OVERNIGHT MEMORY RETENTION OF FORAGING SKILLS BY BUMBLEBEES IS IMPERFECT

Newly emerged bees learn to forage more efficiently as they gain exper ience. To test the hypothesis that foraging efficiency would increase as bees gain experience during the day, but would decrease after a nig ht, owing to loss of memory, naive Bombus terrestris bumblebees were a llowed to forage on two clusters of artificial flowers of unequal prof itabilities during 3 consecutive days. Nectar intake rate, percentage of visits to the more profitable cluster, probing time and time interv als between visits were computed as measures of the bees' foraging eff iciency. Nectar intake rates increased significantly during the day, a nd decreased partially but significantly after a night. They varied gr eatly between bees. The bees did not show a preference for one of the clusters at the onset of the experiment, and none consistently increas ed their visits to the more profitable cluster during single observati on days. Most individuals did not visit the higher-reward cluster excl usively by the end of the third day. However, visits to the higher-rew ard cluster did increase significantly when the first day of observati on was compared with the third day. Preference for the higher-reward d uster increased after the first night but decreased significantly afte r the second night. Probing time and inter-visit intervals decreased s ignificantly during observation days, and increased significantly afte r a night. The results indicate that bees learn to approach and probe flowers faster, as they gain experience, during a foraging day, but th at these skins are partially forgotten overnight. Patch preference is formed more slowly. Once formed, it is also weakened overnight. Such p artial forgetting may aid the bee in reacting quickly to overnight cha nges in resource profitability by modifying flower choices and handlin g techniques. (C) 1996 The Association for the Study of Animal Behavio ur.