Used to be, us old-timers could score flutterfly plop on a whim. It was all over the place and no one wanted it. Now, I've been combing the mines for two days, and not a poo to be plucked. Constipated flutterflies, I fear?
FWIW, I think the scarcity of free-falling plops has to do with the reset. When guano was first made into a fertilizer in beta, so many of us had huge surpluses of food that we didn't have as much need for it to speed things up. There was also a period of time where crops had a much shorter grow time, but that was changed not long after guano was made useful.
I also think 3 planks gives you some guano? (I forget the exact amount, it wasn't a lot though). And a decent amount does still fall about, it probably just gets picked up most of the time since there are so many people mining.
three of most stuff gets plops. just like piggies, except they will plop from eating more kinds of things than piggies do.
the most plops I ever got at a time was three. but that's when i gave them all of something by mistake.