“Hey! I didn’t see you tonight, were you checking out that new place for dinner?”
“I was. But don’t bother, it wasn’t great and I’m still hungry.”
“Sorry about that! But there were lots of chickens where we went, so we got more than enough food. Want some?”
“Oh, that’d be great!”
“It’s the least I could do because you shared last time. How are your pups, are they hungry?”
“Oh, they’re fine, they went along with some friends and got food, but thanks for asking.”
This is a common enough conversation between human friends, but you may be surprised to learn that vampire bats have the same kind of conversation. If a bat goes hungry for more than a couple of nights, it can starve. That’s why these bats often share food by regurgitating part of their blood meal for their hungry friend. And sharing isn’t limited to family members—bats share with unrelated individuals who, in turn, share with them.
Researchers have been intrigued by the way vampire bats build social relationships, share food, and groom each other. They originally assumed that bats kept track of who they shared with, and food sharing was based on a tit-for-tat kind of “reciprocal altruism.” There is some evidence of this, but the truth is even more interesting. Food sharing is actually more like the kind of relationship that humans have with their “besties.” You know that your best friend will pay you back sometime in some form, so there is no need to keep track. And like humans, bats with more friends do better because they have a wider network for support if they lose a close companion.
When you think of most species of bats, you think of them clustered tightly together. They are definitely animals who appreciate a good cuddle, so it shouldn’t come as a surprise that friendships are an important part of their lives. Males are often more independent, but females form close bonds, often grooming each other and helping raise each other’s young. There are even reports of bat “midwives.” At Wild Things Sanctuary, we have often observed pregnant Big brown bats being attended by other females who cluster around the mom-to-be to keep her warm. Once the baby arrives, these “aunties” stay close by. In the wild, females will babysit each other’s young while the mom goes out hunting, even letting the baby suckle (the babysitter may not have milk, but it appears to give the baby comfort).
Sassy (left) and Marathon, two Big brown bat females, were best of friends at Wild Things Sanctuary. They were always together, and here Mrathon keeps Sassy warm just before Sassy gave birth to twins.
Photo by VM Campbell.
Bechstein’s bats in Germany have demonstrated other ways that bat friendships are like those of humans. These bats live in colonies and appear to exchange information about things such as suitable roosts and good hunting grounds. They groom each other, keep each other warm, and make flexible group decisions about where to communally roost. Members know all the individual bats in their colony. But look a bit closer, and you’ll find something even more revealing: one-on-one relationships. Individuals prefer to hang out with certain bats, and maintain these long-term relationships despite an often busy and dynamic social scene going on around them. These bonds are not based on age, reproductive status, or relatedness. Older females even have a few friend “subgroups,” in the same way that we may have several groups of friends who aren’t necessarily close themselves. Only a handful of other species have these kinds of multi-level friendships that are maintained despite regular splitting and merging of groups, among them, elephants, dolphins, humans, and a few other primates.
How do bats recognize each other? They use sight, smell, and voice. That’s right: bats recognize each other’s chatter even though it may sound like a lot of noise to us. The Greater sac-winged bat’s echolocation calls contain information that includes individual ID, gender, age, and even group affiliation. These vocal signatures help male bats avoid rivals and bonded pairs to find each other. When a lone Greater false vampire bat lands and calls, it is joined by members of its usual night roosting group. And these bats not only respond with more enthusiasm to their friends’ calls, but can discriminate between new bats, old bats, and old bats making new calls. They also have a cute little way of touching each other to say hello, much like pals tapping each other on the shoulder.
Bat calls can also broadcast a lot of social gossip. A noisy colony of Egyptian fruit bats is a cacophony to us, but to the bats it serves as a rich information exchange about who is calling, what they are calling about (food, mates, a need for space), and sometimes even which bat is receiving the information. Recent work shows that when a young bat moves to a colony, the newbie learns that colony’s way of communicating—it is not something that they are born knowing.
JanisJ (left) and Bobby McGee were found roosting together in an attic this past winter. Because they were rescued together they shared an enclosure at Wild Things, and even learned how to eat out of a dish together. They had very different personalities, JanisJ being a bit more bossy, but that didn’t stop them from always roosting side by side. Photo by VM Campbell.
At Wild Things Sanctuary, once a recovering patient has gone through quarantine, if they still need time to recover they are placed with others of their species. It has been remarkable to see how relationships are formed and how some bats always choose to roost together, while others may always get in fights (and then are separated). I joke that part of my bat rehabilitation work involves social planning! I’ve seen a bat mourn the loss of a roost mate, and that same bat be encouraged to fly again after making a new friend.
So, if you ever happen to eavesdrop on a group of bats chattering away, consider that in all the noise they may be gossiping about you, or perhaps coming up with a plan on where to go to eat all the insect pests that are so bothersome to us. And next time you come across a bat, treat it kindly and know that like you, it has friends and family waiting for its safe return home.