Infanticide by males is a phenomenon common in species in which the reproductive output of large numbers of females can be monopolized by a small number of males. It is thought to increase a male’s fitness, at the expense of the fitness of the infant’s parents, by bringing females into season more quickly. Infanticide by males has been recorded in just three cetacean species. We report aggressive behavior suggestive of infanticide in a fourth, the Amazon river dolphin (Inia geoffrensis). We observed and photographed a series of attacks on a neonate Amazon river dolphin by a large male, with apparent protective behavior by the mother. Although infanticide was not confirmed, the forceful, aggressive behaviors were highly suggestive of infanticidal behavior and represent another important data point for comparative studies of infanticide in mammals. Amazon river dolphins may have a polygynous, polyandrous, or promiscuous mating system, the latter two of which are not the norm in species in which the reproductive output of large numbers of females are monopolized by a small number of males. However, sexual dimorphism, high rates of aggression by males, socio-sexual object-carrying displays by males, and a long interbirth interval suggest that successful male Amazon river dolphins may be able to monopolize a large proportion of mating opportunities, and it is plausible that male dolphins can improve their reproductive success by bringing females into estrous sooner by killing the offspring of other males.
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We thank Pam Bucur and the staff of Amazon Explorama Lodges for their assistance with logistics during our observations. We thank the editors and two anonymous reviewers for their detailed and helpful comments on our manuscript.
Compliance with ethical standards
All applicable international, national, and institutional guidelines for the care and use of animals were followed.
Conflict of interest
The authors declare that they have no conflict of interest.
Best, R. C. & Da Silva, V. M. 1993. Inia geoffrensis. Mamm Species, 1–8Google Scholar
Bruno S, Politi E, Bearzi G (2004) Social organisation of a common dolphin community in the eastern Ionian Sea: evidence of a fluid fission-fusion society. Eur Res Cetac 15:49–51Google Scholar
Díaz López B, López A, Methion S, Covelo P (2017) Infanticide attacks and associated epimeletic behaviour in free-ranging common bottlenose dolphins (Tursiops truncatus). J Mar Biol Assoc U K:1–9Google Scholar
Dunn DG, Barco SG, Pabst DA, Mclellan WA (2002) Evidence for infanticide in bottlenose dolphins of the Western North Atlantic. J Wildl Dis 38:505–510CrossRefPubMedGoogle Scholar
Gomez-Salazar C, Trujillo F, Whitehead H (2012) Ecological factors influencing group sizes of river dolphins (Inia geoffrensis and Sotalia fluviatilis). Mar Mamm Sci 28:E124–E142CrossRefGoogle Scholar
Hrdy SB (1979) Infanticide among animals: a review, classification, and examination of the implications for the reproductive strategies of females. Ethol Sociobiol 1:13–40CrossRefGoogle Scholar
Kaplan J, Lentell BJ, Lange W (2009) Possible evidence for infanticide among bottlenose dolphins (Tursiops truncatus) off St. Augustine, Florida. Mar Mamm Sci 25:970–975CrossRefGoogle Scholar
Karczmarski L (1999) Group dynamics of humpback dolphins (Sousa chinensis) in the Algoa Bay region, South Africa. J Zool 249:283–293CrossRefGoogle Scholar
Lunardi DG, Ferreira RG (2014) Fission-fusion dynamics of Guiana dolphin (Sotalia guianensis) groups at Pipa Bay, Rio Grande do Norte, Brazil. Mar Mamm Sci 30:1401–1416CrossRefGoogle Scholar
Mann J, Connor RC, Barre LM, Heithaus MR (2000a) Female reproductive success in bottlenose dolphins (Tursiops sp.): life history, habitat, provisioning, and group-size effects. Behav Ecol 11:210–219CrossRefGoogle Scholar
Mann, J., Connor, R. C., Tyack, P. & Whitehead, H. 2000b. The bottlenose dolphin: social relationships in a fission–fusion Q10 society. Cetac Soc: Field Stud Dolphins and Whales, 91–126Google Scholar
Mann J, Smuts B (1999) Behavioral development in wild bottlenose dolphin newborns (Tursiops sp.). Behaviour 136:529–566CrossRefGoogle Scholar
Martin A, Da Silva V (2004) River dolphins and flooded forest: seasonal habitat use and sexual segregation of botos (Inia geoffrensis) in an extreme cetacean environment. J Zool 263:295–305CrossRefGoogle Scholar
Martin A, Da Silva V (2006) Sexual dimorphism and body scarring in the boto (Amazon river dolphin) Inia geoffrensis. Mar Mamm Sci 22:25–33CrossRefGoogle Scholar
Mcguire TL, Aliaga-Rossel ER (2007) Seasonality of reproduction in Amazon River dolphins (Inia geoffrensis) in three major river basins of South America. Biotropica 39:129–135CrossRefGoogle Scholar
Mintzer VJ, Lorenzen K, Frazer TK, Silva VM, Martin AR (2016) Seasonal movements of river dolphins (Inia geoffrensis) in a protected Amazonian floodplain. Mar Mamm Sci 32:664–681CrossRefGoogle Scholar
Nery MF, Simao SM (2009) Sexual coercion and aggression towards a newborn calf of marine tucuxi dolphins (Sotalia guianensis). Mar Mamm Sci 25:450–454CrossRefGoogle Scholar
Norris, K. S., Wursig, B., Wells, R. S. & Wursig, M. 1994. The Hawaiian spinner dolphin, Univ of California PressGoogle Scholar
Parra GJ, Corkeron PJ, Arnold P (2011) Grouping and fission–fusion dynamics in Australian snubfin and Indo-Pacific humpback dolphins. Anim Behav 82:1423–1433CrossRefGoogle Scholar
Patterson I, Reid R, Wilson B, Grellier K, Ross H, Thompson P (1998) Evidence for infanticide in bottlenose dolphins: an explanation for violent interactions with harbour porpoises? Proc Royal Soc London B: Biol Sci 265:1167–1170CrossRefGoogle Scholar
Pearson HC (2009) Influences on dusky dolphin (Lagenorhynchus obscurus) fission-fusion dynamics in Admiralty Bay, New Zealand. Behav Ecol Sociobiol 63:1437–1446CrossRefGoogle Scholar
Perrtree RM, Sayigh LS, Williford A, Bocconcelli A, Curran MC, Cox TM (2016) First observed wild birth and acoustic record of a possible infanticide attempt on a common bottlenose dolphin (Tursiops truncatus). Mar Mamm Sci 32:376–385CrossRefGoogle Scholar
Shirihai, H., Jarrett, B. & Kirwan, G. M. 2006. Whales, dolphins, and other marine mammals of the world, Princeton University PressGoogle Scholar
Slooten E (1994) Behavior of Hector’s dolphin: classifying behavior by sequence analysis. J Mammal 75:956–964CrossRefGoogle Scholar
Van Schaik, C. P., Pradhan, G. R. & Van Noordwijk, M. A. 2004. Mating conflict in primates: infanticide, sexual harassment and female sexuality. Sexual selection in primates: new and comparative perspectives. Cambridge University Press, Cambridge, 131–150Google Scholar
Zheng R, Karczmarski L, Lin W, Chan SC, Chang W-L, WU Y (2016) Infanticide in the Indo-Pacific humpback dolphin (Sousa chinensis). J Ethol 34:299–307CrossRefGoogle Scholar