Sensational dove production used by many pros, including Tony "Senor Torino" Kardyro, as written up in his book, "Dovetail Deceptions."
A bag is shown to the audience to be empty by unzipping its bottom, placing both hands through the open bottom and giving the bag a twist. The zipper is closed and the dove is then produced from the bag.
It appears to the audience that nothing, let alone a live dove, could be in the bag after seeing the way it is shown empty. Self contained, no body loads.
This one is pre-owned, but was only used a few times in practice. Clean and in perfect shape.
Take a look at the video of the dove act of Tom and Sherrie. They feature the zipper dove bag at about the 5 minute mark.