Aggression and Nectar Use in Territorial Non-Breeding New Holland Honeyeaters Phylidonyris novaehollandiae in Eastern Australia

Abstract

Territorial non-breeding New Holland Honeyeaters Phylidonyris novaehollandiae were studied in an open forest in eastern Australia. During winter, birds maintained priority of access to nectar from Banksia inflorescences but the extent to which this use was exclusive was variable. I examined the aggressive responses of these birds to intruders of different sizes (interference behaviour), and their use of defended nectar (exploitation behaviour). Owners displayed interspecific discrimination with all honeyeater species being excluded except the much larger wattlebird which was harassed while feeding. Owners expelled a greater proportion of intruding conspecifics compared to other species and used more aggressive behaviour (chases) against them. Energy inexpensive aggression (displacements) was used against smaller intruder species who were also more likely to be attacked if they attempted to feed. The rate at which intruding honeyeaters were expelled (birds/h/m²) increased with both nectar abundance and intruder pressure but actual territory exclusiveness (proportion of intruders expelled) was highest only at moderate nectar levels (lower when nectar was poor or very rich). Owners visited inflorescences in their territories more often than intruding honeyeaters, and fed at the most productive inflorescence stages. Nectar within territories was depleted at a faster rate then undefended nectar. Consequently, the territories appeared to be operated as nectar 'sinks', rather than as the 'sources' typical of other nectarivorous birds.