Steve Thomas
Despite all of their "daily chaos, the bats are able to maintain long-term relationships," says the lead author of a new study on bat relationships, Gerald Kerth.
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updated 2/9/2011 1:05:52 PM ET 2011-02-09T18:05:52

As Valentine's Day cards attest, humans value love and friendship that aren't just forged by family ties, common interests or sexual attraction. Now researchers have determined that such human-like friendships exist among at least five different types of animals.

Prior studies determined that elephants, dolphins, some carnivores and certain non-human primates, such as chimpanzees, have the ability — just as humans do — to maintain enduring friendships in highly dynamic social environments. A new study, published in the latest issue of the Proceedings of the Royal Society B, adds bats to that list.

Female wild Bechstein's bats prefer to literally hang out with certain friends while they also keep loose ties to the rest of their colony. Lead author Gerald Kerth told Discovery News that these bat buddies mirror human ones. Despite all of their "daily chaos, the bats are able to maintain long-term relationships," he said.

"We do not work, play and live together with the same individuals all the time during the day and week," he explained. "But nevertheless, we are able to maintain long-term relationships with our friends and our family despite our often chaotic and highly dynamic social lives."

Kerth, a professor at the University of Greifswald's Zoological Institute, and colleagues Nicolas Perony and Frank Schweitzer monitored colonies of the bats over a period of five years. Male bats of this species are solitary, but females roost together in bat boxes and tree cavities. They preferred certain companions over the years.

In addition to resting together, "colony members exchange information among each other about suitable roosts, make flexible group decisions where to communally roost next, groom each other and profit from communal roosting through warming of each other," Kerth said.

The researchers determined that the female bats did not just select their companions based on size, age, reproductive status or relatedness, although older female bats often maintained links between friend subgroups.

Kerth believes the human-like friendships likely exist among other bats living in temperate zones, since these bats often live in colonies that also frequently split and merge, a phenomenon known as "fission-fusion."

"Fission-fusion dynamics with long-term social relationships are also found in elephants, dolphins, chimpanzees and humans," he said.

Jonathon Balcombe, an animal behavior research scientist and consultant for the Physicians Committee for Responsible Medicine, pointed out that female bats even sometimes serve as midwives.

In one documented case, a pregnant fruit bat in Florida was attended by an unrelated female fruit bat, according to Balcombe, who is author of the book "Second Nature." The helper bat repeatedly groomed and hugged the pregnant bat during the birthing process.

"Following birth, the helper groomed the pup, and she and a third female fanned the mother with her wings," added Balcombe.

Other animals with human-like friendships, such as elephants, tend to have large brains, but bats prove that even species with "peanut-sized brains can also have long-term relationships," Kerth said. "This for me suggests that it does not necessarily take large brains to keep track of relationships in highly dynamic societies."

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The discoveries may negate prior theories on why humans evolved large brains and became such a dominant species. Previously, some anthropologists thought this was driven by our need to maintain relationships in an ever-changing social setting. Now it's suspected that other factors must have come into play. In fact, tiny-brained bats may even be better at maintaining friendships than we are.

Kerth said he admires "bats for doing things that I find difficult: making quick and efficient group decisions in a group of 20-plus individuals and keeping social relationships despite a regular mixing of social partners."

"I sometimes feel that this is cognitively demanding for me (since) we all know the embarrassing feeling when we forget the name/affiliation of somebody we haven't seen in a while but who remembers us well," he continued, suggesting that this recently happened to him at a conference.

In the future, he'd like to see if bats ever experience such social faux pas.

© 2012 Discovery Channel

Explainer: Good times of the animal kind

  • Getty Images

    Who knows what's causing this cohort of cubicle warriors to buckle over in laughter, but few humans would disagree that a good chuckle every now and again feels good. Monkeys, dogs and fish get a kick out of life as well, says Jonathan Balcombe, a senior research scientist with the Physicians Committee for Responsible Medicine in Washington, D.C. He has written several research papers and books on animal pleasure, including "Exultant Ark: A Pictorial Tour of Animal Pleasures," due out next year. Click the "Next" arrow above for an overview of good times in the animal kingdom.

  • Man's best friend is full of expression

    David Bolton  /  Morguegfile,com

    Dogs, a slate of research suggests, are full of expression. "Those who live with dogs know that by looking at the body posture and the tail movements and the facial expressions and the sounds they make, we can sort of divine how they are feeling; whether they are feeling up or down, excited or grim or guilty, or what have you," Balcombe says. Even people who haven't lived with dogs, studies show, are able to read dog behavior, he adds. "We can only imagine how well dogs can read dogs, but dogs 'dogamorphize,' I suppose, and being dogs — with their keen sense of smell, for example — they get a lot more information than we do."

  • Horses' heart rates drop when groomed

    Reed Saxon  /  AP

    Look to horses for biological evidence that animals can feel pleasure. Balcombe notes that studies have found, for example, that horses' heart rates drop when they are groomed on parts of their necks and withers. A drop in heart rate "is known to be a response to feeling good and feeling relaxed," he says. In this image, Mike Polder comforts his horse Rowdy who was recovering from a West Nile virus infection.

  • Rats like to be tickled

    Brandi Saxton

    When young rats — the rodents that some humans love to hate — are seen running around wrestling with each other, they are actually in what equates to a tickle fight, according to research led by Jaak Panskeep at Washington State University. The rats, it appears, love to be tickled. His work, cited by Balcombe, shows that rats that have been trained to expect a belly tickle will approach a researcher's hand much more quickly than a rat that knows it'll just receive a neck rub.

  • Monkey massages are calming

    Arthur Sevestre

    Observations indicate that monkeys like to cuddle, such as those shown here, and give massages. Balcombe says these rub downs cause monkey blood chemistry and hormone levels to change in ways "that are consistent with what we would find in ourselves when we are receiving a massage." The biochemical finding, he adds, is another window into how animals experience pleasure.

  • Sexual activity not always for procreation

    Mitch Reardon  /  Lonely Planet Images

    As many humans know, sexual activity isn't always for the purpose of making a baby. The animal kingdom is full of examples of creatures that get it on just 'cause, says Balcombe. Among giraffes, for instance, homosexual activity is often more common than heterosexual activity. And even when the act is in the direction of procreation, Balcombe says that most animals probably don't connect the dots between their pleasure seeking and babymaking.

  • Fish go in for a cleaning

    Gerry Allen / The Swedish Research Council

    Balcombe's studies on animal pleasure are, in part, a pushback against the scientific community's penchant for parsing animal behavior in strict evolutionary terms. For example, the relationship between cleaner fish and their clients is often described as one of mutual benefit. The cleaners get food from the parasites on the clients' bodies and the clients get cleaned. "But I think the reason the fish go there is because it feels good. I don't think the fish clients are aware of any health benefit," he says. "So I do think that's a pleasure driven interaction."

  • Squirrels chase each other for fun

    Arthur Sevestre

    The squirrels shown here chasing each other around a tree are just playing around, according to Balcombe. While play behavior may have evolutionary underpinnings such as learning to escape from predators and tackle prey, Balcombe argues in a recent review paper in the journal Applied Animal Behavior Science that animals "do not consciously play for ultimate reasons: they play because it is fun to do so."

  • Dolphin looks can be deceiving

    Chris Gotshall  /  Reuters file

    Is this bottlenose dolphin happy to be bonding with her newborn calf? Despite a vast scientific literature on dolphin intelligence and scant doubt that they can feel pleasure, Balcombe says little can be gleaned from their facial expressions. Dolphins, he notes, have fairly fixed expressions. "The important thing with interpreting other animal's feelings is to know the animal, to know their biology, to know how they work," he says.

  • A calf runs free

    Connie Pugh

    Whitaker, a calf freed from a factory farm operation, enjoys a good run in this image. Balcombe, who has been a vegetarian for 25 years, says he grew up eating meat and "grew to love it." He stopped his carnivore ways out of concerns for animal welfare and thinks the growing body of research on animal feelings along with research showing adverse effects on the planet's health from animal agriculture will motivate other people to change their diets too.

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