Is it possible for bats to become large (roughly dog sized) pack hunting predators while retaining their flight capabilities? What changes to their internal physiology and/or wing morphology would be necessary for this to occur?

The context for this would be a large region of the world which experienced an extinction event that rendered all large ground predators (and herbivores) extinct. All life is earth based, and largely consists of flightless birds, ground sloths and some reptiles. Is it possible for bats to evolve into the niche of large, apex predators?

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    $\begingroup$ Possible? Well, nothing prevents it. Probable?? Not that probable, but author fiat can stretch a loooong way! $\endgroup$
    – Joe Bloggs
    Nov 26 '20 at 21:55
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    $\begingroup$ (1) "Dog size" is extremely ambiguous; an adult dog can weigh anywhere between a few hundred grams and over a hundred kilograms, depending on breed. (2) (Some) birds (the Accipitriformes and Falconiformes) did evolve to be apex predators. Some of those apex predator birds, such as the harpy eagle (9 or 10 kg) or the recently extinct Haast's eagle (up to 15 kg) have body weights comparable with some breeds of dogs, such as miniature poodles. If some archosaurians did it, some synapsids can do it too. $\endgroup$
    – AlexP
    Nov 26 '20 at 21:56
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    $\begingroup$ I think you may want to rephrase your question from "apex" to "large." Electric eels are apex -- nothing preys on them -- but they aren't that large. $\endgroup$
    – Mary
    Nov 26 '20 at 23:35
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    $\begingroup$ The Great Skua, a bird, is an apex predator. The real problem is making them hard to hunt as having no natural predators is part of being an apex predator, and a fair number of critters like to eat bat. BTW, please ask only one question per post. You've asked two: (a) can they become... and (b) what would need to change for them to become? Frankly, you should edit the Q to remove all the "can they become..." and stick with "what to change...." $\endgroup$ Nov 27 '20 at 0:23
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    $\begingroup$ Sounds to me like you want your bats to become more like a certain extinct creature which found itself in a similar scenario. I also advice you to research about Vampyrum spectrum, a species of carnivorous bat which hunts more than insects, and the harpy eagle, an Apex predator which eats sloths. I'll say it now though: evidence of similar events showed adaptations to better hunt on land being selected. $\endgroup$ Nov 27 '20 at 11:04

Depending on your definition of "dog-sized", there already exist bats that large. Various subspecies of the giant flying fox already have a wingspan over 1.5 meters, albeit with a mass of less than two kilograms.

For my answer, I'm going to assume you meant something substantially larger than what already exists out there, perhaps double the wingspan. I'll be outlining some major points for consideration, and suggesting likely changes.

Diet: Most bats are insectivores, but those are small. I strongly doubt that a diet of primarily insects will be dense enough in energy and nutrients if you scale your bats up. I suspect your bats will mostly be hunting small animals, but fishing or eating fruit are also possibilities to provide other options. Bear in mind that bats eat about their own body weight's worth of food daily: these are going to be some very hungry creatures.

It's good news for you, then, that all of those already do occur in bats; not necessarily all in a single specimen, but bats have a surprisingly wide variety in their diet. Most of the larger bats, like the flying foxes, have a diet composed primarily of fruit. Certain bats with specialized adaptations regularly target fish and crabs or frogs. The noctule bat can even hunt birds as they fly! Making your bat larger will probably not do it any harm with such prey, although a dense forest would be more problematic; still, you can plausibly have your giant bat attacking rabbits and birds readily enough.

Flight: This amounts to checking if a wide-winged bat could still fly, and I believe it could. You might lose some maneuverability in raising the wingspan so high, but bat wings have a great deal more flexibility than bird wings; they can probably compensate for that loss. There are birds with wingspans of 3 meters or more, and they can fly; bats can't glide as well as birds do, but I see no reason why a bat of similar size can't fly for shorter periods. Bat wings do tear easily, so bear that in mind: they heal quickly from small tears, but they can't afford to get caught in an actual fight with their prey.

Temperature: This is probably your biggest concern. Bat wings have a tremendous surface area for their size (basically a requirement for flight-capable wings); this is great for shedding heat, but it has drawbacks as well. With that much surface area, they are extremely vulnerable to low temperatures, and bat wings can't naturally grow any insulating hair over most of their surface to try and compensate. Eating huge quantities of food could make up for such heat loss at the cost of needing to be capable of hunting that much, but it's still a huge disadvantage. I wouldn't expect your giant bats to fare well outside the tropics, but that is a constraint on your bats, not a denial of their ability to exist.

Predation: The giant flying fox has eagles and giant snakes as its known predators (not counting humans). From your description, large birds aren't present, and it's not exactly going to shatter your reader's suspension of disbelief if you posit that this area of your world doesn't have snakes in the four-meter-plus range. Even ignoring that mundane solution, if your bats are double the size, they're going to be much less tempting as targets.

Conclusion: Reading up showed me that there was a lot less to change than I first thought. Most of what you're looking for is already present in bats, and your world's extinction event has apparently cleared out any larger competition. I don't think you'll get pack hunting without a lot more changes, because they don't need that for anything they're going to be targeting, but with your world as stated giant flying foxes are already basically apex predators: make them larger, give them an adaptation to hunt small animals, and you're as good as done. Really, it seems like your biggest concern is why the bats even need to get larger at all: perhaps it's to keep off potential predators?

  • $\begingroup$ Thank you very much for this superbly helpful answer! When I had said apex predator, what I meant was something capable of hunting (relatively) large game, similar in size to sheep. I can see that that is somewhat unfeasible, and is largely why I wanted a larger size and a pack hunting nature. (Although, somebody did mention being poisonous or diseased to technically be an apex predator. Maybe something along the lines of the old theory of Komodo dragons?). $\endgroup$ Nov 28 '20 at 1:31

Easy: (to satisfy the title question)

It hinges on the definition of "Apex Predator" Which simply is "a predator at the top of a food chain, without natural predators"

There is no requirement for an Apex Predator to be the biggest or baddest thing on the block, as long as it is not prey to something else.

Just make your bat carry an exceptionally nasty poison, or a virulent disease, that 100% kills anything that consumes a live bat. This will very rapidly covert the bat from prey to an avoid-at-all-costs target, thus de facto rendering it an apex predator.

,but actually almost impossibe:

Ok, let's try to satisfy your actual question.
Can bats become the only real predators, against a vast array of potential prey species, in the absence of other predators. And still retain flight ability in the process?

The largest earth bat masses only about 1.4kg
The main reason for this is aerodynamics. The flexible membrane bat-wing simply does not scale up very well for larger body sizes, in an Earthlike atmosphere and gravity, for an active flyer.

Assuming you are limited to Earth for physical properties, and to Earthlike biochemistry for your bats, the answer is no. You would need to convert them to a more efficient flying structure (i.e. make them birds, with all the weight-saving measure birds use: hollow bones, beaks in stead of jaws, feathers in stead of membranes, etc.. all mass-saving tricks).

Or you would have to fiddle with their biochemistry in some way. Make them capable of greater exertion.

Possibly a better breathing system? Something like the "supercharger" as envisioned by Poul Anderson in his "Stormgate" books. Basically a flying creature with wing-muscle powered auxiliary gill-like "supercharger" lungs, providing much more oxygen to the blood, allowing brief bursts of much greater exertion. You may also need a better or at least more concentrated blood oxygen carrier mechanism.

  • $\begingroup$ Thank you for your comment! It is very helpful! $\endgroup$ Nov 28 '20 at 1:32

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