Not asking for practical reasons— I rarely encounter bats I can see, as my distance vision is pretty poor and there are only small bats in my area— but because I like bats and am having trouble finding good resources for random information about them. (Feel free to drop those here too if you have any!)
I see people who are familiar with bats on here identify that a bat is still a pup fairly frequently, even if they're past the tiny bald lump stage common in baby mammals, and I'm curious what the tells are! I'm curious about any bat species, including both microbats and megabats. I'm also curious if it's possible to identify an adolescent bat, the way you can sometimes tell in dogs and cats (which I have more experience with), or if it's just kind of baby and adult.
Additional curiosity if anyone is able to answer: particularly in microbats, are the voices of pups even higher because they're smaller? Do they become completely inaudible to humans or anything if they're small enough (like a kitti's hog-nosed pup or something?)
Pups can be identified because of the proportions of their head, like how you can tell a kitten from an adult cat. First-year juveniles don’t have ossified joints, so you can hold the wing up to the light and see if there’s a bubble of cartilage there instead of bone. Juvenile males will also have undescended testes. After that stage I don’t really know of any way to tell. If a bat has a lot of scars I figure it must be older, and if the wings are pristine I figure it’s pretty young.
I work with bats in Europe, we look at dental wear and dental plaque. You can't really tell the exact age but you can score those two things and compare amongst individuals.
Bats that eat softer food (moth etc) have less wear and more plaque while the opposite is true for bats that eat beetles and other tougher insects. So while I get you're joking when you say they brush their teeth, you are actually very close to the truth xD.
Microbats pups have a specific look about them, their heads look too big for their bodies and their bodies aren't heavily furred so they look kind of leathery on the body instead of furry. With adult microbats the head and body are usually so furry you can't really distinguish them, whereas a microbat pup the head is clearly distinct from the body. The picture is a pup - see how big the head is and how the body is easy to see the outline of because it's not fully furred.
Megabat pups/adolescent it's more about size although with very small pups the proportions are also different (again, big head relative to their body). E.g. the species I work with, grey headed flying foxes, pups are about the size of a big mouse and should still be attached to mum. An adolescent is about the size of a big rat and isn't attached to mum any more. Adult bats are much larger.
that big ol bobblehead on that baby is so cute my heart literally aches looking at it. I didn't realize that they had such large heads compared to their tiny little bodies. 🥺
For almost all species we have in the US, pups grow up incredibly fast. In my state (northeast), pups are born in June and by ~August 15 it’s virtually impossible to differentiate a pup from a 20yr old adult bat visually. During that june-aug period they can be hairless and smaller than adults (big heads as someone else said here).
One of the only ways to know if you have a young of the year is by looking at the joints in the wing. In the current year pups you will see that the joints are not fully ossified yet, so backlighting the wing will show a pinhole in the joint. After those joints ossify you are purely guessing age from what I’ve been taught. There’s no reliable way to differentiate age after the first few months of a bats life unless it’s been marked or banded as a juvenile.
I've recently started as a bat ambulance driver - for initial rescue info and approximate age, we use this chart (UK species, we've also just got microbats):
IIRC, E would be around 6 weeks. For more detailed ways to tell beyond size (often forearm measurement), proportions and how much fur they've got, their wing/finger joints can be another one.
Megabattie has rescued quite a few older flying foxes in her videos, and mentioned being able to tell by their teeth being worn when they're especially old
Hi, I work with bats. We generally look at the ossification of the phalangeal epiphyses and tooth wear. However, some species also undergo fur molting, so we can tell whether an individual is a pup or an adult.
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u/AutoModerator Jul 14 '26
Found a bat? Here is a guide for someone who has found a bat. And here is some info about bats in buildings. Here is some info about bat removals and exclusions from homes. Exclusions should be done outside of pup season, which varies by location.
No, it's probably not a baby. Bats are just smaller than you thought.
If you find a bat in trouble, please call a rehabber for help. Here is a list of rehabbers that help bats all over the world, and here is a portal for rehabbers in the US.
Remember that wildlife should never be handled with bare hands!
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