Do sunbirds use taste to decide how much to drink?

Abstract

Nectarivorous birds typically consume smaller meals of more concentrated than of less concentrated sugar solutions. It is not clear, however, whether they use taste to decide how much to consume or whether they base this decision on post-ingestive feedback. Taste, a cue to nectar concentration, is available to nectarivores during ingestion whereas post-ingestive information about resource quality becomes available only after a meal. When conditions are variable, we would expect nectarivorous birds to base their decisions on how much to consume on taste, as post-ingestive feedback from previous meals would not be a reliable cue to current resource quality. Here, we tested whether white-bellied sunbirds (Cinnyris talatala), foraging from an array of artificial flowers, use taste to decide how much to consume per meal when nectar concentration is highly variable: they did not. Instead, how much they chose to consume per meal appeared to depend on the energy intake at the previous meal, that is how hungry they were. Our birds did, however, appear to use taste to decide how much to consume per flower visited within a meal. Unexpectedly, some individuals preferred to consume more from flowers with lower concentration rewards and some preferred to do the opposite. We draw attention to the fact that many studies perhaps misleadingly claim that birds use sweet taste to inform their foraging decisions, as they analyse mean data for multiple meals over which post-ingestive feedback will have become available rather than data for individual meals when only sensory information is available. We discuss how conflicting foraging rules could explain why sunbirds do not use sweet taste to inform their meal size decisions.