Drifting obviously occurs if the hives are all oriented in the same  
direction, in lines, with little marking, and is especially bad if a cross wind  tends 
to blow acoss the hives.  The end boxes will increase in  numbers.
 
That's the traditional description of drifting. Some years ago, we fitted a  
colonies with bi-directional counters and found another form of  'drifting'.  
It also occurred when abandoned bees (such as would blow off a  semi going 
down a highway) found new homes in a nearby apiary.

Within any beeyard are colonies that attract bees other than their  own.  
They can be ANY place within the yard.  Each day they have a  higher number of 
bees coming into the hive than left (percent return rate is  1-5% higher than 
for their neighbors.
 
In the same yard, some other colonies regularly lose a small percentage of  
bees each day, compared to their neighbors.
 
When we released marked bees in 4 compass directions from the center of a  
test beeyard (the released bees came from another bee operation miles away), we  
found that many of these bees, from all 4 directions, found the apiary, and 
most  of these bees went to the same colonies - which were often deep in the 
yard, Not  on the margins.
 
Whether this is 'drift' in the normal sense is a semantics question.   But it 
does happen, and most beekeepers are unaware of it - except for the  
observation that in any beeyard there are always a few super achieving colonies  and a 
few laggards.  From our counter data, the over achievers collect bees  from 
their neighbors.  The others lose bees each day, presumably to the the  better 
colonies.
 
Jerry



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