Well, build-up is going strong, so I've been raising queens and splitting. Last night I was rounding up empty, idle combs that still need trimming of End Bars to 1-1/4" width, and Top Bars to 7/8" width. While doing this I used my red LED headlight, so not to overly disturb colonies I was sorting through.
I discovered a surprise; one nuc, which was even one that was established in 2013, and had been going strong -- was entirely empty of bees, not a single adult bee was in the nuc, not even any dead ones, but four of their five combs were 1/3 full of capped worker brood (this brood nest was centered in the rear 1/3 of the four brood containing combs), with a rim of younger brood, then pollen/nectar. Some of the larvae had begun crawling from their cells, I attribute this to their not being fed, properly.
In an attempt to rescue any of this brood that hadn't yet starved or been chilled, I placed them above the brood nest of an adjacent strong nuc. Once any surviving capped brood begins emerging, I can consider using it for a replacement split.
The only other time I remember seeing brood abandoned like this, was when all my colonies were likely AHB, and I tried making a split, the split with the queen, absconded leaving brood and stores behind. They didn't return to the parent location, but left the vicinity of the apiary, never to be seen again. In that case, too, there weren't even any stragglers left to tend the brood.
Has anyone else seen such behavior?