It puts my parakeets to sleep!!! They can not keep their eyes open!
Also, fascinating to watch the “Exact 40 Hz Gamma Brainwave audio used by MIT to prevent Alzheimer’s” on a spectral analyzer, my favorite being Android “Spectroid” with traditional chart and waterfall presentations. And it seems to be one of the most directional sounds I have ever encountered, at least while playing on my phone. If it turn the phone off-axis in the slightest my perception of the sound volume drops considerably (but then I’m almost 70 and 10 khz is getting up there). But I’m sure the birds can hear it fine.
Also, the perceived volume has to be pretty high to make me sleepy. If the volume is only that of say a radio playing in the background it doesn’t. But if the phone is pointed right at my ear from a foot away or so it does.
It looks to me like the clicking goes all the way down to about 1.2 khz.