Dusky dolphin (Lagenorhynchus obscurus) social structure characterized by social fluidity and preferred companions

Abstract

Many coastal delphinids exhibit social structures with a high degree of fission‐fusion dynamics. However, little is known about fission‐fusion dynamics in semipelagic delphinids such as dusky dolphins (Lagenorhynchus obscurus). We analyzed dusky dolphin social structure in a winter foraging habitat in New Zealand. We examined the population‐level societal attributes of preferred/avoided companions, behaviorally specific preferred/avoided companions, and simple ratio (SR) association index strength and distribution and the dyad‐level societal attribute of temporal patterning of associations. We identified 741 individuals; 99 met inclusion criteria for analysis. Long‐term and short‐term preferred/avoided companions were present in the pooled (6 yr) and annual samples. Individuals were observed to form long‐term but not short‐term preferred/avoided companions during all behavioral states. Mean and maximum SRs were 0.03 ± 0.01 SD and 0.40 ± 0.20 SD, respectively. Temporal analysis indicated that individuals associated preferentially throughout the study period. Dusky dolphins exhibited high social fluidity, as indicated by many weak and few strong associations. However, there was stability as individuals were observed to form behaviorally specific preferred/avoided companions and associate preferentially throughout the 6 yr period. Dusky dolphins thus display a dynamic social structure where overall low levels of bonding are juxtaposed against a subset of the population that forms strong bonds.

Bottlenose dolphin (Tursiops truncatus) social structure in the Shannon Estuary, Ireland, is distinguished by age‐ and area‐related associations

“…The final identifications of each individual dolphin in each sighting were verified by the lead researcher, who had the most photo‐id experience, as recommended by Pearson et al . (). The long‐term monitoring of this relatively small population, coupled with the high encounter rate, knowledge of life history, and well‐maintained photo‐id catalog of 204 known individuals (recorded between 2008 and 2016) greatly enhanced the process and efficiency of individual dolphin identification.…”

Dusky dolphin group dynamics and association patterns in Península Valdés, Argentina

“…In Admiralty Bay a similar pattern was observed, but in addition to this social fluidity, Pearson et al . () found that some individuals were observed to form long term bonds throughout the entire study period. In our study, constant companions were not the preferred model; nevertheless Würsig and Bastida () reported that two dusky dolphins that were tagged together in the Península Valdés area in the 1970s were recaptured 780 km to the north seven years later.…”

“…In Admiralty Bay, New Zealand, dusky dolphins were observed to form preferred/avoided long‐term companions during all behavioral states (Pearson et al . ). Pearson () found that during foraging, the frequency of preferred associates was higher and the frequency of acquaintances was lower, indicating that foraging associates may “know” each other well.…”

“…However, within this fluid society, some individuals associate preferentially during certain behaviors (foraging and socializing) and maintain relatively long‐term bonds (Pearson et al . ). Pearson () suggested that differences in association patterns between Kaikoura and Admiralty Bay might be related to differences in predation pressure and prey availability.…”

“…, Pearson et al . ), and they arrange themselves in a fluid society with a high degree of “social mixing” (Pearson ). However, within this fluid society, some individuals associate preferentially during certain behaviors (foraging and socializing) and maintain relatively long‐term bonds (Pearson et al .…”