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.