signs of swarming

what do folks look for to indicate that swarming is imminent in a colony?

if the hive in question has got a window, I look for bees sort of hanging around underneath the lowest combs. not like when they're chaining to build more, but more of a mass of bees where there wasn't one before.

I've also heard that the noise following a knock on the hive is substantially different just before swarming. more of a hiss, perhaps? hard to hear much of anything inside my hives made of thick wood, though.

new queen cups would be a pretty sure sign, but what about evidence that is observed outside the hive?

Tel wrote "...but what about evidence that is observed outside the hive?"

On the times I've been in the apiary when a swarm has issued there were what are sometimes called mass orientation flights, but which Tautz sees as flights preparatory to swarm issue. Bees are seen 'dancing' in a cloud in front of the hive about to swarm, facing the hive. If a swarm does not issue, the cloud melts away. The latter occurs within the space of up to about a quarter of a hour.

Another useful indicator is scouts appearing at batit hives within range of the apiary. The pre-swarm cluster, that Tel describes, can start looking for a new home before issue.

The pre-swarm cluster is also described by J-M Frèrés & J-C Guillaume in their book 'L' Apiculture Écologique de A à Z'. Their 'ecological hive' is a modification of the Warré, the change so far most attractive to beekeepers being a window in the back of each box. It is from these authors that the Warré with windows is derived. Presumably the reason pre-swarm clusters are not reported in frame hives is that the space is filled to the floor with wood and combs.