Hummingbird foraging preferences under natural and experimental conditions

Background. Different studies have assessed hummingbirds’ preferences for feeding resources, mainly according to floral characteristics such as shape, color, and morphology, in addition to the nectar concentration, quantity, and sugar composition of flowers visited. Flower preferences can also depend on hummingbirds’ life history with respect to flower use. Hence, latitudinal migrant hummingbirds likely differ from resident species as they are accustomed to using a wider range of resources. In this study, we assessed the flower preferences of a migrant and a resident species that are common during winter in northern Mexico using both observational and experimental methods. Methods. We assessed hummingbird preferences for the most common plant species in the study region. In particular, we compared the preferences of two common hummingbird species, one resident (Amazilia beryllina) and one latitudinal migrant (Selasphorus rufus), for the most regionally common plant species, Cestrum thyrsoideum and Salvia iodantha, which have different color flowers yet produce similar energetic rewards. We calculated the Jacob selectivity index from preference data obtained under natural field conditions and with a flight cage in order to evaluate specific interactions. Results: Both hummingbird species showed different visitation rates to the studied plants under natural conditions in the study site. A. beryllina visited the yellow flowers of C. thyrsoideum more frequently, while S. rufus visited the fuchsia flowers of S. iodantha with greater frequency. In the flight cages, both species preferred the fuchsia flowers of S. iodantha when presented in similar or lesser abundance than the yellow flowers. Discussion. Under natural conditions, A. beryllina visited C. thyrsoideum to a greater extent in comparison with S. iodantha yet preferred S. iodantha in the flight cage when other hummingbirds were absent and even when S. iodantha was not the most abundant species. This could confirm that competition is an important process that drives the niche displacement of A. beryllina. On the other hand, the latitudinal migratory species S. rufus maintained its preferences for flowers of a familiar color under both natural and experimental conditions. Conclusions. Our results showed that the feeding preferences of the studied hummingbird species depend on the life history of each species. Therefore, the response of these migratory hummingbird species to feeding resources and possible exclusion from their preferred resources depends on their type of migration, territoriality, and possible associations with local plants.