> I would like to see the evidence that leads one to assume bees “tend to
> separate their colonies by about half a mile”.  I would think that this is
> within the chance of random for feral colonies to appear to be spread out
> by that distance.

Exactly.  I don' t think the bees do this deliberately.  I suspect it is a 
result of the climate, terrain, flora, and also the health and swarming 
tendancy of the bees in question.

> There are many references that dispute this assumption

There are many factors which can be expected to cause exceptions, one way 
and another.  It may be a useless generalization. 

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