Social and reproductive behaviors

Abstract

Sirenian social and reproductive behaviors lack much complexity or diversity. Whereas sirenians are usually sighted as solitary, or as cows with single calves, aggregations of many individuals can occur. Persistent social groupings are unknown. Home ranges are widely overlapping. Mating systems of dugongs ( Dugong dugon ) have been variously described as leks or as scramble promiscuity (mating herds ) and lone mating pairs have been observed in areas of low density, but further research into the hypothesized leks is needed (especially because scramble promiscuity has been observed in the same region). Dugongs and all manatees ( Trichechus ) show scramble promiscuity, wherein males form groups that escort single females with much physical contact for many days. The strongest social bonds are between females and nursing calves. Florida manatees ( Trichechus manatus latirostris ) show natal philopatry for years after weaning. Socially transmitted knowledge (tradition) appears important to Florida manatees and perhaps all species of sirenians, particularly in regions where seasonal movements during winter are necessary for survival, such as in winter for Florida manatees, and dugongs at the high latitude limits of their range. Some populations of Antillean, Amazonian, and African manatees have regular movements in response to seasonal flooding and access to food, which also may be learned through tradition . Dugongs may rely on group movements based on traditional knowledge in response to regional loss of food supply from extreme weather events. Communication is most obvious through vocalizations, which can show individual distinctiveness. Vocal communication is most prevalent between mothers and calves. Allomaternal care occurs in Florida manatees at shared aggregation sites. Florida manatees occupying a given region can consist of multiple matrilines that develop through the early bonding of calves to mothers and subsequent natal philopatry. Population genetics research supports male-biased dispersal and possible female-based philopatry in other trichechids, but perhaps not as strongly in dugongids. Considerable further research is needed on these and related topics to more comprehensively understand sirenian social and reproductive behavior.