I am pretty sure you don't NEED a bone saw and/or to break the pelvic bone, you could just core the anus, and pull through the cavity I believe ( please feel free to correct me) but does having one make it easier?
Thanks
To the OP: Good for you on getting into hunting. A season with awesome experiences is still a successful season :thumbup:
My take on your original question is that the bone saw is not a necessity for the field work, but it is sure nice to have. Especially on those days where you're extra tired/exerted or taking a big animal apart to get him out, and you just can't get those joints to pop apart right. However, there are some things you can do to lessen the need for a saw on the days you find yourself without one:
-As discussed, the pelvis does not necessarily need to be split to do the gutting. However, if you prefer to split it, I have split the pelvis with a knife, hatchet, wire saw, and bone saw, and find the wire saw or bone saw easier to control so as not to bust the bladder.
-The leg joints, after you learn where to cut with the knife, can be cut into, and then busted over your knee or rock/chunk of wood etc. to remove them. The joint on the rear legs is always a little farther down the leg than it seems it should be, maybe by an inch or so. If you hit the joint it is very easy to bust loose. Front legs bust right in the knee, and the tendon on the back of the knee is the toughest thing to cut through.
-The ribs can be split with even a plain-edge knife if you hit the joints right. Instead of trying to split ribs up the center, move to one side (doesn't matter which side) and split the ribs by hitting the joints where the ribs connect to the sternum. They are not hard to split this way. The most difficult one to split, though, is the one closest to the neck. If you have trouble on the last one, try moving back toward center and you should get it. A word of caution, if I get any cuts during the process, it is usually from a dang rib!
-The head can be removed with a knife as well IF you hit the large joint that connects the skull to the neck, and IF you come at it from the throat side. If you try it from the top, then use a saw. This joint is a large 'round' joint. As you cut in, put pressure to bend the head backwards and put the tip of the knife down into the center of the joint, cutting left and then right. Keep putting pressure and as you cut the head will come away and you can finish cutting whatever flesh is needed to remove it from the neck.
I can't think of other cuts you would need a saw for during field-dressing unless it's to remove horns from the skull, but that is obviously not a necessity in the field. I hope this helps, and that I haven't covered things that are too obvious.
Oh, and good luck!! And as always, pictures please!