Adult mammals have the capacity to kill other members of their own species, but males and females generally seem to kill for different reasons.
Biologists have already studied mammalian infanticide, the killing of infants by adults of the same species, but the same isn’t true for killing adults. This means we don’t know as much about why adult mammals sometimes kill other adults within their species.
In order to figure out whether there are any patterns in killing behaviour, José María Gómez Reyes at the National Research Council Arid Zones Experimental Station in Spain and his colleagues analysed the causes of death among 1384 mammal species.
Of these, the team found evidence of adult killing in 352 species. It was particularly common among ungulates, primates and carnivores, but almost unheard of among bats, whales, dolphins and rabbits.
The team found that males were more likely to kill than females. Males were also more likely to target other males rather than females. What’s more, the male and female mammals generally had different motivations for killing adults of their species.
“It was interesting the relationship that we found between infanticide and female adulticide,” says Gómez Reyes.
While male mammals are more likely to kill other adult males to rid themselves of competition, female mammals kill more often to defend their young from attacking adults. However, females may also kill the young of other females when resources are scarce.
“Male contribution to reproduction is really light. They just produce sperm, and they mate as often as they can. So, to me it makes complete sense that the females are killing other adults in the context of protecting their young from infanticide,” says Kate Durrant at the University of Nottingham in the UK. “It’s protecting this investment that they’ve made, this heavy resource investment they’ve made in their offspring. They’re not gonna let them go without a fight.”
Journal reference: Proceedings of the Royal Society B: Biological Sciences, DOI: 10.1098/rspb.2021.1080
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