PERTH - Much like a suitor woos his object of desire with a bouquet of roses, dolphins do so with sponges.

Researchers have captured this rare behaviour: male humpback dolphins presenting females with large marine sponges in an apparent effort to mate.

The researchers had observed a male dolphin dive below the ocean's surface and remove a marine sponge that was stuck on the seafloor. Steadily balancing it on its beak, the dolphin then presented the sponge it to its potential lover.

After a decade's worth of research on these Australian humpback dolphins, the scientists from the University of Western Australia's (UWA) School of Biological Sciences, the University of Zurich and Australia's Murdoch University discovered that this was a regular occurrence.

Said lead author Simon Allen, who is from UWA's School of Biological Sciences: "We were at first perplexed to witness these intriguing behavioural displays, but as we undertook successive field trips over the years, the evidence mounted."

It is rare to see sexual displays from mammal animals, said UWA in a statement.

"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," he added.

Dolphins are known to be extremely intelligent, and possess many human traits. They have distinct personalities, a strong sense of the self, love to play and can think about the future. They can also pick up new behaviour from one another. Bottlenose dolphins, for instance, can recognise themselves in a mirror and use it to inspect various parts of their bodies.

The scientists suggested that the latest example of sponges as gifts could be the male dolphins showing off in order to present their strength - making them irresistible mating partners.

Aside from the sponge gift to entice females, the male dolphins were also found to be performing visual and acoustic displays. Some larger males were working in pairs to deliver their gifts, which is extremely uncommon as mating success cannot be shared.

This new discovery has paved the way for more research into whether delivering these sponge gifts to female humpback dolphins can improve the male's chance of mating, the researchers said.

Romance in the animal kingdom

Romance is certainly not dead in the animal kingdom, and dolphins aren't the only animals going all out to entice mating partners with a labour of love. Here are some examples of animals which use gifts to impress their ladies.

Gentoo Penguins

Male Gentoo penguins, commonly found on the Antarctic peninsula, present love tokens in the form of pebbles to females. The penguins strive to find the smoothest looking pebbles and have often been caught stealing pebbles from their male rivals, to win the hearts of their female counterparts' hearts.

Puffer Fish

Puffer fish are another group in the water that believe in romance. The male fish, small as they are, swim through the ocean bed to create large and intricate "crop circles", which are intricate geometric sand sculptures the males make by laboriously using their fins to dig furrows. The circles are a way to attract female puffer fish to mate. Here, a male (right) is seen gently biting on the left cheek of a female while the couple are spawning.

Bowerbirds

Bowerbird males are known to pull out all the stops to attract females. The birds, native to New Guinea and Australia, create colour-coordinated nest-like structures to attract females from afar. They build an entire structure using items, ranging from bones and flowers to pens and clothes pegs, always in a specific colour scheme.