris et al. (1994) and Lammers (2004) for spinner dolphins, with the function to alert all members of the group’s intentions and readiness of the “acoustic community” for a hunt. Here we report the use of chorusing in a population of Atlantic spotted dolphins around the Eastern Islands of the Canary archipelago. We recorded 55 sightings, consisting in 9.56 hours of acoustic and behavioural data, with a towed array composed by 2 medium- and 2 high-frequency hydrophones. Observations were attributed to the following contexts: 19 travelling (mean duration=0.18 hours (sd=0.13), 13 feeding (0.27 (sd=0.21), 9 milling (0.08 (sd=0.05), 7 socializing (0.18 (sd=0.12), and 7 resting (0.13 (sd=0.09). Chorusing activity was present only during feeding in 3 sightings recorded during daylight hours. Stereotyped sequences of overlapped whistles were composed by groups of vocalizations separated by a silence period of 0.5-1.5 seconds. We performed a randomization test in order to assess if the probability of observing a sequence of 2 repetitions during feeding was higher than chance (P < 0.001). Repetition rate (number of repetition/duration of the sighting) was not correlated with the group size and with the weather conditions. The coordination of this acoustic behaviour supports the hypothesis of a social facilitation function in cooperation among individuals of a species, already known to forage in coordinated movements (Fertl et al 1995). A comparison with congenerics could assess if this acoustic behaviour is peculiar of the species.
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