In an alternate Earth, there are no bats. Instead, there are "flying monkeys" (which are actually lemuriform primates, rather like bushbabies or lorises.) And even though they have batlike ears, they don't echolocate. Instead, they hear their way through the nightscape a bit more like owls--their outer ears may be symmetrical, but their inner ear bones aren't. This would allow them to accurately judge the distance of their prey. And just as we humans can be either left- or right-handed, a flying monkey can be either left- or right-eared.

But could this sort of adaptation be useful for roosting in huge colonies on cave ceilings, like some bat species do?

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    $\begingroup$ I'm not sure that passive hearing alone is enough for navigation in complete darkness. Many owls have quite good low-light vision, I note. $\endgroup$ Nov 9, 2019 at 14:44
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    $\begingroup$ Also worth noting that bats and owls hunt different prey, on average. Most microbats use echolocation to target insects - very small targets that would be nearly impossible to see, even with night vision. Owls tend to go for larger fare that can be seen and heard with sharp passive senses, like birds and rodents. $\endgroup$ Nov 10, 2019 at 9:36

2 Answers 2


The great advantage of echolocation is the ability to judge distance. It works the same way sonar works: The bat sounds a chirp, and distance is estimated by the time it takes for the sound from its source, to the object or obstacle and back to the ears of its originator.

Sonar echolocation for hunting as well as hearing you way through has advantages over passive hearing. One thing for sure, you cannot "hear" obstacles just as you can't see without light. Obstacles reflect sounds, they don't make them. Sonar has few helpful uses: time for the sonar chirp echo to come back to the ears gives distance from the object. Loudness difference and time difference between the two ears gives you direction and the doppler effect (change between the frequency of the sound and that of its echo) gives an estimate of your speed relative to the obstacle.

Source: https://en.m.wikipedia.org/wiki/Animal_echolocation

Edit: passive hearing may work in detecting a sound source; a singing cricket, singing bird, or animals fighting. It may not, however, detect obstacles along the way or catching a silent prey on flight. It is less accurate as a means to judge distance.

  • $\begingroup$ So...is that a "yes" or a "no"? $\endgroup$ Nov 10, 2019 at 2:48
  • $\begingroup$ @johnWDailey added in the edit. $\endgroup$ Nov 10, 2019 at 11:16
  • $\begingroup$ No, no, the question is whether or not such ears would allow for colonial living in caves. $\endgroup$ Nov 10, 2019 at 15:58

I think you are mixing up what sensory systems an owl needs to hunt, with what it needs to navigate.

Hunting: The owl is listening for sounds made by the prey. It has those asymmetrical ears to have '3 dimensional stereoscopic hearing' and get a precise fix on where the vole it wants to eat is.

Navigating: the owl is using its eyes to see where it is going. It needs to be able to fly about without crashing into trees, smacking into cliffs or crashing into the ground. Its hearing may help a little with this. For instance, it might hear the rustle of leaves in the wind. Plus that vole it can hear will be on the ground (or just underneath a layer of snow), not hovering in mid-air. However, that hearing is just the icing on the cake. It is using starlight, moonlight and its eyes to navigate.

So, your problem is that in deep caves (the sort bats use) there is no light at all. Even in shallow bits of caves, like those used by Cave Swiftlets (one of the few types of birds to echolocate) there night be some dim light in the daytime, but virtually none at night.

The rocks of the cave do not make a sound, so the owl (or your flying monkeys) cannot use hearing as a passive sense to navigate around the cave.

Cave dwellers use echolocation because it is an active sensory system - you emit a signal and receive an echo back to map your environment. In simple terms, it is like lighting your way with a torch: emit the light beam, use that light to see what is in front of you.

The owl type of ears plus echolocation would work very well in caves, because the owl's asymmetric ears will give it just the same very precise information on where the cave walls are, as they do in the real world about where the owl's prey is.


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