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Flamingos are known for being an extremely social species. The flamboyant birds, sporting brilliant shades of pink, are almost always found in flocks in the wild. And during breeding season, they can gather by the hundreds and even thousands. Amid the crowds, groups will march around in huddles while performing synchronized moves like the “head flag,” when they stretch their necks and bills to the sky and rhythmically flip their heads. 

For years, though, zoo keepers and others who have spent time closely observing captive flamingo flocks have noticed that the birds might even be more social than we realize, with each flock comprising . These include not only the expected male-female mate pairs, but also strong bonds between same- and mixed-sex groups of two to four birds. Now, a recent published in Behavioral Processes shows evidence of friendships that persisted through five years of research focusing on American, Andean, Chilean, and Lesser Flamingo flocks, all of which were housed in open enclosures at the Slimbridge Wetland Centre in England. Paul Rose, a behavioral ecologist at the University of Exeter, who led this research, also found that several birds avoided flock members they didn’t get along with. “They have these really strong friendships and strong preferences for avoiding,” he says.

Rose, who studies nesting behavior in a Lesser Flamingo flock at the Slimbridge Centre, had grown accustomed to seeing some individuals together year after year. When he tried to look into it, though, he found that information on how flamingos group together and organize themselves within flocks was sprinkled with anecdotal observations but no robust research. So, he turned to tools that map interactions between humans and tried to apply them to flamingos. One group of researchers, for instance, used cell phone data to accurately predict friendships between students; all they needed was the phones’ location data and the amount of time each spent in the company of other phones. While the flamingos at Slimbridge don't carry phones, they each wear an identifying number on their leg. These allowed Rose to track individual birds and their proximity to others in the flock.

Between 2012 and 2016, he photographed each of the four flamingo flocks at least three times a day in the breeding and non-breeding seasons to see which flamingos clustered together. He inferred affinity or bonding between any two birds if they were regularly observed within neck-length distance of each other. “Flamingos joust and fight with their bill and neck,” Rose says. “So if you are going to let another bird stand next to you within that neck-length distance, it’s likely you’re in friendly space.” He also kept track of birds that rarely crossed this threshold, which he assumed meant the birds weren't on good terms. 

Based on these observations, Rose found that flamingos maintain firm, non-reproductive relations with birds who aren’t their mates—or, in other words, friendships. These included male-male or female-female friendships, and mixed-sex trios and quartets, too, that remained “tight” through the years, he says. Interestingly, in American Flamingo flocks, Rose says he also came across several “social butterflies,” or birds who hung out with multiple small groups. But even these flamingos had a pal with whom they spent relatively more time.

Although the study captured these partnerships during a five-year period, it’s likely that some of the connections go way back, Rose says. Flamingos, in general, are long-lived birds, and some individuals at Slimbridge have lived there for nearly 60 years. 

But why do flamingos develop these long-term friendships? “I think it’s because birds potentially get support from each other,” Rose says. Flamingos likely buddy up with those who help them find food or keep predators at bay, he says. These partnerships appeared more tight-knit in the breeding season, when feeding chicks and protecting nests are crucial for a flock’s survival.

Not all flamingo relations were friendly. Some flock members avoided each other entirely and never crossed paths. A few even displayed signs of aggression when coming in close quarters with individuals they appeared to dislike. In the Andean Flamingos flock, for instance, Rose observed three charismatic males who were “extremely nasty” to each other, even though they were okay with other males being around.

While Rose's findings reveal new insights into flamingo behavior, determining whether such animosity and affinity exist in wild flamingos is a much harder task. The trouble is getting to know birds individually, especially when flock numbers can exceed a million birds, says Felicity Arengo, a coordinator for the International Union for Conservation of Nature’s. Arengo, who was not involved in the new study, has led and been part of several flamingo banding programs in South America that have banded nearly 12,000 birds since the 1980s. “The probability of resighting them again is very small,” she says, which makes it hard to track individuals and their social life year after year. “They’re nomadic; they move to track resources.” However, recognizing that flamingo flocks aren’t homogenous and that individuals have social preferences is an important finding, she says. 

For now, Rose's research might be most useful for zoo and sanctuary managers. Flamingos are often shuffled between zoos to diversify a flock's genetic pool. Rose hopes that when managers pick out flamingos to move, they’ll be careful not to separate individuals that are closely bonded to each other. He also urges zoos to maintain larger flocks, when possible, to provide flamingos a variety of individuals and personalities to form associations with. “I’ve been banging on about flamingo social groups for a long time,” Rose says, “and maybe it will start to trickle in that we need to consider flamingo welfare.”