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Essentially, I have a flying predatory creature in my world which is roughly the size of a raven and hunts at night, relying quite a bit on sound for echolocation in tighter spaces, hearing for both prey and predators and for communication. Because of this, I wished to give them large ear-like structures, but there are some problems with the context the creature is in:

  • the creature is not from earth and has many similarities with arthropods overall, with most of its head, apart from most of these ears, being covered by a hard exoskeleton, so I didn't want to give it external ears too similar to mammalian ones.

  • these creatures have natural predators, so I wanted their ears to be usable to look bigger and more threatening, potentially with eye spots or bright patterns.

  • I wanted the ears to be somewhat compressible, both to hide said warning patterns while trying to camouflage and to make them less likely to be damaged or get in the way when not used to actively listen for something.

The solution I thought of was a flexible frill-like structure with 2 main, flexible support "rods" on each side of the head (measuring around 5 centimeters in length) that could spread out like a satellite dish, with a net of muscles on the membranous part changing the shape of the ear to further help it amplify sound at certain frequencies of interest to the alien, like what you'd see in pterosaur wings or an octopus' skin. Rough draft of what I mean below, blue being the "ear" while retracted close to the body and orange the structure spread out and in use:

enter image description here

That being said, I haven't really heard of anything quite like this before in our world, the closest being African elephant ears, which can't quite compress and have their sized justified in part due to thermoregulation. Other than that, I couldn't find anything really saying whether such an arrangement could actually be good or just a waste of energy.

That said, could such a type of external ear work?.

Specifying what I need: I'd like to know if it's at least somewhat functional without being terribly impractical, and whether this design could be still salvageable to some extent in case it's not.

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Some notes on size and frequency

Your creature won't fly with that one

(Note: below will be of consideration with flying animals, but given the fact this anthropod has the size of a raven, it will be less of a concern)

The issue of the reflector in your opening's drawing is the amount of air resistance, placed in forward direction as a collar around the creature's neck, similar to Fred's lizards. A flying insect can't carry a fleece like that while flying forward.

Go ultrasonic, to reduce the size of the receiver

Let's assume your arthropod is a centimeter, or a few centimeters. Insects usually produce sounds around 4-12kHz (see this article). When the sound emitted is e.g. 10kHz, your wavelength will be about 0.045 meters. A suitable parabolic antenna for that has a diameter at least about 0.015 meters to actually amplify the sound. Preferably it should be larger, a multiple of the wavelength. See this article. So.. choose your echolocation frequency wisely, go high up ultrasonic.. 40kHz would reduce the minimal diameter of your parabola to 3mm. With "collar antennas" of 10mm you'd have about 10x amplification.

Flexible ears

For echolocation and to prevent the issues with flying, you could consider introducing flexibility. Bats have that. Allow the animal to change the shape very quickly. See this article.

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    $\begingroup$ Sorry, it seems I didn't express myself properly and forgot to add an important detail: my creature has many arthropod-like traits, but is fairly large in size, being about the size of a raven. The "ear" structure rods would likely measure somewhere around 5 centimeters in length. Would that be too big to be practical? $\endgroup$
    – ProjectApex
    Jun 25, 2022 at 19:04
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    $\begingroup$ Thx, I've added a note. Scale up the formula, you could use a lower frequency. Or have more effective antennas. Your creature would be same order of size compared to a bat, would not need extremely large "ear fleeces". It all depends on living conditions. Bats live in confined spaces, they need fast and accurate echolocation. $\endgroup$
    – Goodies
    Jun 25, 2022 at 19:22
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Frilled ears similar to the neck frills that frilled neck lizards from northern Australia have are possible. If they are shaped correctly they can be parabolic and focus the sounds to the ear hole similar to how parabolic radio dishes work.

The other option is to have expandable ears that become enlarged when bodily fluid is pumped into them.

enter image description here

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  • $\begingroup$ Are you sure ? Aren't these "ears" meant to look like large eyes, to scare off predator birds ? or leafs, to camouflage ? Maybe I'm mistaking, but it occurred to me that the word "ear" does not appear in the Wiki topic you link.. $\endgroup$
    – Goodies
    Jun 25, 2022 at 17:23

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