The association between nectar availability and nectarivore density in urban and natural environments

Abstract

In some Australian and South American cities, nectarivorous birds have become a conspicuous component of the avifaunal community. One mechanism that has been proposed to explain their success is an increased availability of nectar that is provided by suburban gardens and other ornamental plantings. To determine whether the amount of nectar within the suburban landscape is comparable to that of the natural environment, we measured floral density and nectar concentrations in 24 sites in Sydney, Australia. We also measured the density of four species of nectarivores and available nectar energy over a period of 18 months within the suburban landscape (streetscapes and remnant vegetation) and the natural environment (forest and heathland) to determine whether nectar availability explains nectarivore density. Two species of nectarivorous parrot, the rainbow lorikeet and musk lorikeet were present in higher densities within the suburban landscapes compared to the natural environment, and the suburban landscapes provided significantly more nectar than the natural environment during spring and winter. Both the rainbow lorikeet and musk lorikeet were associated with flowering of Eucalyptus spp. and red wattlebirds with the flowering of Grevillea and Callistemon spp. within streetscapes. Suburban landscapes appear to provide a constant supply of nectar for large-bodied nectarivores and provide for more efficient foraging, explaining the success of these species in urban environments.