Personally, I think they duck naturally.

To compensate for this I usually aim 1/3 up from the belly and just behind the shoulder. This year tho, my doe ducked a little more than normal and I got a high left lung hit and my arrow exited through the liver on the opposite side. Normally I hit around mid body.

Others on the board may also advise you to bend at the waist when shooting from a tree stand.

Dick