Foraging theory assumes that animals assess value based on objective payoffs; however, animals often evaluate rewards comparatively, forming expectations based on recent experience. This form of evaluation may be particularly relevant for nectar foragers such as bumblebees, where individuals can visit thousands of flowers daily that vary in nectar quality. While many animals, including bees, demonstrate reference-based evaluation in experimental contexts, it is unclear whether this occurs in the wild. Here, we asked how daily experience with wildflower nectar influenced wild bumblebees’ reward evaluation. We measured the daily nectar concentration of bee-visited wildflowers (Penstemon spp.), before presenting foragers with conspecific flowers filled with a range of artificial nectar concentrations. We recorded bees’ acceptance of artificial nectar, the probability of subsequent visits to flowers on the same plant, and residence time. While bees had a minimum threshold of nectar acceptability that was unaffected by experience, when there was higher-concentration environmental nectar, they were less likely to accept lower-quality rewards on manipulated plants. Bees also visited more flowers and stayed longer on plants with higher-concentration nectar. This study shows evidence for both absolute and reference-based evaluation in wild bees and points towards differences between bees’ behavior in lab- and wild-foraging contexts.

中文翻译：

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野生大黄蜂在觅食时同时使用绝对和相对评估

觅食理论假设动物根据客观回报评估价值；然而，动物经常比较地评估奖励，根据最近的经验形成期望。这种形式的评估可能与大黄蜂等花蜜采集者特别相关，因为大黄蜂每天可以访问数千朵花蜜质量各不相同的花朵。虽然包括蜜蜂在内的许多动物在实验环境中表现出基于参考的评估，但尚不清楚这种情况是否发生在野外。在这里，我们询问了日常野花花蜜的经历如何影响野生大黄蜂的奖励评估。我们测量了蜜蜂访问过的野花（Penstemon spp.）的每日花蜜浓度，然后向采集者提供充满了一系列人工花蜜浓度的同种花。我们记录了蜜蜂对人工花蜜的接受程度、随后访问同一株植物上的花朵的概率以及停留时间。虽然蜜蜂对花蜜的接受程度有一个不受经验影响的最低阈值，但当环境花蜜浓度较高时，它们不太可能接受受操纵的植物的较低质量的奖励。蜜蜂还会拜访更多的花朵，并在花蜜浓度更高的植物上停留更长时间。这项研究为野生蜜蜂的绝对评估和基于参考的评估提供了证据，并指出了实验室和野生觅食环境中蜜蜂行为的差异。