The formation of alliances between adult males for the purposes of coercing females is uncommon.
Male dolphins present females with large marine sponges, and perform visual and acoustic displays, in order to mate, scientists have found for the first time.
Scientists including those from the University of Western Australia (UWA) conducted a decade of boat-based research on coastal dolphins across north-western Australia.
They documented adult male Australian humpback dolphins presenting large marine sponges to females, as well as performing visual and acoustic displays.
It is the first time the behaviour has been documented in this species.
Their first observation was between a male and female dolphin and her calf. The male dolphin dived down to remove a large marine sponge fixed to the seafloor, balanced it on his beak and pushed it towards the female.
The use of objects in sexual displays by non-human mammals is rare and the researchers believe it could be a display of the males strength and quality as a mating partner.
"We were at first perplexed to witness these intriguing behavioural displays by male humpback dolphins, but as we undertook successive field trips over the years, the evidence mounted," said Simon Allen from UWA.
"Here we have some of the most socially complex animals on the planet using sponges, not as a foraging tool, but as a gift, a display of his quality, or perhaps even as a threat in the behavioural contexts of socialising and mating," said Allen, lead author of the study published in the journal Scientific Reports.
Some large adult male dolphins also appeared to be working together in pairs, said Stephanie King from UWA.
"The formation of alliances between adult males for the purposes of coercing females is uncommon, since mating success cannot be shared," King said.
"This is a new finding for this species, and presents an exciting avenue for future research," King said.