I don’t know if you guys have noticed this, but I’m a pretty big fan of bats. I’ve been meaning to do a grand ole post on them for a while, and this seems to be the perfect season to do it. So I’d like to talk briefly about the incredible diversity within order Chiroptera.
QUICK BAT FACTS! Did you know….
- Bats comprise about one-fifth of known mammal species?
- The smallest known mammal is a bat? (Well, there’s also a shrew contender, but we’re going with the bat today.)
- The largest bats have five-foot wingspans?
- Tequila wouldn’t exist without bats? (One species pollinates the agave plant it’s made from.)
- Some bats have nipples in their armpits?
- NO bat species is blind?
- Bats can live over 20 years?
- Bats are highly intelligent, social animals?
- THAT BATS WILL NOT LAND/GET TANGLED IN YOUR HAIR, EVER, STOP BELIEVING THIS MYTH
Okay, let’s learn about bats.
Have I mentioned I’m a fan of bats? I actually had a job at one point where I helped mist-net for bats for biological surveys. Here’s me and an Eastern red bat (who is absolutely thrilled to have his picture taken).
Look at that awkward primate… anyway, bats. There are around 1,240 known species and probably a great deal more that are unknown. Just this past September, five new species were identified in West Africa. FIVE new species! And this April, this awesome-looking pied bat was discovered in Sudan.
Basically, there’s a hell of a lot that we don’t actually know about bats, aside from species we don’t even realize exist. They are of course the only mammals capable of true, powered flight. Check out these wings!
(Photo by Oren Peles.)
As you can see, each wing is made up of elongated finger bones with a fine membrane stretched between them. It’s hard to describe what the membrane feels like to the touch- it’s soft, smooth, and supple, kind of like plastic wrap without the stickyness. The official scientific word for the membrane is patagium, by the way.
Actually, though, what fascinates me most about bat wings is how tightly smaller species can fold them- look at the photo of the bat below.
(Photo by A. V. Borissenko.)
I’ve handled hundreds of bats and gotten to manipulate their wings and it’s still hard for me how to describe how that folding works, physically. Basically the fingers come tight together, and the last third folds under and slots into a kind of groove along the bat’s forearm.
There’s another singularly weird aspect of bat anatomy and flexibility that you may or may not have noticed. Their knees bend in the opposite direction as every other mammal.
This aids in angling the membrane between them when flying/scooping up insects, but does make it a bit harder to walk. Most bats can only manage thisscuttling crawl, which is still fairly useful for climbing around rough surfaces like cave walls or trees.
There are some pretty good walkers, runners, and jumpers in the bat kingdom, though. The best-known one is the vampire bat, but probably the most skilled walker of all is the New Zealand lesser short-tailed bat, which actually hunts insects in tiny, ferocious packs on the forest floor. No really, let David Attenborough tell you about it.
Bats are an incredibly diverse group, physically, from the tiny Kitti’s hog-nosed bat, with a wingspan of less than four inches to the gigantic flying foxes.
Bats have been traditionally split into two suborders, megabats and microbats. Megabats cannot echolocate (with the exception of the rousette bats) and eat fruit, nectar, and pollen. Microbats echolocate, tend to be smaller (there are exceptions) and most species are insectivorous.
Relatively recently a new system of classification has been proposed, the yinochiroptera and the yangochiroptera (see what they did there) that shakes things up a bit and resolves a few phylogenetic questions, buuuuuut I’m not really going to go too much into it all. I’m not much of a taxonomist.
Instead let’s look at more physical diversity in bats!
I’ll be up front with you. Some bats are not that cute. Your cute bats tend to be among the flying foxes, which as the name suggests have little foxy faces. (Like the babies in this famous video from the Australian bat clinic.)
(Photo by Elbidio Latorilla.)
They also do that ‘dracula’ wing thing. Microbats don’t do that. Microbats also tend to have some of the weirdest-looking faces due to the fact that they echolocate. It can be as simple as very big ears, like this spotted bat.
Or this Townsend’s big-eared bat.
The function of big ears is pretty obvious: you hear more things. These bats are using their hearing to catch the echoes of the noises they make bouncing off of tiny flying insects.
Watching bats hunt is incredible, by the way; you will not believe how fast and maneuverable they are in the air. I’ve seen bats do a complete about-face in midair just centimeters from a mist net, and I’ve had the pleasure of having bats hunting the insects attracted to my headlamp swooping around my head.
Now, sometimes bigger ears isn’t the way a bat species chooses to enhance its echolocation; sometimes it gets weirder. Like horseshoe bats.
(Photo by Lylambda.)
You may or may not have noticed that something weird is going on with that bat’s nose. That disk-like growth actually serves to enhance the bat’s echolocatory cries, because they actually produce them from their nostrils. Yes, really.
Female horseshoe bats also have a set of false nipples around their vulva that newborns hang onto after birth, because why not.
Speaking of using the nose to make sounds, have a look at this hammerhead bat.
These bats actually do NOT echolocate, being megabats. Instead the males use those outsize shnozzes to honk and buzz to attract females. Extremely sexy.
Since we are still on the subject of noses, let’s examine this sword-nosed bat.
I’m assuming that whole nose bit has to do with sound, but I couldn’t find any official scientific speculation on it. There is just a point when there are too many bats with too many weird things happening on their bodies for biologists to keep track of, I guess.
Now, some of these bats are a little ugly, depending on your taste, but we haven’t really scratched the surface yet. Now we go to some of our more… wrinkly… friends. Have a look at this ghost-faced bat.
I have to admit that I actually find this bat a tiny bit cute, somehow. But anyway, it may be attempting to achieve the same thing an owl does, with its flattened, disklike face directing sound to its ears. It’s slightly more attractive when an owl does this with feathers instead of flaps of skin, though.
Now let’s… let’s go a bit deeper. More weird wrinkles. The visored bat.
What is it doing with that weird nasal plateau, especially given that it is a megabat and therefore does NOT echolocate? We just… we just don’t know.
Alright. I saved this one for last, and then we’ll go back to some cuter bats. Are you ready? I’m not kidding, this one you really need to prepare yourself for. Take a deep breath.
I give you… the wrinkle-faced bat.
Ah yes, nature is amazing. These are another species of fruit-eating bats, which surprisingly fall under microchiroptera, within the leaf-nosed bats (vampire bats are in this group too!)
Fruit does not tend to need to be echolocated at, so the skin flaps aren’t for that- they seem to be related to attractiveness in males (ie, the more hideous, the more attractive they are to females). The bats also have mouth pouches for carrying fruit and a powerful bite, believed to help pierce tougher fruits, but that could also assist them in murdering you in your nightmares.
Let’s get away from the wrinkly horrors now and briefly discuss diversity of diet. I’ve already talked about bats that eat insects, fruit, pollen, and nectar. Speaking of nectar, here’s a video of the tube-lipped nectar bat, which has a tongue 1.5 times as long as its body.
Speaking of tongues, the Pallas’ long-tongued bat has one that’s covered in bristles. But the bristles aren’t just there. No, as it laps, the bat actually engorges its flaccid bristles with blood to help trap the nectar.
Anyway, the things listed above aren’t the only things bats eat. Specifically, insects aren’t the only prey bats hunt. There are species, for example, that specialize in frogs, like the fringe-lipped bat. Other bats go for fish, like the accurately-named fish-eating bat.
But of course, there are also bats that eat lizards, birds, and small rodents. There is even a group of bats that enjoy eating other species of bats– the false vampire bats. If you ever read the Silverwing series, this is the species of the main villains. (The narration in the linked video is misleading, the false vampire bats do NOT drink blood the way true vampire bats do.)
Of course, we all know the other, more macabre dietary choice some bats have, which I’ll get to in a minute, but as a lead-in let’s discuss what bat social behavior is like.
Most bat species are highly social. Species that live in colder climates hibernate in huge colonies that can number in the thousands or millions. Bracken cave in Texas hosts one of the largest known colonies of free-tailed bats, numbering from 20-40 million.
Here’s a video from BBC about this colony (shows a bat being born/a baby bat being eaten by insects, if that makes you uncomfortable).
The social structures bat species employ are as diverse as their physical forms. There are polygynous harem species like the vampire bat, lek species like the hammerhead bat (a lek is where groups of males come together to perform song and dance to attract females, who then tend to mate with the best singer in the bunch), totally promiscuous species… There are even a few species that may be monogamous, including the Dayak fruit bat, in which both males and females produce milk.
The strongest bonds are obviously between mother and infant in the bat world, as the pups are born hairless and nearly helpless. Some, like the free-tailed bats, are left behind when the mothers hunt; others are actually carried by the mothers as they fly, like this Jamaican fruit bat.
This is particularly impressive when you consider the fact that bat babies are often born weighing up to 1/3 of the mother’s body weight.
Most species of bats only have one offspring at a time, but a few, like the Eastern red bat, have two. And yes, this is a species that carries its babies when it flies! Red bats are incredibly strong fliers, in fact; they can even take off directly from the ground.
One would expect an animal with a small size to have a short lifespan and many offspring at a time, like a mouse, but bats are fairly long-lived (20 years on average) and usually have only one pup each year. This contributes to their high social intelligence- each bat can recognize its favorite individuals in these huge colonies- but is devastating when confronted with diseases like white-nose syndrome, which is now tearing through the bat colonies in the U.S. They cannot get their numbers back up quickly enough to recover.
Many species of insectivorous bats split into smaller groups during the summer- large groups of females and their new pups, and smaller groups of males. Caves are not the only resting places for these summer colonies; more often than not they will creep under tree bark or into knotholes. The red bat even sleeps buried in the dense leaf litter on the forest floor.
Mothers and daughters tend to stick together, while males eventually leave to join bachelor colonies (in hibernating bats, these will join up again during the winter migration). In at least one species of bats, Berchstein’s bats, grandmothers are fairly important matriarchs, directing their daughters and their granddaughters where to go and whom to associate with on a nightly basis.
Some bat species are even known to have vocal learning, a trait generally reserved to humans, cetaceans, and some birds. (Here’s some pitched-down audio of a Mexican free-tailed bat courtship song.) Cries are different between different colonies, signifying different vocal cultures, and there’s some evidence that bats can recognize individuals by their voices.
Culture is not just represented vocally; there’s a good chance that foraging techniques are transmitted between bats as well. One study examined fringe-lipped bats responding to the vocalizations of poisonous and non-poisonous anuran species. The bats that were allowed to observe an experienced bat responding to the cries (i.e., eat the non-poisonous frog, ignore the poisonous one) could differentiate between them in only about 5 trials, while bats that had no one to observe took about 100 trials to figure it out. That’s a huge difference.
By the way, one study has found that several species of flying fox pass the pointing test with flying colors; in other words, bats can quickly learn to read and understand human gestures.
But social intelligence and social bonding can go far beyond any of this. Bats can show a sort of kindness and willingness to cooperate that is rarely found in any but the most social of species. I think many people, taking classes on evolution for the first time, are surprised at the organism that invariably comes up during a discussion of altruism: the common vampire bat.
…But the kindness of vampire bats must wait until the next post.
Good Places to Learn More about Bats
About White-Nose Syndrome
White-nose syndrome is a European fungal infection that was inadvertently introduced to American bats in 2006. It has already killed over 5.7 million bats in the US.
White-nose syndrome attacks hibernating bats, causing pain and skin irritation that awakens them from hibernation. Prematurely awakened bats then die of starvation and exposure. Since hibernating bats huddle together by the thousands, the fungus quickly spreads and tears through the colony, causing 90-100% mortality.
(Photo by U.S. Fish and Wildlife Service.)
Two species of bats that the fungus affects, the Indiana bat and the gray bat, are already endangered, and it continues to spread bat-to-bat throughout the east coast of the United States and Canada.
For more information, and ways to help:
From Bat Conservation International:
When tens of thousands of bats emerge at sunset or are seen tightly packed along the walls of a cave, their sheer numbers can leave an impression that bat conservation isn’t particularly critical. We must remember that the bats we see in such great numbers are usually the “Lucky Bats” that enjoy some measure of protection at a specific site. They may be terribly vulnerable at other roosts or along migratory routes. And they may, in fact, be so crowded because other roosting options have been lost and this is all they have left.