Depends how serious you are to spend significant dollars for something that may only produce bird calls - that said I'd prefer a parabolic opposed to a shotgun mic since its semi directional & able to gather more sound.
"Always keep your mind and heart open..." - Henry Fonda
The big question is what do you want to capture? So in an ideal scenario, what is the evidence you wish to capture? A howl? A scream? So assuming that you have the audio evidence you wanted - how do you show that it is a. genuine b. from bigfoot c. not from another source Sadly, I think that although useful when combined with other evidence, audio evidence is the least persuasive of any of the evidence that BF researchers can gather in the field. With that said, they make GREAT toys to listen to your kids Richard
-One step, two step, three step ... Wait, I don't have size 26 feet?-