Do Wrens sing in the hypersonic range?

I have observed and videotaped Wrens chirping on my fence. They go through an exagerated body movement that involves them standing up on their legs as part of the effort of singing.

What has been interesting to me is that the Wrens sometimes will go through the same movements at the beginning, in the middle or at the end of their calling, but there is no apparent sound.

I hypothosized that part of the Wren's song is ultrasonic. I haven't found any research suggesting this on the internet, so I thought I would ask you to pass this to someone who might know and/or be interested in pursuing this further.

I would like to, but ultrasonic microphones cost more than I can invest. If you know how I can borrow such eqipment from some nearby resource, I would like to explore it determining if my theory is correct.

I suspect that ultrasonic sound plays a much greater role among many bird species that we are currently aware. It might take a while, because I havent seen may birds of any kind in the last two or three weeks. Prior to that, our courtyard was as active as a nature preserve with up to 15 birds of differing varieties coming there at a one time in addition to several chipmunks and a squirrel.