I remember an interview with Neil DeGrasse Tyson and Richard Dawkins on some show in America but they were suggesting that it could be possible for ultrasound to be translated into colours by the brain - almost like seeing in colour. Potentially then different organisms could be assigned different colours. However that is a guess from something I heard. I am no bat expert and have not looked for any other evidence. I just thought it was interesting at the time, so I remembered it. Hopefully you are able to find something of value!

https://www.youtube.com/watch?v=9RExQFZzHXQ 

44 minutes ish 

Maybe they can distinguish the different size and shape from the echoes, bigger than them means danger, strip means it may be a snake.

Google "human echolocation". I saw a television show with about a 10 minute segment on Daniel Kish, a person blind from birth, I think, that taught himself to use echolocation to "see" in a rough sense. But it was very impressive. He could distinguish size, shape, density, hardness, and whether something was moving or standing still. He could navigate around vertical poles, but complained that those thinner than about one inch were hard for him to detect, mentioning off-hand that bats could detect and avoid even a thin wire.

I suggest starting with human echolocation, because humans can describe for us in great detail what information *they* can glean from echolocation, and as Daniel Kish mentions, I suppose that bats detect one or two orders of magnitude more.

Bats have to "see" with echolocation with sufficient speed and resolution to catch a moving mosquito with both themselves and their prey moving (and flapping) in three dimensional flight, in the dark. That gives us a minimum resolution (think "pixel size") and frame rate for their echolocation. I assume (after listening to Daniel Kish) that echoes are unique for feathers, flesh, claws and beaks. I assume bats can distinguish profiles. It would be astonishing to me if all that information is not processed in their brain to distinguish not only predators, but different kinds of predators, just as we would with sight.

First we got to think in the size; bats that prey on insects will adjust their preying behaviour depending on the size of the prey, the more body mass of the bat, the bigger is prey, and the lower the freqency of the bat call. So the prey will appear as a glint within the returning echo. But bat predators are certainly bigger than the bats, so by means of echolocation, a bigger object in comparisson to the prey of that bat species would look just like the cluttered background. So the bat detect its predator by eavesdropping, the bat knows perfectly well its predator vocalizations, and it goes in the same way for the predator, that eavesdrop his prey. It's a mortal race.

I have to disagree with Carlos. Bats have to recognize objects larger than themselves all the time. They avoid trees and power lines that are yards long; they navigate away from their roosts to feed and back to their individual roost, in the dark: Certainly they recognize bridges, caves and the interior "landscape" of caves that lets them find their young to feed. In flight, they avoid each other despite flying in thick flocks. I doubt their senses are limited to the size of their prey, and just from a survivalist point of view, I doubt predators fade into the background. Identifying a predator that can end their life has got to be at least as important as securing another bite of food. Small cats that feed on mice and birds climb trees to get away from the big wolves that would devour them. With the exception of some insects, worms, tiny marine animals and other tiny brained organisms, I think nearly every species with predators has to recognize and avoid its predators, which are usually bigger than their prey.

I don't know if you get me wrong, but all the larger items that you mentioned above, are stationary landscape elements, wich the bats can recognize and remember. It is true that in flying duty, bats can avoid each other, and there is a recent research that mentions a kind of "traffic rules" in bats wich states that an individual can follow the track of another bat without crashing. And that sensorial limitation is not due the size of prey, rather it is impossed by the ecomorphology of the bat, i mean the shape, length and width of the wings, aspect ratio, body size, flying speed, and so on. That is what constrains the bat-prey interactions. Now, with bat predators the matter is that they chase the bats; let's talk about bats that prey on bats: Vampyrum spectrum or Phyllostomus hastatus; they chase little insectivorous bats, wich are hunting insects. If we think about the little bat, they definitely will not face its predator (this just because the echolocating bat need to face the target of echolocation, so the signal impinge the insect target, and the echo bounces towards the face of the bats. Under this point of view, there is more chance of survival if the bat can eavesdrop the vocalization of its approaching predator and fly away, than flying towards or facing the predator just to make sure what it is by the means of the bouncing echo. So i did not mean that bats can not recognize their predators at all. But in this case is more important listening than crying loud.

Hi Carlos. Maybe I did get you wrong, I am disagreeing with your statement that "a bigger object in comparison to the prey of that bat species would look just like the cluttered background."

I do not study bats but I am fairly well read on evolutionary strategies, and that statement does not seem plausible to me. Like any implausible claim, I'd need to be convinced by experimental evidence.

I do agree with the idea that often the predator would be behind the bat and "eavesdropping" would be a likely evolutionary strategy. But nature isn't all straight lines, and on TV I've seen bats in highly acrobatic flight. I presume those acrobatics are a necessity in hunting flying insects, so I doubt any predator can maintain a perfect position behind the bat it is hunting and out of its field of echo. And even then the predator would most likely still be in front of other bats, reflecting their echoes to them. So first, it would help the victim to recognize any "glimpse" of a large flying object that appears even briefly in its field of echo, and second, it would help other bats to recognize a predator ahead of it chasing another bat, and turn tail and run, and perhaps to sound an alarm, since bats are social creatures (they will regurgitate to share food with bats unlucky in the hunt).

Given all the machinery of echo location already evolved, these abilities seem pretty plausible to me and hardly more than common pattern recognition, so I would be very surprised if experiments showed that an active, moving predator looked "just like the cluttered background" to a bat, if it caught a predator in its field of echo. I do not have the expertise or time to research that any further, so I will leave my comments at that.