Honeyeater foraging: A test of optimal foraging theory

Honeyeaters (Meliphagidae) were observed foraging for nectar from Lambertia formosa inflorescences, each of which has seven flowers. The frequency distribution of numbers of flowers probed per visit to an inflorescence was found to be bimodal, with one peak at two and the other at seven. It is hypothesized that this frequency distribution results from a rule of departure from inflorescences that maximizes the net rate of energy gain. Patterns of nectar distribution were determined for a large sample of inflorescences. In addition the extent to which the honeyeaters re-probe flowers during a visit to an inflorescence was estimated. From these data and from field measurements of the times required by the honeyeaters to perform the various foraging behaviours, computer simulations of honeyeater foraging were constructed. These simulations led in turn to optimal frequency distributions of numbers of flowers probed per inflorescence that were bimodal but had peaks at 1 and 7 instead of 2 and 7. Although the observed and predicted behaviour were consequently similar, the difference between them was nevertheless significant. This difference could have been due to the birds' transient occupancy of the study area.