This article on bottlenose attacking and killing porpoises in really brutal ways is weird enough. But it also turns out that dolphins’ “crimes” against porpoises are kind of sexual in nature.
The killings coincide with the expansion of dolphin territory, but Cotter and Jefferson believe the primary motive is not territorial. The two species primarily feed on different things and do not generally frequent the same places at the same times, according to the porpicide study.
Jefferson said the killings appear to be sex-related.
“In some of the incidents recorded in the past, there has been activity focused on the genital area of the porpoise,” like bite marks or scraping, he said. “These bottlenose dolphins, we call them ‘porpitrators,’ were either known males or suspected males and mostly younger males.”
Cotter said the attacks do not appear to be sexual assaults as much as they are aggression caused by sexual frustration, much as one might find in a gang of teenage boys.
Male bottlenose dolphins are known to practice infanticide as a way of inducing estrous in females. It is possible, according to the study, that they are practicing their baby-killing techniques on porpoises, which are about the same size as young dolphins.
Cotter doesn’t believe that is the case.
“All the animals are subadults that are reaching sexual maturity, but they aren’t high ranking yet in the dolphin social structure and therefore don’t have access to females,” Cotter said. “All of these attacks seem to happen in the summer and into the fall, which coincides with the peak breeding time, so we lean toward sexual frustration not infanticide behavior.”
Wow. Any biologists out there care to elaborate what the hell is going on here?