Banksia nectar and pollen: Dietary items affecting the abundance of the common blossom bat,Syconycteris australis,in southeastern Australia

Abstract The relationship between the abundance of the common blossom bat (Syconycteris australis), a nectar/pollen specialist, and the availability of its food sources was investigated across nine Banksia integrifolia heathland sites in coastal New South Wales, Australia. An index of bat abundance was more highly correlated with direct estimates of food density (productive inflorescences) than indirect estimates of food (Banksia trees and total inflorescences). Furthermore, standing crops of nectar-energy per hectare were better predictors of bat abundance than pollen-nitrogen per hectare. Adult male mass did not differ significantly across sites of differing food availability, suggesting that the corresponding increase in bat abundance with food reduces the amount of fat an individual can deposit. Although males and females responded similarly to food, adult numbers were more strongly correlated with food supply and they were more likely to be recaptured than juveniles. Energy requirements of blossom bats exceeded availability in four out of nine sites. Flying foxes were heard feeding in large numbers at the remaining five sites, where energy was superabundant for S. australis. In contrast to the conclusions of previous studies of megabats, these results provide the basis for a prediction that nectar-energy, rather than pollen-nitrogen, is the primary limiting factor for populations of the blossom bat.