I am very interested to hear this as just to day I had an exact experience.
This morning visually checked the hive as I do most mornings. Returned mid morning to find a large cloud of bees and a swarm in a dwarf apple tree some 25ft from the main hive, they were at head height.
Wow thinks I! my first real swarm to collect. Having all the equipment to hand as its in my garden I swing into action.
Collected swarm by dropping them into a plastic tub and then drop them into the hive, replace frames of foundation. Close up and feel very smug.
Mate turns up and we chat. 1.1/2 hrs later bees are airborne in increasing numbers.
Clearly not so cleaver after all! but notice that the hive behind the garage has a large cloud of bees around it. On investigation the bees are clustering on the front and clearly moving into the hive, I did examine their activity and there did not seem to be any fighting.
Set up spare hive next to main and left them to it, guess there going to do what there going to do!
Got the books out as it did not seem to make any sense.
Whole time line was 10.30am found swarm within hr the swarm was in new hive every thing settled down by 12 ish bees on the wing and by 1.30 all quiet and their back in the main hive, been keeping an eye on them off and on all afternoon and the hive is quite happy by their activity via the front door.
Original cluster was approx 4ltr by volume excludes the bees on the wing.
When I first found them there were quite a number of birds clearly having a feeding fest.
My thinking was a possible matting flight but I have no knowledge of how many bees would accompany the queen on one.
Or loss of queen as has been suggested. The hive is quite settled and activity seems normal they are un aggressive, they had been a bit tetchy this last 2 inspections which I had put down to less than ideal weather conditions etc.
Like Beeconcerned any suggestions on a course of action, or what to look out for would be welcomed. None of the books I have seem to cover this situation.
Regards philip