Cartar (1992a) and Dukas & Visscher (1994) found that efficiency increases over roughly the first week of a bee's foraging career (an effect which can likely be attributed to learning what, where, and how to forage, and more complex foraging rules). Dukas & Visscher also observed that foraging efficiency declines later in life, but this effect need not necessarily be related to an age-related decline in cognitive ability. In fact, controlled studies show no effects of age on learning ability in honeybees (Bhagavan et al. 1994) or bumble bees (Chittka & Reinhold 1999). Several factors affecting foraging efficiency are potentially correlated with age of foragers, for example parasite load (Schmid-Hempel & Stauffer 1998) or wing wear (Cartar 1992b). Having seen several marked bumble bees die during foraging bouts, one of us (JT) can state with certainty that they slow down greatly as their time runs out. In honeybees, a decline in foraging efficiency with age might also be explained by assuming that seasoned foragers invest more time into scouting for new food sources than into harvesting.
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