I sometimes play with sound analysis software.  I have placed a freeware
version on my FTP site and will keep it open for a while.  It will take a
.wav file and produce an FFT sonogram in color or greyscale.  Time is the X
axis, frequency is the Y axis, and intensity is color.  At the top of the
chart there is an intensity-time plot.  It takes some practice to interpret,
but if you are looking for pulsed sound at say 250 Hz, it will be visible.
The difference between human voices or even two birdcalls is easy to see.

You will still need to collect the sound with a microphone and sound card.
A preamp and combination of high pass/low pass filters will be a big help,
to cut everything below 150 Hz and above 4000 Hz (to get a cleaner signal),
but if you do that, you might as well make something similar to the
Apidictor box.

The circuits to make a dedicated audio preamp/filter/headphone driver
similar to the Apidictor should cost less than $40 USD considering that good
op amps cost less than $1 USD.  I have not designed one but Markham's
"Electronic Circuits Manual" has suitable bandpass circuits that can be
kludged up.  The whole thing would probably fit in a band-aid box and run
off a 9V battery.

The sonogram freeware is on my FTP site at
ftp://ftp.ma.ultranet.com/pub0/d/dnbrown/public_html/

It's called gram.exe.  It runs on Windows 3.11, I don't know about other
operating systems.  If you access the FTP from a browser it will rename the
.exe file as .htm, that's OK, just rename it after you save it to disk.

Turtle Systems makes pretty good audio analysis tools.  I don't know how
much they cost, I bought mine at a yard sale for a few dollars.