Hello Chris,
Usually we do not speak on the subject around newbees because for the most 
part these type events are rare. Mainly rare because professional beekeepers 
sense when the bees are getting upset.

However many times we handle bees in poor weather when hives are at peak 
populations. Temps above a 100F. Even with smoke the bees are severely 
crowed in hives. A friend said when he loaded a semi of bees in Carthage. 
Texas last week the bees had poured from the hives under the netting so much 
it was hard to see the hives. However once on the road the bees moved in 
hives and arrived safely.

> Is this because of poor stock selection; rough handling; overcrowded 
> sites;
> robbing; inexperienced helpers, hive design or some other cause?

My opinion ( and many others may be of a different opinion)

In my bees most  is caused by working bees in poor weather conditions when 
no flowers are blooming ( most bees in the hives). We have had rain this 
spring 3-4 times a week and inches at a time. We four wheel drive in ( my 
helps head has hit the truck roof a couple times and mud is deep enough that 
at times your boot pulls off in mud) At the truckstop people walkover to 
check out the mud on the truck. At times we have to wipe the mud from the 
windshield before hitting the highway. The guy at the carwash hates to see 
me pull in.
This year we have been constantly in the hives making splits. Pumping feed 
and feeding patties. Went to the plant in Kansas for feed yesterday.  Some 
of my production donor hives have given up up to five splits this spring. 
The March splits are ready to super. Sub soil moisture and the high price of 
honey makes me put extra hives on the ground for honey production.
We are running a high number of hives in singles which creates more work for 
us such as swarming and second boxes and feeding after supers come off.
Some commercial beekeepers would not attempt the juggling act involved with 
my methods. One mistake and a whole yard of hives will hit the trees. Pull 
supers off single hives after the main honey flow and not put on second 
boxes ( room inside the hive for bees ) and feed and the hives will swarm or 
starve in Missouri in certain years in August ( period between summer and 
fall flows)
No two years are exactly alike so changes in mangagement are always subject 
to change. Honey flow dates from the year before mean absolutely nothing. 
Can sway two weeks in either direction. This time of year I cruise the bee 
location sites every couple days. You can not make good management decisions 
from an office chair!  last years best locations could be the worst this 
year. Next week I will be moving locations which lack the best sweet clover 
to areas with better sweet clover. I do not need to see the bloom to tell 
the best areas. The better method is to fly over the area when bloom starts.

I do not know which beekeeper said this quote:
" Even a below average beekeeper can make a living from bees with good 
locations and the best beekeeper can go bankrupt with only poor locations"

It has been a few years since I quoted from my friend Douglass Whynotts book 
"Following the Bloom"
"Across America with the Migratory Beekeepers" page 206 ( last page)

" As for me now I keep one hive. "
"I like to watch them, most of all, when I see them making their sweeping 
arcs, when they glide down among the crowds of bees at the entrance,I just 
watch. "

"Contraction has followed expansion, and I sometimes think of the Zen saying 
;

"At first the mountains were mountains, and then the mountains were not 
mountains,

but some other thing

 now the mountains are mountains again."

Happy beekeeping!

bob 

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