http://www.ars.usda.gov/research/publications/publications.htm?
SEQ_NO_115=155925

<<We examined nest usurpation (colony takeover) by African honey bee
swarms over a two-year period in an apiary that contained 76 European
colonies maintained in Tucson, AZ. We observed a mean annual usurpation
rate of 21%, with highest usurpation rates occurring from October-
December.>>

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