The other day i caught a nicely sized swarm and dropped them into a nuc. I only had one frame of foundation at that moment.(should've been more prepared) So I put the frame in with them and went to my hives and pulled out a nice frame of honey and pollen. I then returned to the swarm in the nuc and added the drawn frame along with the remaining frames of foundation that were missing.....Closed everything up and let it alone. A few hours later the swarm flew leaving behind a handful of bees in the nuc. My only thought was that upon returning to the nuc the second time to add the remaining frames, i used a few puffs of smoke to help move the bees off where the frames rest on. Did this trigger them leaving?
Please let me know any thoughts!