Tiny fossil bone helps unlock history of the bowerbird

The discovery of a tiny foot bone millions of years old reveals Aotearoa New Zealand was once home to a songbird species with potentially unique courtship behaviours, new research shows.

These days bowerbirds are only found in Australia and New Guinea but an international collaboration by the University of Otago – Ōtākou Whakaihu Waka, the Museum of New Zealand Te Papa Tongarewa and the University of Cambridge shows they may have resided in Aotearoa 14-19 million years ago.

The foot bone that was found in the St Bathans, Central Otago, fossil deposits bore a close similarity to bowerbirds, though belonged to a bird that was much smaller than living species.

Co-author Associate Professor Nic Rawlence, Director of the Otago Palaeogenetics Laboratory, says this discovery provides a “wonderful and unique” insight into the biological history of Aotearoa birds.

“To many people in the world, bowerbirds were made famous by Sir David Attenborough’s nature documentaries and their elaborate courtship behaviours, where males construct an arched structure called a bower, decorated with sticks and sometimes brightly coloured objects like fruit, leaves or even pieces of plastic, all in an effort to attract a mate,” he says.

The new species has been given the name the St Bathans bowerbird (Aevipertidus gracilis), which means the gracile (slender) taxon from a lost place and age – found far from its likely close relatives in Australia and New Guinea, and long-since extinct.

“It is smaller than living and extinct bowerbirds, weighing in at 33g, compared to 96-265g for other species,” Associate Professor Rawlence says.

Its foot bone is most similar to “avenue bower builders” that include the brightly-coloured flame bowerbird and the satin bowerbird.

Lead author Dr Elizabeth Steell, of the Field Palaeobiology Lab at the University of Cambridge, says "if this bird is indeed a relative of the bowerbirds, it could represent an entirely new songbird family for Aotearoa”.

“That’s especially significant given the limited understanding we have of the ancient songbird fossil record in this region,” she says.

“The St Bathans bowerbird is the latest songbird lineage to have a long evolutionary history in Aotearoa, where the oldest members of many different groups occur here including huia, kōkako, tīeke, piopio and mohua.

“It’s likely that all these species represent the descendants of a rapid burst of evolution and dispersal from Australia to New Zealand.”

Like some of the unique animals from St Bathans, there are no living descendants left in Aotearoa.

Associate Professor Rawlence says the bowerbird would have been particularly susceptible to cooling temperatures in the lead-up to the Ice Ages and the associated changes in forest make up and distribution, which likely contributed to its extinction.

The team will continue their research on songbird fossils from St Bathans.

“This was just one fossil: there will be other songbird fossils from the site, and there might be more surprises waiting,” he says.