Over on YouTube user Jan de Jong has uploaded a few screenshots and sounds on a video which shows that he was able to receive the ultrasonic sound of bats by connecting a small piezo speaker to an SDRplay RSP1A.

The piezo speaker used in reverse as a microphone appears to pickup bat echolocation sound waves which are typically between 20 to 200 kHz. The piezo is resonant in the 40 - 55 kHz range and converts sounds from that range into electric pulses that can be received directly by the RSP1A.