Divergence in New Holland Honeyeaters (Phylidonyris novaehollandiae): Evidence from morphology and feeding behavior

Studies of island versus mainland populations have provided insights into processes that shape adaptive divergence (e. g., through selection in allopatric populations) as well as patterns of morphological change. In this study, we compare the morphology and foraging behavior in New Holland Honeyeaters (Phylidonyris novaehollandiae) between Kangaroo Island and the South Australian mainland. We (1) provide descriptive information on morphology traits across populations to test previously described differences; (2) test the prediction that island birds will have a wider foraging niche, different use of foraging substrate, and different foraging techniques, and (3) test for evidence of reduced prey diversity on islands as evidenced by longer foraging time. The results provide support for the predictions. Island birds were larger than the mainland birds in tarsus (2. 5%) and bill length (3. 7%), had a wider foraging niche (mostly due to greater insect consumption), and foraged more from the bark and air (sallying). Consistent with other studies of island biogeography, at least one common mainland predator and several bird species are absent from Kangaroo Island, which may facilitate niche expansion in the island birds. A wider niche could also be favored by lower prey diversity on islands (a depauperate community): in this study, island birds had longer foraging times than mainland birds, which may be evidence for lower total prey density.