Energetics of foraging and resource selection by honeyeaters in forest and woodland habitats of Western Australia

Abstract

Nectar is a major source of energy for most Western Australian honeyeaters. Its availability varies considerably within woodland and forest habitats, being influenced particularly by the distribution of nectar-producing plant species and their flowering phenologies. At any given time of year, overall nectar availability is greatest in regions where species whose flowers produce large quantities of nectar are most abundant. Nevertheless, asynchronous flowering by a variety of species generally ensures that some nectar is available in all regions throughout the year. Nectar availability varies from plant to plant within a species, usually being greatest for those plants that bear the most flowers. It also differs from one flower to another, generally being greatest in flowers that have been open for 1–2 days and which have not been subjected to intense foraging by honeyeaters or other nectarivores. Large and medium-sized honeyeaters forage preferentially at patches of vegetation that contain the greatest numbers of plants and which offer rich nectar rewards, although the patches and important plant species vary according to the time of year. These honeyeaters also forage preferentially at those plants that bear the greatest numbers of flowers at any given time, and at individual flowers that are most productive. Small honeyeaters may also forage selectively at times, although they are probably forced to utilise inferior nectar sources on many occasions when larger honeyeaters are present. By selecting particular flowers or patches of vegetation, honeyeaters are able to increase foraging profitability and reduce the number of flowers that must be visited in order to satisfy their total energy requirements. This is of particular benefit to large and medium-sized honeyeaters, allowing them to remain in areas after flower counts for the most productive species start to decrease. Nevertheless, a stage is ultimately reached when foraging by these birds becomes unprofitable and they vacate the areas. In forest and woodland habitats, nectar availability during summer is low and profitable foraging only possible for small honeyeaters.

Keywords:

• Energetics
• honeyeaters
• foraging
• nectar
• resource selection
• Western Australia