QUANTIFYING THE RATE OF FISSION-FUSION A Shark Bay Bottlenose Dolphin Study
One of the most notable and rare features in animal societies is a high degree of fission-fusion (FF) in which individuals change group membership frequently. This temporal-spatial fluidity is presumed to confer reproductive or survival benefits, allowing individuals to exploit their environment and decrease intraspecific competition. Bottlenose dolphins exhibit this trait to an extreme, arguably more so than humans. Similar to the society at large, dolphin mothers and calves separate and reunite often, possibly helping calves negotiate their social networks in a range of contexts. This study on mother-calf pairs in Shark Bay, Australia, is one of the first to quantify the FF rate (changes in group composition per hour). For calves (N=56), the FF rate was 10.34.56 times per hour (meanSE). Male and female calves changed group membership at similar rates (Male: 10.54.48 times per hour; N = 25; Female: 10.34.53; N = 29). We also examined this pattern developmentally, from birth to weaning. The FF rate in the first year of life was significantly greater than each subsequent year. We suggest that the early years are critical for learning to navigate a complex social and physical environment, e.g., locate resources and associates, avoid permanent mother-calf separations, predation and aggressive conspecifics. The maternal fission-fusion rate was lower than the calf rate at 4.742.54 (N = 65). We also examined the relationship between birth order and sex of the offspring, and maternal fission-fusion rate to help explain variation across pairs. Maternal rate was the only significant predictor iii of the calf rate, consistent with the prediction of the Maternal Influence Hypothesis. However, maternal style may contribute to substantial variation in the mean rates among birth order of the calves, and the sample sizes are too small to reject the null. Future research should examine directionality (who joins-leaves whom), other age-sex classes, and how FF rates relate to group size, behavioral context, and other demographic and ecological factors.
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Dispersal in bottlenose dolphins : bisexual locational philopatry, male-biased mother-offspring disassociation, and the role of fission-fusion dynamics Tsai, Yi-Jiun Jean. (Georgetown University, 2010)
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