Hummingbird color preference within a natural hybrid population of Mimulus aurantiacus (Phrymaceae)

Hummingbird flowers are typically red in color but the reasons for this are not well understood. Relatively few studies have examined hummingbird flower color preferences under natural conditions in which flower color varies within a species. We recorded hummingbird visitation rates to flowers that vary in color from yellow to red in a natural hybrid population between red- and yellow-flowered Mimulus aurantiacus subspecies. We also examined whether there were any correlations between color and flower size or nectar content. Finally, we reviewed the literature on hummingbird color choice tests using feeders and flowers. There were no correlations in this population between flower color and flower size, nectar volume, or sugar concentration. Nevertheless, hummingbirds undervisited the two most yellow color classes, overvisited orange flowers, and visited the two most red color classes in proportion to their frequency in the population. While Hummingbirds preferred flowers expressing red pigments to those that did not, the flowers with the most red hue were not the most attractive, as has been observed in similar studies with other species of Mimulus. While feeder studies generally fail to show hummingbird preference for red, all studies using flowers, including those that control all floral traits other than color, find consistent preference for red. Experiments are suggested that might help disentangle hypotheses for why hummingbirds exhibit this preference.