Have you ever noticed how best friends tend to talk like each other?

Whether it's chickadees or chimps, scientists have found that numerous species will tweak their calls to resemble those of their closest compatriots.

However, the exact opposite seems to be true for male bottlenose dolphins in Western Australia's Shark Bay, according to a study published June 7 in the journal Current Biology.

Decades of research in the region has shown unrelated males team up in groups of two to three. This improves their chances at finding and breeding with females, which live in their own family-based pods. Additionally, several of these male duos or trios will sometimes form larger, second-level alliances—some of which can last their lifetimes. (Read about new, intimate details of dolphin sex.)

Males each have their own signature whistle, sort of like a human name. And while a male might have the same “name” as another male outside of its pod, he never seems to share one with another male ally.

"These individual vocal labels, or 'names,’ allow the animals to develop complex social relationships,” says study leader Stephanie King, a research fellow at the University of Western Australia and a National Geographic Explorer.

These relationships are so tight, in fact, that the males spend a lot of time caressing each other with their pectoral fins. Drone footage has revealed they may even swim with their fins laying on top of each other, as if holding hands.

What’s in A Name?

Scientists have known that both male and female bottlenose dolphins have signature whistles somewhat akin to names since the 1960s.

But it wasn’t clear just how important the calls were until King started playing the whistles back to the animals themselves.

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Click here to read Male Dolphins Offer Likely Love Token to Females in Rare Video. Oct. 20, 2017 - Male humpback dolphins may use sea sponges in a surprising, yet romantic, way—to attract females. Marine biologists in Australia observed the males present, and even toss, sponges to prospective mates. The behavior was seen on 17 occasions in five separate dolphin pods. It's unknown how the females respond, and if the sponges even help the males in the quest for love.

In a 2013 study, King showed that dolphins respond to recordings of their own signature whistle, but not those of other dolphins—much like a student being called upon in a classroom.

She also learned that the dolphins can mimic each other’s whistles, seemingly to address or call out to one another.

King’s new study builds on these earlier discoveries by showing that the names seem to be crucial for building and maintaining an ever-evolving array of social bonds—something that likely wouldn’t be possible if every dolphin had the same name.

Because there can be up to 14 males in these second-level alliances, King says the dolphins must constantly keep track of various relationships.

“You need to know who are your friends, and who are your rivals, and who are the friends of your rivals,” she explains.

Body Language

The males further strengthen their bonds by both touching and practicing acts of striking synchrony, during which they swim in stride or surface to breathe at the same time—almost like a military unit marching in unison. (See 10 beautiful photos of dolphins.)

“Synchrony has also been linked to oxytocin release in humans, which promotes trust and cooperation,” says King.