Rufous hummingbirds' memory for flower location

We used an open-field analogue of the eight-arm radial maze to investigate the role of memory during foraging by rufous hummingbirds, Selasphorus rufus. In experiment 1 we attempted to determine whether birds were able to differentiate between flowers of the same type that they had emptied, flowers they had seen but not visited and new flowers. They were tested with three trial types, all of which involved birds visiting four rewarded flowers in the first phase of a trial. In 'free' trials, the bird was allowed to choose four from eight flowers. In 'forced' trials there were only four flowers available in phase 1 and in 'mixed' trials the bird could choose four from six available flowers. In all trial types eight flowers (including all those in the same locations as in phase 1) were presented to the bird on its return in phase 2. The four rewarded flowers were those not visited in phase 1. In free and mixed trials, birds were better than chance at avoiding the flowers they had emptied in phase 1. In mixed trials, birds were more likely to visit the new flowers that were unique to phase 2. In experiment 2 we tested whether flower height was a floral feature remembered by birds. Birds were given forced and free trials in which the flowers in the radial maze were presented at two heights. As performance in both trial types was better than chance we suggest that hummingbirds use flower height to remember the locations of flowers. (C) 2001 The Association for the Study of Animal Behaviour.