Learning when to learn: hummingbirds adjust their exploration behaviour to match the value of information

Exploration is a key part of an animal’s ability to learn. The exploration-exploitation dilemma predicts that individuals should adjust their exploration behaviour according to changes in the value of information. Here, we test this prediction by tracking ruby-throated hummingbirds as they foraged repeatedly from a large array of artificial flowers, wherein 25% of the flowers contained a sucrose reward. Similar to real-world floral dynamics, the reward locations were consistent in the short-term, but varied from day to day. Thus, the value of information about the flower contents would be greatest at the beginning of a daily foraging session, and decay toward the end of each session. We tracked five individual hummingbirds in repeated foraging sessions, comprising more than 3,400 floral probes. We analyzed two metrics of their exploration behaviour: (1) the probability that a bird would shift from probing one flower to another, and (2) the Shannon information entropy of a sequence of flowers probed. We show that initially, the hummingbirds increased their exploration behaviour as time elapsed within a session. As they performed more sessions and learned the rules of the environment, the hummingbirds switched to explore more diverse choices at the beginning of a foraging session, when the value of information was high, and less diverse choices toward the end of a session. Our results suggest that foraging hummingbirds can learn when to learn, highlighting the importance of plasticity in exploration behaviour.