I was impressed by this at RSPB Old Moor. I suppose I shouldn't have been surprised that solid wood makes a note because of xylophones. And it has just struck me that xylo- and xylem must come from the same Greek root for wood. The longest piece was about 90cm long. That would be half a wavelength so f = v/lambda = 230/1.8 = 130Hz which seems about right - a low audible note.
