Nectar-feeding animals have served as the subjects of many experimental studies and theoretical models of foraging. Their willingness to visit artificial feeders renders many species amenable to controlled experiments using mechanical “flowers” that replenish nectar automatically. However, the structural complexity of such feeders and the lack of a device for tracking the movements of multiple individuals have limited our ability to ask some specific questions related to natural foraging contexts, especially in competitive situations. To overcome such difficulties, we developed an experimental system for producing computer records of multiple foragers harvesting from simple artificial flowers with known rates of nectar secretion, using radio frequency identification (RFID) tags to identify individual animals. By using infrared detectors (light-emitting diodes and phototransistors) to activate the RFID readers momentarily when needed, our system prevents the RFID chips from heating up and disturbing the foraging behavior of focal animals. To demonstrate these advantages, we performed a preliminary experiment with a captive colony of bumble bees, Bombus impatiens. In the experiment, two bees were tagged with RFID chips (2.5 × 2.5 mm, manufactured by Hitachi-Maxell, Ltd., Tokyo, Japan) and allowed to forage on 16 artificial flowers arranged in a big flight cage. Using the resulting data set, we present details of how the bees increased their travel speed between flowers, while decreasing the average nectar crop per flower, as they gained experience. Our system provides a powerful tool to track the movement patterns, reward history, and long-term foraging performance of individual foragers at large spatial scales.
Artificial flowers BombusForaging LED sensors Renewing resources RFIDs Spatial use
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Chad Brassil first suggested the use of radio-tagging technology for tracking and identification of bees. Alex Fujiwara and Toshiyuki Kaneko (Hitachi-Maxell Corporation) provided the product specifications of the Coil-on-Chip RFID system® required for developing the data acquisition system. Alison Leslie helped us improve the design of flowers and perform data collection. Luu Trung crafted the artificial flowers. Useful discussion and invaluable help have been contributed by James Burns. Jonathan Cnaani, Robert Gegear, and Michael Otterstatter also contributed to the development of our idea. Biobest provided a commercial colony of B. impatiens. Two anonymous reviewers made useful comments on the manuscript. This research was supported by a fellowship of the Japan Society for the Promotion of Science for Research Abroad and Grant-in-Aid for Young Scientists (B) to K.O. and grants from the Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation, and the Ontario Innovation Trust to J.D.T.
Contributions of authors
J.D.T. conceived and designed the original motorized artificial flowers for continuous nectar secretion. K.O. refined the mechanical aspects of artificial flowers so that a bee can obtain only a small amount of nectar at once. D.D., K.O., and J.D.T. devised the monitor system. D.D. built the monitor system, including both instrumentation and software. K.O. and J.D.T. planned and performed the preliminary experiments. All authors read and approved the final manuscript.
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