Fig. 7.6.(a) Experimental array of flowers in which the solid circles represent the array during training trials in which only the center flower was rewarded, and all others contained water. Spacing between flowers was 5, 10, 20, 40, 80, 160, and 320 cm. Open squares represent the locations of flowers during a test trial in which the array was shifted one spacing unit to the east.
on the more complex arrays after 40 trials. Therefore, they were still learning reward locations, but at a much slower rate (see Fig. 7.5b). In a second experiment, birds were trained on a quarters pattern for 30 trials, then presented with 30 trials of the mirror-image of the same pattern. All birds had been performing at 75% or more and all dropped to below 50% for at least two trials after the switch (see Fig. 7.5c). Sutherland & Gass (1995) interpreted these data as evidence that the birds knew which were the profitable locations rather than that they were using movement rules to decide which were good or bad feeders.
We carried out several field experiments similar to this latter one of Sutherland & Gass (Healy & Hurly 1998). In the first, we presented the birds (male rufous hummingbirds) with five feeders arranged in a cross with the middle feeder containing the reward (see Fig. 7.6a). The flowers were equally spaced at 5,10,20,40,80,160 or 320 cm. Once the bird had learned to visit only the central flower, the array was shifted one spacing unit in one of the four major compass directions. When the distances between flowers were 40 cm or less, the birds returned to the central flower, but when they were greater than 40 cm, the birds visited the flower in the previously correct location, as specified by larger landmarks surrounding the array (Fig. 7.6b). In a second experiment, we used an array of 16 flowers in a quarters design with flowers either 10 or 80 cm apart, all the same color or all bearing unique color patterns. Once the birds had learned the location of the rewarded flowers, we shifted the array as in the previous experiment. Color pattern affected how quickly
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