Extrafloral Nectaries and Pollination of Acacia pycnantha Benth by Birds

Abstract

Acacia pycnantha secreted extrafloral nectar during winter. This coincided with flowering and not with herbivore damage to phyllodes. Phyllodes with axillary racemes or phyllodes towards the tips of branches were more likely to have nectar secretions than phyllodes without axillary racemes or away from the tips of branches. Although most phyllodes were damaged by herbivores to some extent, this damage had occurred prior to the secretion of extrafloral nectar in winter. Further damage to phyllodes was negligible during winter.

A variety of birds, including silvereyes and several species of honeyeaters and thornbills, consumed extrafloral nectar and in the process brushed against inflorescences. The activity of these birds in Acacia pycnantha, relative to their use of other plants, increased during the period of nectar secretion. When birds were excluded from flowering branches by mesh, pod production was significantly reduced. Natural rates of pod production were low and variable. These observations and results strengthen the role of birds as pollinators of Acacia pycnantha and we argue that these extrafloral secretions aid pollination and not reduction in herbivore damage in Acacia pycnantha.