“Radiating despite a lack of character: ecological divergence among closely related, morphologically similar honeyeaters (Aves: Meliphagidae) co-occurring in arid Australian environments”

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Eliot T. Miller, Sarah K. Wagner, Luke J. Harmon, and Robert E. Ricklefs

Closely related honeyeaters have diverged in ecology despite conserved morphology

In this photo, Sarah Wagner is crouched observing and recording foraging honeyeaters in the monsoon forests of northern Australia. Eliot Miller captured the image in the field while the two of them were collecting the quantitative foraging measurements that enabled the researchers' investigation of niche partitioning in these species.
(Credit: Eliot T. Miller)

Usually a bird’s beak offers clues to the type of food it eats. A hummingbird’s long, slender beak is perfect for sipping nectar. The crossbill uses its unique bill to extricate pinecone seeds. But sometimes, appearances can be deceiving, according to research on Australian honeyeaters appearing in The American Naturalist.

Cornell Lab of Ornithology researchers Eliot Miller and Sarah Wagner crisscrossed the Australian continent to compare the diet, foraging behavior, and bill shape of the 75 species of honeyeaters that live there. Like hummingbirds, many honeyeaters take nectar, but some species also take insects and fruit. Their beaks generally reflect these species-specific dietary differences.

Though honeyeaters originally occupied Australian rainforests millions of years ago, that habitat is now found only in a slim margin along the coast. As a result, almost half of the species of modern honeyeaters live in the desert, which now makes up a significant portion of the continent—over 50% of the landmass receives less than a foot of rain per year.

“By and large, honeyeaters that live in the desert resemble their forest relatives in diet and foraging behavior. There are leaf-gleaning insect-eaters, nectar feeders, and those that feast on fruit. There is even a group of species that forages on bare ground like a little inland sandpiper. But morphologically, these species are only a subset of the diversity found in forests. These desert honeyeater species are using their ancestral morphologies in very different ways to survive.”

A photograph of one of Eliot Miller and Sarah Wagner's campsites, forty kilometers north of Broken Hill, New South Wales, Australia. This was one of the few areas the team found good numbers of pied honeyeaters (Certhionyx variegatus). They spent a day and a half here studying their foraging behavior before driving further inland.
(Credit: Eliot T. Miller)

For example, for a recent lecture, Miller stitched together a photograph of a Gibberbird and a photograph of a Green-backed Honeyeater into a single image of what appeared to be two individuals of the same species. But while the Green-backed Honeyeater gleans insects from leaves in the rainforest canopy, the Gibberbird wanders and feeds in the nearly bare expanses of inland gravel plain known as gibber.

For their study, the researchers found at least 20 individuals of all but one of the honeyeater species in Australia. For each of these birds they recorded details of its foraging behavior and surrounding habitat. They then used museum specimens to measure beak, wing, tail, leg, and foot characteristics of at least 6 individuals of each honeyeater species. Comparing the two datasets, they found that desert honeyeaters appear to do more with less.

The researchers’ quantitative natural history data, now publicly available on Dryad, allowed them to address their questions. “Across the board, the correspondence between a species’ morphology and its ecology is generally good,” Miller said. “But it appears that in the desert, ecological opportunity has allowed Australian honeyeaters to expand their foraging niches.” Read the Article