Interspecies pectoral fin contact between bottlenose dolphins and Atlantic spotted dolphins off Bimini, The Bahamas

Agonistic interactions initiated by adult bottlenose dolphins on Antillean manatee calves in the Caribbean Sea

The dynamics and drivers of inter-species interactions in the wild are poorly understood, particularly those involving social animal species. Inter-species interactions between cetaceans and sirenians have rarely been documented and investigated. Here, we report 10 cases of interaction initiated by adult bottlenose dolphins (Tursiops truncatus) towards Antillean manatee (Trichechus manatus manatus). Interactions were documented through behavioral observations in the wild (n = 7) and from the examination of orphaned calves (i.e., tooth rake marks on their body; n = 4) that entered a rehabilitation facility, one individual both observed interacting with dolphins and found stranded with bite marks. Bottlenose dolphins were observed interacting with orphan manatee calves and with mother-calf pairs, exhibiting agonistic behavior (n = 2), affiliative or neutral behaviors (n = 1), but the behavioral contexts of these interactions remain unclear in most cases (n = 7). Information on stranded individuals was collected from four calves (of 13 examined calves) recovered in poor condition with bottlenose dolphin tooth rakes and bite wounds on their bodies, one of which died. Injury from bite wounds varied in extent and severity, ranging from superficial scratches leaving rake marks to deep lacerations. Our findings suggest the regular occurrence of agonistic behaviors initiated by adult bottlenose dolphins and directed toward manatee calves. However, the drivers of these interactions remain unknown and need to be further investigated.

The partial merger of two dolphin societies

Interactions between mammalian social groups are generally antagonistic as individuals in groups cooperate to defend resources from non-members. Members of the family Delphinidae inhabit a three-dimensional habitat where resource defence is usually impractical. Here, we describe a long-term partial fusion of two communities of Atlantic spotted dolphins (Stenella frontalis). The northern community, studied for 30 years, immigrated 160 km to the range of the southern community, observed for 20 years. Both communities featured fission-fusion grouping patterns, strongest associations between adult males, and frequent affiliative contact between individuals. For the 5-year period following the immigration, we found members of all age classes and both sexes in mixed groups, but there was a strong bias toward finding immigrant males in mixed groups. Some association levels between males, and males and females, from different communities were as high as the highest within-community associations. Affiliative contacts indicate that these individuals were forming social relationships. The mixing of two separate social groups with new bond formation is rare in terrestrial mammal groups. Such mixing between spotted dolphin groups suggests that adaptations to respond aggressively to 'outsiders' are diminished in this species and possibly other ecologically similar dolphins.

Testing use of the first multi-partner cognitive enrichment devices by a group of male bottlenose dolphins

Alliance formation plays a crucial part in male dolphins' lives. These partnerships may last for decades or even for a lifetime; thus, partner choice and the maintenance of these relationships are both considered key components of alliance formation. In our previous investigations, pairs of adult male dolphins showed a high success rate in cooperative manipulation of a cognitive enrichment device. Here, we introduced two novel cognitive enrichment devices to the group of five dolphins, facilitating simultaneous actions for not only pairs, but for three or even four dolphins. The devices were made of PVC tubes, fittings and caps equipped with rope handles, creating a three-way (T-shape) and a four-way (TT-shape) device. The devices were filled with fish and ice and were designed to be opened by simultaneous pull of the handles. Both devices were tested in 12 trials (each lasted for 15 min), separately. Only one of the caps could be opened, the others were affixed with the position of the openable cap counter-balanced over the trials. Although the dolphins received no training regarding the manipulation of the devices, they were successful in cooperatively opening the three-way devices in 10/12 of trials (70% by two and 30% by three dolphins) and the four-way devices also in 10/12 trials (50% by two, 40% by three and 10% by four dolphins). The dolphins interacted with the devices during the entire testing time, and this was mostly spent in cooperative play (77% and 56% of the test duration with the three-way and four-way device, respectively). The majority of the cooperative play was observed between one particular pair of dolphins that was temporarily associated with a third or sometimes even with a fourth dolphin. These findings demonstrate the first successful use of multi-partner cooperative enrichment devices, providing information on the social organization of a male dolphin group.

A new approach to the study of relationship quality in dolphins: Framework and preliminary results

Proximity and synchronous behaviours from surface observations have been used to measure association patterns within and between dolphin dyads. To facilitate an investigation of relationship quality in dolphins, we applied a method used for primates and ravens that examined three main components to describe relationships: value, security, and compatibility. Using pilot data from long-term research of two study populations for this preliminary assessment, these three components were extracted from PCA of eight behavioural variables with more than 80 % variance accounted for in both study groups. Only pair swim position differed between groups. Although value, security, and compatibility are abstract terms, each is based on behaviours identified as important in dolphin social life, at least for these two populations. Examining relationship quality in dolphins with a method used to illustrate dyadic differences for primates and ravens allows for a quantitative, comparative assessment of sociality across disparate taxa. Although these species are diverse in their anatomies and in their social habitats (e.g., aquatic, terrestrial, aerial), they may well share the basic societal building blocks in the factors affecting how relationships are formed. We discuss how an examination of these behavioural variables facilitates understanding relationship quality in dolphins, as well as how dolphin relationships fit into the context of social animals' society.