Extinct duck reveals how island life reshapes birds

On the remote Rēkohu Chatham Islands, an ancestral duck that arrived hundreds of thousands of years ago evolved into a sturdier, more terrestrial bird with shortened wings and elongated legs.

Within a few hundred millennia, it was already on the road toward giving up flight. The now-extinct species adds a vivid chapter to the story of how islands reshape animals.

The new research, led by the University of Otago – Ōtākou Whakaihu Waka, combines ancient DNA with detailed bone measurements to describe a previously unknown shelduck.

The species carries the scientific name Tadorna rekohu and the common name Rēkohu shelduck, both given by the Hokotehi Moriori Trust, guardians of the islands’ plants and animals.

Island life favors walkers

“In that time, the Rēkohu shelduck evolved shorter, more robust wings and longer leg bones, indicating it was going down the pathway towards flightlessness,” said co-lead author Nic Rawlence, an associate professor and director of the Otago Palaeogenetics Laboratory.

Those changes make ecological sense on Rēkohu. Food was plentiful. Ground predators were scarce. Winds were strong, and flying wasn’t the safest or most efficient choice.

“Flight is energetically expensive, so if you don’t have to fly, why bother?” said co-lead author Pascale Lubbe, a postdoctoral fellow at the University of Otago.

“The longer leg bones are more robust to support more muscle and create increased force for takeoff  – necessary when you have smaller wings.”

Bird DNA and bones tell the story

Researchers pieced together the bird’s story from two lines of evidence. First, they sequenced ancient mitochondrial DNA from Chatham Islands fossils and compared it with living relatives.

Second, they analyzed the shapes and proportions of skull, wing, and leg bones, looking for consistent differences.

Together, the genetic tree and the measurements confirm that the Rēkohu shelduck was most closely related to the pūtangitangi paradise shelduck (Tadorna variegata) of mainland Aotearoa New Zealand, yet distinct in form.

The family tree also helps time the split. The best estimate is that the ancestor of the Rēkohu shelduck colonized the islands about 390,000 years ago during the Late Pleistocene.

That is enough time, on an isolated archipelago, for natural selection and island living to reshape a bird’s body – shorter wing bones with chunkier ends and longer, more robust legs – without making it fully flightless.

Life on a windy archipelago

The Chathams sit roughly 785 kilometers (488 miles) east of mainland New Zealand and have long been a crucible of endemic bird life. Before people arrived, at least eight species of waterfowl bred there, from ducks to swans and mergansers.

Island isolation and a different predator scene often push birds toward a classic “island syndrome:” reduced flight, stronger legs, and more time on the ground.

The Rēkohu shelduck fits that rulebook. It had a longer, narrower cranium, proportionally shorter forelimbs, and longer hindlimbs than its mainland cousin – signatures of a bird that spent more time walking and foraging on foot.

Genetically, Tadorna rekohu is the sister taxon to T. variegata. Morphologically, it diverged in ways that matter for survival on Rēkohu. Ratios of limb bones show a slight tilt toward leg power over wing power.

Analyses that compare flight capability across ducks suggest the Rēkohu shelduck was flight-reduced rather than fully flightless – a sensible compromise when winds are fierce and terrestrial food is reliable.

Overhunting sealed the bird’s fate

Archaeological clues indicate the Rēkohu shelduck did not survive into the 19th century. Its bones appear in early Moriori middens, pointing to overhunting as the likeliest cause of extinction, later compounded by habitat change and introduced predators.

That fate mirrors many island birds that evolved with few enemies on the ground. Yet discovery still carries meaning.

“This discovery is great for Rēkohu as a whole and helps connect imi Moriori with miheke (treasure) of the past,” said Levi Lanauze, Hokotehi Moriori Trust CEO.

A window into rapid evolution

Describing Tadorna rekohu does more than add a name to a list. It shows how quickly island environments can nudge anatomy and behavior.

It clarifies that the Chathams hosted a richer waterfowl community than survives today. And it underscores the value of pairing ancient DNA with careful measurements to resolve long-standing taxonomic puzzles.

Each new species described from Rēkohu helps sharpen the timeline of colonization, adaptation, and loss on an archipelago where evolution works fast.

The Rēkohu shelduck also illustrates how science and community can work together. The bird’s names acknowledge guardianship and genealogy that bind people, place, and wildlife.

As researchers continue to study bones, genomes, and sediments from the islands, more stories like this are likely to surface – reminding us how landscapes shape species, and how quickly those species can vanish without careful stewardship.

The study is published in the Zoological Journal of the Linnean Society.

Image credit: Sasha Votyakova, Te Papa CC BY 4.0

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–