Hierarchical strategy for relocating food targets in flower bats: spatial memory versus cue-directed search

The search and orientation behaviours used during foraging depend both on a forager's perceptual and memory abilities and on the spatiotemporal pattern of food distribution. We examined whether nectar-feeding bats using spatially and temporally predictable resources can pinpoint known flower targets within patches from a spatial memory-based approach alone or whether only a coarse-grained spatial memory requires local search for the target's object features within patches. We developed echoacoustically distinct geometric objects as unique acoustic 'colour markers' on experimental flowers. We could show that regional scale geometry of the local target environment influences orientation during target approach. Target choice was dependent on the relative positional information of local spatial cues when they were within a 20-cm radius around the target. For a dissociation experiment we first conditioned bats (in the laboratory and the Costa Rica rainforest) to a single target within an array of echoacoustically distinct feeders. During tests feeders were shifted and object cues rearranged. Bats directed initial choices most often at the feeder at the same absolute spatial coordinates as during the learning phase but later choices at the previously rewarded floral object cue. Thus bats had remembered both spatial and object attributes of their food target. However, their search strategy was to rely primarily on spatial memory and only secondarily on cue-based search. Flight approaches to feeders that were guided primarily by spatial memory were of significantly shorter duration than approaches that included active object-cue identification. This indicates a short-term energy advantage of the spatial memory-reliant strategy.