I was out walking last night when it was very nearly dark. A duck flew overhead, just a little higher than the rooftops - it was repeatedly making a longis reedy quacking sound. A few more went over shortly after, doing the same.
Is it possible the noise they were making was for the purpose of echo location in the dark?
A duck’s quack certainly does echo (people have put ducks in echo chambers to prove it), but I have no idea if the echo is used by ducks. I wouldn’t have thought so, but what do I know?
Such a low frequency sound wouldn’t be useful in the same way that bats echolocate. Bats emit sounds in tens of thousands of hertz, most of which humans can’t hear. Some humans can echolocate, and it gives very coarse navigation. I haven’t heard anything about ducks, and I think most are diurnal, so it is possible but not likely. It could quite probably be a communication signal.
ducks make different sounds when flying, feeding, fleeing, looking for friends.
More likely, it was simply so that the ducks could look for / keep track of each other.
This wasn’t your typical ‘quack quack’ kind of duck sound - it was more a wheezy, reedy sort of thing - certainly with higher-frequency - almost percussive-sounding components. Obviously still not like the ultrasonics used by bats, but I’m pretty sure *I/i] would be able to hear the echo of something like it.
These were flying in the post-dusk evening, visibility would certainly have been very poor - although if they were flying onward to land on an expanse of water, I expect that might be quite visible by moonlight.