Memory for flowers in rufous hummingbirds: Location or local visual cues?

Rufous hummingbirds, Selasphorus rufus, remember locations of flowers. They avoid flowers they have emptied recently and those they have found to be empty. In contrast, after one brief experience they return to flowers they have left with food remaining. To determine whether hummingbirds primarily use spatial or colour/pattern cues to return to previously visited flowers, two field experiments were performed. In the first, subjects fed from a reward flower and on their subsequent return had to choose between visual cues that were dissociated from spatial cues. The birds showed a marked preference for returning to the correct location of the previously visited flower and not to the flower bearing the appropriate colour/pattern. The second experiment involved a delayed-matching-to-location task in which the subjects fed from, but did not deplete, a focal flower and on return had to choose between the focal flower and a new distractive flower. The latter was presented at three different distances from the focal flower and was either the same or different in colour to the focal flower. Subjects most often chose the focal flower when the distractive flower was of a different colour, whereas performance was poor when it resembled the focal flower. However, a significant interaction between the colour and distance of the distractive flower suggests that the hummingbirds were able to discriminate between focal and distractive flowers under both conditions, but that they employed different foraging tactics according to the colour of the distractive flower in the choice phase. (C) 1996 The Association for the Study of Animal Behaviour.