Elements of episodic-like memory in free-living hummingbirds, energetic consequences

Episodic memory has been described as the ability to recall personal past events, involving what, where and when an event has been experienced. Cognitive abilities like learning and memory are pivotal to the performance of many behavioural traits such as food procurement. Nectar, the primary food of hummingbirds, is dispersed in hundreds of flowers and varies in concentration and renewal rate. Therefore, a hummingbird that can remember elements of episodic-like memory such as what, where and when the nectar becomes available will have a higher energy rate of intake when compared to random foraging. We conducted a field experiment with green-backed firecrown hummingbirds, Sephanoides sephaniodes. We assessed the ability to recall the location, nectar quality and renewal rate of the most rewarding flowers among several less rewarding flowers with identical visual cues. Hummingbirds were able to remember the most profitable nectar sources and flower position and adjust their visits to nectar renewal interval. Cognitive performance varied among individuals, implying up to 6.3-fold differences in energy gain. Our results strongly suggest that hummingbirds use cognitive abilities to exploit nectar sources efficiently and, therefore, that cognitive abilities are potentially tied to survival probability.