[mou] marsh bird(?) call question

[Thomas Maiello]

I have been slogging it out along the marshes lately - the mud is  
worth it without the bugs.  Out in the middle of a relatively narrow  
band of cat tails between the muddy areas and the lake, I have been  
hearing a sound like the beginning of a cat growl.  I thought some  
type of frog but the sound is low pitched and irregular - not like  
someone trying to attract a mate - it is more like something just  
saying I am here and stay away.  The area is rife with pheasants,  
herons, egrets, and redwings but even with the birds flying over the  
calls stays the same and sporadically irregular.  Any ideas or am I  
dreaming of birds and labeling frogs?

Thomas Maiello
Angel Environmental Management, Inc.
Maple Grove, MN