Bees splitting their own brood ( sort of)

[SDM]

I had to unite 2 nucs a few weeks ago after a queen turned DL. Their late September mated queen was in overdrive and soon had 7 full frames of brood so they're staying in a double nuc for the winter. On the last inspection I noted that one side of a frame in the middle of the brood patch has no brood at all , but instead was completely filled with pollen.
I know its a big no no for us to split the brood , but have others noticed their own bees doing it in this way ?

[Duncan]

Yes, normal behaviour when the colony is reducing the size of the brood area. We see this usually at the end of August when the laying rate is reducing, they create this barrier and then fill the unused part with pollen and honey. We usually take the opportunity to remove 2 to 4 frames for extraction and replace these with new/reconditioned frames and foundation in October when brood rearing starts increasing again.

[SDM]

1 Colony was broodless and the other just 2 frames of brood when I united. The queen moved quickly into the top box and laid 3 frames then when she started laying in the lower one again she did it on the other side of the pollen frame. They were growing rapidly at the time, not shrinking.

[Duncan]

Obviously a bit ahead of the expansion and preparing for the end of the season.