Bumblebees utilize floral cues differently on vertically and horizontally arranged flowers

Pollinators have the capability of discriminating a wide variety of floral cues in order to identify rewarding flowers. However, little is known about how possible ecological or functional implications of horizontal and vertical positioning of flowers affect pollinator decision making. Flowers are commonly either arranged horizontally in meadows or vertically in inflorescences and blooming trees or bushes. Using bumblebees (Bombus terrestris), we here investigate if these 2 different foraging scenarios affect decision-making accuracy using an operant learning paradigm. Training foragers to feeders arranged either horizontally or vertically but bearing identical color or pattern cues, we found a highly significant and consistent difference in feeder choice accuracy. Bees presented with horizontally arranged feeders achieved accuracies of more than 90% by the end of the training. In contrast, bees foraging on vertically arranged feeders largely disregarded the feeder cues and accuracies remained well below 70%. Apart from feeder arrangement (horizontal, vertical) neither cue type (color, pattern), feeder display orientation (horizontal, vertical) nor vertical feeder distribution contributed significantly to choice accuracy. Training bees successively on vertical, horizontal, and vertical feeder arrays revealed that individual bees are capable of discriminating the presented feeder cues with high precision on the horizontal plane but did not use the acquired knowledge on subsequently presented vertically arranged feeders. Our results indicate that the spatial arrangement of flowers has marked effects on the foraging strategy employed by a generalist pollinator. We discuss the broader implications of foragers selectively allocating attention to focus on or disregard environmental information depending on spatial context.