The signals initiating the mass exodus of a honeybee swarm from its nest
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Animals that travel in groups must synchronize the timing of impending departures to ensure group cohesion. The mechanisms used by a honeybee, Apis mellifera, colony to organize the departure of a swarm from its nest remain a mystery. We examined the signals that trigger a swarm's explosive exodus from the parental nest, and we documented the concurrent changes in bee density and mobility. Using video recordings of swarms exiting observation hives, we analysed how bees in three swarming colonies prepared for and then performed their sudden departures. Over the 60 min before swarm exodus, the production of piping signals gradually increased and ultimately peaked at the start of the swarm departure. Also, during swarm exodus, bee density (number of bees in 100 cm2) dropped markedly, whereas the average bee velocity (mm/s), and the production of buzz-run signals, spiked dramatically. Neither waggle runs nor shaking signals showed increases before or during swarm exodus. The explosive departure of a honeybee swarm from its parental nest shows how animals can use the same communication signals in different contexts; we now know that honeybees use piping and buzz-run signals to initiate both a swarm's departure from its nest and a swarm's take-off from its bivouac site. This study also shows how a small minority of individuals in a social insect colony can operate as an oligarchy to make an important decision, i.e. when a swarm should leave its nest to found a new colony. 2008 The Association for the Study of Animal Behaviour.