I've often commented, drift is more than simply to end of a row or in reference to a geographical landmark.  Those are factors.
However, 27 colonies, on-line, with highly accurate bi-directional bee counters mounted to the entrances, over 5 years, clearly showed that colonies have some form of colony specific 'drift' factor - the return rates at end of day follow a bell curve.  There are always ACCUMULATOR colonies that are not position-specific - these may occur anywhere in the apiary from edges to center and every place in between.  These colonies consistently have more bees returning than went out, day after day.  There are others that are DISPENSERS, these colonies consistently have fewer bees returning than went out, again, day after day.  Every colony in a beeyard has its own specific rate of return, that in the absence of some other factor, such as a pesticide drift/kill incident, is consistent.


My students also did two trials that the journals rejected, not due to the science, but because the reviewers said it was either a trivial issue or of no great interest to readers.  In one trial, the student made up packages of bees from a beekeeper whose colonies were derived from bees of a different source and genetic background than the bee colonies in an apiary set next to a paved highway.   He marked the package bees with color chalk, then dumped them at various distance along the highway, before and after the apiary location - e.g., 1/4 mlle, 1/2 mile, 1 miles from the test apiary.  Each distance and direction was marked with a different color.  Bees from all distance and locations eventually showed up in the apiary, and he has pictures of these marked bees freely entering colonies, with four of the chalk-marked bees showing up in the queen's court.  


In another trial, several students released color marked bees in four compass directions from an isolated apiary.  The bees released downwind showed up sooner, those upwind of the apiary took longer, but eventually, again, bees of all colors from all directions ended up in the test apiary and a couple of colonies had the highest numbers of these marked bees entering - colonies that were deep inside the grid of colonies, not on the edges, ends, or corners.  And the ACCUMULATOR colonies had immigration from all directions.


My point, which obviously I've not convinced people of - in addition to the known drift factors there's something innate to colonies that determine whether they tend to stay neutral or gain or lose forager bees.

l


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