One general conclusion of optimal foraging studies has been that animals seek to maximize their rate of energy intake . Indeed, floral features that influence the rate of energy intake of pollinators have been shown to affect patterns of flower visitation and specificity of pollinators [17,68-72]. Although the utility of energy intake rate has been called into question by some authors [73-76], apparent violations of this rule may result from a misunderstanding of an animal's "temporal scale of optimization" . For a nectarivorous animal, the rate of energy intake can be measured over the timescale of feeding, over a single flower visit, or over an entire foraging bout. In the following sections, we partition functional aspects of nectar feeding into several phases of a flower visit: proboscis extension, floral probing, fluid feeding, and proboscis retraction.
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