House-hunting by honey bee swarms: collective decisions and individual behaviors

Thousands of individuals in a house-hunting honey bee swarm make a collecti ve: decision for one among many nest sites discovered. Mie recorded the dan ces on swarms in a forested area, where one swarm's search encompassed abou t 150 km(2) and many different sites. We then analyzed swarms in a desert a rea with only nest sites that we provided and monitored, to study how the s warm winnows multiple finds to a single site over the course of a few days, Most bees did not visit any site, very few visited more than one. Apparent ly choices were made with little or no direct comparison, through the inter action of two mechanisms: positive feedback through recruitment leading to growth in the number of scouts visiting good nest sites, and attrition redu cing activity and recruitment for non-chosen sites. Individual differences between bees substantially affected these dynamics. Scouts varied considera bly in amount of dancing and persistence, but most that danced did so vigor ously after their first few visits, and then dropped out, ceasing their dan cing though continuing to visit the nest site. Dances were nearly twice as long as reported for nectar and pollen. Scouts followed dances of others, a nd occasionally visited alternative sites, but rarely switched their dancin g. When unanimity is reached the bees must recognize that a decision has be en made, break up the swarm cluster, and fly to the nest site. Buzz-running (Schwirrlaufen) probably plays a role here, but we observed less buzz-runn ing than previously reported, and this occurred even early in the process; it might function as a chain-reaction effect triggering the end of the hous e-hunting process. Our results suggest that the choice among nest sites rel ies less on direct comparison of nest sites, and more on inherent processes of positive feedback and attrition by dancers dropping out.