Both microphones are flowerpot pressure zone microphones, as pictured on the previous page, and connected to a computer which records the calls directly to a hard drive.  The files are then analyzed using GlassOFire, Syrinx, or Raven.  The spectrograms are examined closely and, if possible,  sorted to species (or species group).

 What's the difference between these calls?

Bicknell's Thrush is a higher pitched call than the Gray-cheeked (by nearly 1 kHz - see spectrograms above). There is individual variation, of course, but Bicknell's calls generally sound slightly more drawn out than Gray-cheeked. Although both call notes can sound similar to the human ear (click on spectrograms above), Bicknell's calls can sometimes be heard to rise quickly before dropping in pitch.  By looking at the spectrogram on the right, it might seem as though there would be an audible beginning rise in pitch in the Gray-cheeked's call, too.  Because of its relatively shorter duration, however, the call actually sounds more even than the Bicknell's, with a slightly downward, buzzy inflection.  Different Gray-cheeked call variations may sound like "weerrr", "veer" or "whurr;" sometimes the call does not drop as much and is slightly shorter, sounding like "veee."  Bicknell's sounds like "pteer" "teeeer", or "geeer;" Bicknell's also is not quite as buzzy or harsh sounding as the Gray-cheeked.