The Swarm That Got Away

Today at the Farmstead I noticed some bees swarming out in the field. I went in for a closer look and watched them congregate on the branch of a nearby tree.  Being the dutiful beekeeper I am, I promptly collected and empty hive box and made a new bottom board/base. I got my bee hood and brush and pruners and went to "capture them" or so I hoped.  I went back later to check on them and they had left the box. I guess they found some place better to go.