The Effect of Artificial Feeders on the Spatial Distribution of Broad-tailed Hummingbirds

Abstract

Thousands of flowering plant species rely on hummingbird pollination. Artificial feeders represent an alternative, valuable food resource for hummingbirds, but little is known about the impact of feeders on hummingbird territory selection and territorial distributions. The field portion of this study examined the mechanisms of territory selection and the causes of territorial abandonment in a population of Broad-tailed Hummingbirds, Selasphorus platycercus. Territory selection was found to depend on the visibility of the territory for ease of defense and on food access, including feeders and flowers. Territorial abandonment was found to be due to the arrival of aggressive stopover hummingbirds and reductions in female receptivity to mating. These results from the field were used to make a game theory model predicting hummingbird investment across flower-dense areas and in proximity to feeders. Flower and feeder access were found to be alternative strategies, such that proximity to the feeder corresponded with lower flower density on territories. Simulations of territory distributions were constructed to assess how changes in the abundance and sugar content of feeders affect hummingbird territory distributions and pollination. A higher abundance of feeders was found to increase reductions in flower density on territories and likely in pollination. In contrast, reducing the sugar content in a feeder was found to greatly reduce its impact. The results of this study reveal the large effect of feeders both on individual hummingbird decision-making in territory selection and on hummingbird territory distributions; however, maintaining proper sugar concentrations in feeders greatly reduces their impact on hummingbirds and limits potential decreases in pollination.