Fig. 7.2. A schematic of a test for cue preference. The plain feeder of the four feeders on the left contains food. The animal is allowed to eat some of the food. While the animal is absent from the feeder array, the plain feeder is emptied and switched with one of the other feeders. The order in which the animal visits feeders is then observed.
contains food that the animal is unable to finish in one visit. Having eaten some part of the food, the animal is removed and the rewarded feeder is exchanged with one of the other feeders (see Fig. 7.2). When the bird returns, all the feeders are empty and the order in which the bird visits the feeders is observed. Food-storing birds, which need to remember many locations to relocate caches, are more likely to visit the feeder in the (formerly) correct location. Non-storing species are as likely to visit the feeder in the correct location as the feeder with the correct color/pattern. Although this design does not test memory capabilities for the two different types of cues, it can tell us which cue type the birds prefer to remember, or attend to, when foraging at flowers. Our hummingbirds behaved as did the food-storing birds. We interpret these data as demonstrating that, for the hummingbirds, spatial information regarding the flowers on which they feed is more important than the flowers' visual aspects. Locations and spacing of flowers and plants may, therefore, play a much greater role in hummingbird/plant pollination relationships than has been considered previously.
In order to determine whether a rufous hummingbird can remember specific locations of flowers it had depleted, we employed an "open-field" version of the radial-arm maze (eight flowers presented in a circle), a standard laboratory apparatus used for testing spatial memory. In Phase 1, birds in the field were allowed to visit and deplete the rewards in four "arms" of the eight-armed maze (Healy & Hurly 1995). In "free" trials, this meant birds visiting four of eight possible rewarded flowers. The birds were scared away or left after feeding from these four flowers. In "forced" trials, only four rewarded flowers were provided. On returning to the maze after being kept away for at least 5 min, the bird was presented with
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