Is the uncommon Black-chinned Honeyeater a more specialised forager than the co-occurring and common Fuscous Honeyeater?

In New South Wales (NSW), Australia, the Black-chinned Honeyeater ('Melithreptus gularis') is uncommon in comparison with the co-occurring Fuscous Honeyeater ('Lichenostomus fuscus'), which is common. The relative rarity of the former may be because it specialises on a narrow range of resources that are not abundant. Alternatively, it may be excluded from more abundant food resources by other bird species, such as the Fuscous Honeyeater. We thus compared the foraging ecologies of these two species on the New England Tableland of NSW. Broad-scale quantitative analysis of foraging, using tree species, foraging height, height of tree species, and conventional categories of foraging manoeuvres (glean, probe, snatch, hawk and pounce) revealed only slight differences between the foraging ecology of the two species. However, when foraging was investigated using finer scale analysis of gleaning techniques, Black-chinned Honeyeaters were found to spend a greater proportion of effort probing between leaves that were bound together than did Fuscous Honeyeaters. This supports the hypothesis that Black-chinned Honeyeaters are less common than Fuscous Honeyeaters because they are more specialised in foraging and their food supply is uncommon. Aggression did not seem to inhibit foraging for either species.