Floral resources and hummingbirds on an island of flooded forest in Central Brazil

Nectar availability for hummingbirds was studied for two and a half years in an island of flooded forest in Uberlândia, MG, in the Cerrado region, the Neotropical savanna areas in Central Brazil. Flowering individuals of ten plant species from eight families that offered resources potentially used by hummingbirds were recorded along transects crisscrossing the area, which were surveyed every other week. The number of flowers was estimated for each plant. The volume and concentration of nectar were measured for a sample of flowers of each species, and the data were used to estimate the caloric content available per flower and the general resource availability in the area throughout the study period. Focal observations of hummingbird visits were carried out on blooming individuals of all plant species. Hummingbird flowers occurred throughout the study period between January 2001 and June 2003. Only three of the studied plants did not present clear ornithophilous features. Six hummingbird species were recorded in the area, but total nectar availability in the area was seldom sufficient for the daily energy requirements of a single bird. Therefore, it can be inferred from the study that these hummingbirds need to move among the mosaic of different plant physiognomies in the region in order to obtain enough energy for their survival. These movements may also contribute to increasing gene flow and regeneration of plant populations isolated in forest patches as the one studied here.