Risk taking decisions related to the unpredictability of resource availability (risk‐sensitive foraging theory) have typically been explained by behavioral ecology and psychology approaches. However, little attention has been given to the physiological condition of animals as a factor that can influence the direction of foraging preferences. We evaluated the role of steroid hormones testosterone (T) and corticosterone (CORT) on the foraging preferences expressed by white‐eared hummingbirds Hylocharis leucotis in a risk‐sensitivity experiment. We recorded choices made by male individuals to floral arrays with constant and variable rewards (sugar concentration), and associated these with steroid hormone levels quantified at the start of the experiments. We found that males with higher T levels behave as risk‐prone foragers as they perform more visits to flower arrays with variable rewards. Interestingly, CORT levels were similar regardless whether individuals visited both types of array. According to our results, T seems to influence the foraging preferences of male hummingbirds. Individuals with higher levels of this hormone, made more rapid, frequent visits to flowers with variable rewards, and behave consistently as risk‐prone foragers, compared to males with low T levels. These are exciting avenues for future work, particularly considering recent evidence that individuals may exhibit behavioral differences, denoting an apparent personality, which may be associated with phisiological condition influencing how they respond behaviorally to environmental variation.
Variations in the quality or quantity of a food source determines if an animal takes the risk of spending energy searching for or eating it. Hummingbirds have been traditionally catalogued as risk-averse foragers. However, the inclusion of more than 2 options in a foraging set for risk-sensitive experiments has resulted in the observation that some hummingbird species preferred intermediate risk even if they had been risk-averse in a traditional binary risk experiment. These contrasting results suggest an effect of having multiple foraging options that had been ignored due to the design of previous risk experiments. Here, we studied the influence of varying reward volume (Experiment 1) or sugar concentration (Experiment 2) on choice behavior of white-eared hummingbirds, Hylocharis leucotis, by recording their visits to feed from a sucrose solution located in 4 artificial floral arrays associated with constant, low, medium, and high variance. In both experiments, each of the vertical arrays was evaluated in a training stage and a test stage. The birds visited all the arrays without discriminating among them, and thus were indifferent to variations in the volume or sugar concentration of reward. Thus, there was no influence of variance of nectar volume and sugar concentration on the choice behavior of the birds, ruling out the possibility that white-eared hummingbirds are risk sensitive under these conditions of 4 foraging alternatives.
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