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Other scientists conducting long-term studies of species noticed something similar going on. In 1970, Randall Wells, a biologist with the Chicago Zoological Society, began following bottlenose dolphins in Sarasota Bay in Florida, getting to know them so well that eventually he could distinguish one from another simply by the appearance of its dorsal fin. Over time, he discovered that some unrelated male dolphins spend considerable amounts of time together in pairs. "Usually they're swimming side by side," says Wells. "The rest of the time we'll see [them] alone, but they'll be back together again within a few hours."
Across a span of 40 years, Wells has been able to piece together the long-term history of these friendships. Male dolphins form their first friendships when they're young, and a pair will stay on good terms for years. If a male's friend dies, he will swim alone for a few months, but eventually he'll befriend another male.
Unrelated females do things differently. They spend time together during their fertile years, but these bonds are fluid, with individuals moving from one group to another in the bay. Only when they're in their 50s and no longer reproducing do female dolphins develop enduring bonds, and those are with just one or two other female friends.
One day in 2008, for example, Wells and his colleagues noticed that a 58-year-old female he named Nicklo had swum into the sea-grass meadows next to the lab. Dolphins sometimes go there to hunt the schools of mullet that frequent the shallow waters. As the mullet try to escape, the dolphin whacks them with its powerful tail, delivering a blow so hard it can launch fish into the air. A good fish whacking can leave a mullet stunned so the dolphin can make an easy meal of it.
But that day Nicklo was not whacking fish on her own. She was on the hunt with an unrelated old female named Black Tip Double Dip. The pair of dolphins drove the mullet schools from different sides, each whacking fish into the air.
Wells had rarely seen two female dolphins fish whacking together, but he began to see Nicklo and Black Tip Double Dip doing it more and more often. Sometimes they'd be joined by another old female named Squiggy. So much teamwork, of course, could simply be the utilitarian business of cooperative hunting: if three dolphins work together, all three eat better. But Wells and his colleagues would find the trio not just fish whacking but also simply swimming in tight formation, apparently keeping one another company. It's not quite The Golden Girls, but it's not all that different either.
As evidence for the F word piled up, the question shifted from "Do animals make friends?" to "Why do they bother?" The most obvious answer is that friendships boost reproductive odds. If having friends somehow leads to having more babies, the friendliness trait gets passed on, becoming more common across the species. For male dolphins, the reproductive benefit may come from a friend's playing wingman. A single male may have a hard time driving off other males while mating, but two males working together may be able to do the job. Females lean on one another more after their babies are born. A group of dolphin moms will often form circles around their calves, perhaps protecting them from predators. "We call them playpens," Wells says.