Abstract
Infanticide has been observed in several mammalian taxa and studied in considerable detail in carnivores and primates. Although reported previously in cetaceans, known cases are few and their socio-behavioral context remains poorly understood. We report here on three cases of social coercion directed at mother-neonate pairs of Indo-Pacific humpback dolphins (Sousa chinensis) in the Pearl River Estuary, southeast China. Two of these cases resulted in confirmed infanticide. To aid the interpretation of our field observations, we refer to the results of necropsies of calf carcasses stranded and recovered in our research area between 2003 and 2012, which indicate that in several cases the main cause of death of stranded calves was asphyxia resulting from blunt-force trauma. This is consistent with the aggressive behaviors seen during our field observations. We conclude that male infanticide is the most plausible interpretation of the observed behaviors, never previously reported for the genus Sousa, while the calf-directed aggression is likely a result of socio-sexual harassment by males as part of their reproductive strategy.
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Acknowledgments
This work is part of a larger-scale study supported by funding from the Research Grants Council of Hong Kong (GRF grants HKU768110M, HKU768913M and HKU17100015M), the National Natural Science Foundation of China (Grant Nos. 41276147 and 41576128), the Ocean Park Conservation Foundation Hong Kong and the Sousa chinensis Conservation Action Project of the Administration of Ocean and Fisheries of Guangdong Province, China. We thank Yuen-Wa Ho, Scott Y. S. Chui, Shiang-Lin Huang and Carmen K. M. Or for comments on an earlier draft of the manuscript, and Yingku Wang, Wenhua Liu, and laboratory staff at Sun Yat-sen University for their contribution to postmortem analyses.
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R. Zheng and L. Karczmarski contributed equally to this work.
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10164_2016_475_MOESM1_ESM.jpg
Supplementary material S1. Photo-ID images indicating the age of all individuals involved in the three cases of calf-directed aggression in Indo-Pacific humpback dolphins seen in the Pearl River Estuary in 2011 and 2012. In this species, the pattern of pigmentation changes with age, from dark gray at birth to light gray as juveniles and mottled or light pink as adults (for details see Jefferson 2000, Jefferson et al. 2012). White ID numbers on black background indicate the presumed mothers and black ID numbers on white background depict the perpetrators. One of the perpetrators was a large sub-adult and all other individuals were adults (JPEG 3993 kb)
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Zheng, R., Karczmarski, L., Lin, W. et al. Infanticide in the Indo-Pacific humpback dolphin (Sousa chinensis). J Ethol 34, 299–307 (2016). https://doi.org/10.1007/s10164-016-0475-7
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DOI: https://doi.org/10.1007/s10164-016-0475-7