The Paradise shelduck, Tadorna variegata, the closest relative of the Rēkohu shelduck
Remote islands are the sort of environment biologists might dream up if asked to design a natural laboratory for testing evolution. It’s no coincidence that Darwin was inspired to develop his theory while visiting the Galápagos Islands and noticing how the finches had adapted in different ways to the conditions on each island.
Another striking example comes from the Rēkohu Chatham Islands, about 785 kilometres east of mainland Aotearoa New Zealand. The islands rose in their present form around 3.5 million years ago, effectively resetting the clock for the ecosystems that would develop there. Species arriving from elsewhere had to make do with what traits they already carried, and only those suited to island life survived. Most new arrivals were birds, insects, or wind-blown plants carried there by chance. With few predators and limited competition, these colonists had the perfect opportunity to go their own evolutionary way.
The Chatham Islands (Rēkohu / Wharekauri).Because such populations start from just a handful of individuals, they represent only a small slice of the genetic variation in the parent species. This lack of genetic diversity is a double-edged sword: it means that whatever traits the founders happen to carry get amplified quickly (the founder effect), but it also leaves the population vulnerable. Add in genetic drift—the chance changes in allele frequency that are strongest in small populations—and you have a recipe for rapid divergence from the original stock. In other words, the textbook definition of evolution playing out in real time.
- Location: ~785 km east of mainland Aotearoa New Zealand in the South Pacific.
- Main Islands: Chatham Island (Rēkohu, Wharekauri) and Pitt Island (Rangiauria), plus several smaller islets.
- Area: About 966 km² (roughly the size of Hong Kong).
- Geological history: Current form dates to ~3.5 million years ago; volcanic and uplifted seafloor origins.
- Climate: Cool, wet, and windy maritime climate, strongly influenced by the Southern Ocean.
- Biodiversity:
- Many unique (endemic) species of birds, plants, and invertebrates.
- Historically no land mammals apart from seals and bats, meaning birds often filled ecological niches elsewhere occupied by mammals.
- Human history:
- First settled by Polynesians around the 15th century, who became the Moriori, developing a distinct culture of non-violence and sustainable living.
- European contact in the 18th century brought massive change, disease, and ecological disruption.
- Modern population: About 600 people today, mostly on Chatham Island.
For anyone who still clings to creationist ideas, these natural “experiments” pose an awkward problem. How else can we explain the sudden appearance of unique island species, their clear descent from mainland relatives, their rapid divergence under isolation, and their eventual extinction—all on a timescale of a few hundred thousand years—without evolution? The Chatham Islands, like the Galápagos before them, are a reminder that the evidence for evolution is written into the very fabric of the natural world.
The flip side of these natural laboratories is, of course, their fragility. Species that evolve in these isolated, predator-free environments can be highly specialised, poorly equipped to cope with change, and easily driven to extinction. When humans first landed on the Chathams, there were 64 breeding bird species, 34 of which lived nowhere else. Today, many of those unique birds are gone. Most recently, a team of New Zealand scientists has added the extinct Rēkohu shelduck to the list, showing how a species can appear, adapt, and vanish again in the space of about 390,000 years.
Their findings are published, open access, in the Zoological Journal of the Linnean Society. Four of the authors have also written about their work in The Conversation, where they explain what this discovery tells us about the richness—and the vulnerability—of island life.
The discovery of an extinct shelduck highlights the rich ancient biodiversity of the remote Rēkohu Chatham Islands
An artist’s depiction of the Rēkohu shelduck.
Credit: Sasha Votyakova/Te Papa, CC BY-ND
Islands are natural laboratories where evolution can run rampant as plants and animals adapt to new environmental conditions and vacancies in the ecosystem.
This creates all manner of unique animals, although sadly extinction rates are high on islands and many species are now gone. Examples include a blind, flightless duck with a sensory bill (like a platypus) on Hawaii, and pygmy mammoths on islands off the coast of southern California.
The Rēkohu Chatham Islands, an archipelago 785 kilometres east of mainland Aotearoa New Zealand, are no exception.
The islands were once home to a rich assemblage of unique birds, with 64 breeding species at the time of human arrival. Some 34 species and subspecies were found nowhere else on Earth.
This includes the endangered parea Chatham Island pigeon and the extinct mehonui Hawkin’s rail.
Our new research adds a unique species of shelduck to this group and illustrates just how quickly birds can adapt to life on isolated islands.
The Rēkohu Chatham Islands rose above the waves, taking their present form, around 3.5 million years ago. The archipelago is an ideal place to observe how ecosystems form and new species evolve.
The windswept Rēkohu Chatham Islands are home to many bird species that are found nowhere else.
Alan Tennyson/Te Papa, CC BY-NC-ND
Other birds underwent major changes, such as the extinct Chatham Island duck, which was large, flightless and had bony spurs on its wings which were probably used in fights over territory.
Evolution of the Rēkohu shelduck
Shelducks are a group of semi ground-dwelling ducks found in Eurasia, Africa, Australia and the New Zealand region. In Aotearoa, they are represented by the familiar pūtangitangi paradise shelduck.During the 1990s, Museum of New Zealand Te Papa Tongarewa palaeontologist Phil Millener found isolated bones and associated skeletons of an extinct shelduck in the rich fossil deposits around the Chatham Islands archipelago. He noted the bones may belong to a new species and they were archived at the museum until scientific advances allowed us to test this idea.
Bones of the extinct Rēkohu shelduck compared to the pūtangitangi paradise shelduck. In each pair the left and right bones are the Rēkohu and paradise shelducks, respectively.
Jean-Claude Stahl/Te Papa, CC BY-NC-ND
On evolutionary scales, 390,000 years is not a long time, but it was long enough for the Rēkohu shelduck to go down its own evolutionary path. Like the paradise shelduck, males were bigger than females, but the Rēkohu shelduck was taller and more robust. These changes meant Rēkohu shelducks were poorer fliers than their mainland cousins.
Flight is energetically expensive. It is often lost when the cost outweighs its advantages. This is part of the “island syndrome”, a suite of changes in bone shape and behaviour observed in island species. On Rēkohu, an abundance of food, strong winds and a paucity of large predators meant flying wasn’t as beneficial as on the mainland, where predators such as kērangi Eyle’s harrier, Haast’s eagle, whēkau laughing owl and adzebill abounded.
Over time, a preference to spend more time on the ground resulted in the wing bones of the Rēkohu shelduck becoming shorter, more robust and less able to support flight. At the same time, its leg bones became longer and more robust. The Rēkohu shelduck was on a trajectory to flightlessness when it became extinct shortly after humans arrived.
A rich Rēkohu waterfowl community
Sand dunes are a rich source of subfossil bird bones that can be used to reconstruct the past biodiversity of Rēkohu.
Alan Tennyson/Te Papa, CC BY-NC-SA
Our lab continues to investigate the fauna of the islands, with ongoing work to determine if an extinct falcon represents another unique Rēkohu bird.
Working with Indigenous communities is paramount if we are committed to the process of decolonising palaeontology. The shelduck’s scientific (Tadorna rekohu) and common (Rēkohu shelduck) names were gifted to us by the Hokotehi Moriori Trust, the tchieki (guardians) of Rēkohu biodiversity, with which they are interconnected through shared hokopapa (genealogy).
The discovery and naming of the Rēkohu shelduck helps connect the Moriori imi (tribe) with miheke (treasure) of the past, allowing people to reclaim some of the pages of their biological heritage that have been lost.
The Rēkohu shelduck is part of a rich native and endemic waterfowl assemblage (nine different species) that was present when people arrived. These birds are survived only by the parera grey duck. We are only just beginning to understand how the ecological community of the islands once functioned.
The Rēkohu shelduck was on a unique evolutionary trajectory when it went extinct after humans colonised the islands but prior to the arrival of Europeans and Māori. This is a fate shared by many of Rēkohu’s birds.
The discovery of the Rēkohu shelduck is a demonstration of the speed at which island species can be changed by their environment. It highlights both the distinctiveness of Rēkohu animals and their close relationship with mainland Aotearoa New Zealand.
Nic Rawlence, Associate Professor in Ancient DNA, University of Otago; Alan Tennyson, Curator of Vertebrates, Museum of New Zealand Te Papa Tongarewa; Levi Lanauze, Chief executive of Hokotehi Moriori Trust, Indigenous Knowledge, and Pascale Lubbe, Postdoctoral Research Fellow in Molecular Ecology, University of OtagoThis article is republished from The Conversation under a Creative Commons license. Read the original article.
What makes studies like this so devastating for creationism is that they don’t just provide abstract evidence for evolution — they show the process unfolding in miniature, on islands that act like natural laboratories. The Rēkohu shelduck wasn’t specially created; it was an offshoot of a known mainland species that adapted to new conditions, flourished for a time, and then disappeared. Its story is written in the rocks, the genes, and the fossils. No divine intervention is required; the facts are exactly what evolutionary biology predicts, and exactly what creationism cannot explain.AbstractIntroduction
The Rēkohu Chatham Islands, 785 km east of mainland Aotearoa New Zealand, exhibit high levels of species endemism. Prior to human settlement, the islands supported a rich waterfowl fauna comprising at least eight anatid species. Here we describe a new extinct duck from Holocene fossil bone deposits on the Chatham Islands. Geometric morphometric analyses and phylogenetic analysis of complete mitogenomes confirm that the Rēkohu shelduck (Tadorna rekohu sp. nov.) was the sister-taxon to the pūtangitangi paradise shelduck Tadorna variegata (Gmelin, 1789) from mainland New Zealand. The ancestors of the Rēkohu shelduck colonized the Chatham Islands around 390 000 years ago during the Late Pleistocene. Comparatively short, robust wing bones and long leg bones indicate that the species was flight-reduced relative to their mainland congener. The presence of Rēkohu shelduck bones in early Moriori midden deposits suggests its extinction was due to over-hunting prior to the later European and Māori settlement of the islands in the 19th century.
The Rēkohu Chatham Islands are an isolated archipelago 785 km east of mainland Aotearoa New Zealand, and comprise the main Chatham Island, as well as Rangihaute Pitt, Maung’ Re Mangere, Tapuaenuku Little Mangere, Hokorereoro South East Islands, and various islets. The islands were completely submerged during the Late Miocene to Early Pliocene. Subsequent tectonic activity caused the island archipelago to re-emerge less than 3 Mya (Campbell 2008, Campbell et al. 2008.1, 2009, Landis et al. 2008.2). Mean dispersal-time estimates for avian lineages on the islands range from 40 Kya to 2.55 Mya (Baker et al. 2010, Alstrom et al. 2018), with one outlying study of three flightless rails that reports dates as far back as 9.5 Mya (Garcia et al. 2014). This discrepancy with the date of island emergence is probably due to unsampled sister-taxa and/or extinction of sister-taxa [reviewed by McCulloch and Waters (2019); see also Slater et al. (2009.1) cf. Austin et al. (2013) for Malvinas’/ Falkland Islands’ example].
Radiocarbon ages of human-associated materials from the Chatham Islands demonstrate that the islands were settled by Moriori prior to ~ce 1500 (Wilmshurst et al. 2011, Rawlence et al. 2016). At that time, eight currently recognized native or endemic waterfowl species bred on the islands (Miskelly et al. 2024). The majority of these taxa also occurred on mainland New Zealand: the native pārera grey duck (Anas superciliosa), pāpango New Zealand scaup (Aythya novaeseelandiae), New Zealand pink-eared duck (Malacorhynchus scarletti), kuruwhengi Australasian shoveler (Spatula rhynchotis), and pāteke brown teal (Anas chlorotis). However, several endemic waterfowl were also present: the Chatham Island duck (Anas chathamica), poūwa (Cygnus sumnerensis chathamicus), and Chatham Island merganser (Mergus milleneri) (Miskelly et al. 2024). Bones of an undescribed shelduck (Tadorna spp.) have been found in Holocene fossil and archaeological midden deposits on the Chatham Islands (Tennyson and Millener 1994, Millener 1999, archaeological specimen NMNZ S.31481). The settlement of the islands by Moriori, and later by Europeans and Māori, resulted in widespread faunal extinctions as a consequence of over-hunting, habitat destruction, and predation from introduced terrestrial mammals (Tennyson and Martinson 2007, Rawlence et al. 2016). All the original waterfowl species on the Chatham Islands, save the grey duck, are now extinct on the archipelago.
On mainland New Zealand, bones attributed to the pūtangitangi paradise shelduck Tadorna variegata (Gmelin, 1789) have been found in Holocene fossil and archaeological midden deposits across the North and South Islands, indicating a widespread natural distribution (Williams 1971, Worthy 1999.1). However, the form that inhabited the Chatham Islands prior to its extinction has long been suspected to be a different species to that occurring on mainland New Zealand (‘undescribed Tadorna species’; Tennyson and Millener 1994, Millener 1999). Millener (1999) suggested that the shelduck from the Chatham Islands was a weaker flyer (i.e. ‘island syndrome’ effects) than T. variegata but provided no quantitative analyses beyond figuring a cranium (NMNZ S.32830, ‘presumably male’) from Maunganui, Chatham Island next to one of T. variegata (NMNZ OR.16473, male). The identity of shelduck bones from the Chatham Islands remains taxonomically unresolved (Miskelly et al. 2024).
Shelducks in the genus Tadorna are semi-terrestrial ducks with a worldwide distribution (Fig. 1). Tadorna comprises the common shelduck Tadorna tadorna (Linnaeus, 1758) and ruddy shelduck T. ferruginea (Pallas, 1764) from Europe, Asia, and North Africa; the South African shelduck T. cana (Gmelin, 1789); the critically endangered crested shelduck T. cristata (Kuroda, 1917) from eastern Russia and east Asia; the chestnut-breasted shelduck T. tadornoides (Jardine and Selby, 1828) from Australia; and the aforementioned T. variegata from New Zealand. The Radjah shelduck Radjah radjah (Garnot and Lesson, 1828), previously Tadorna radjah, from Australia and New Guinea, is now recognized within a monotypic genus (Sraml et al. 1996).
In this study, we conducted multivariate, geometric morphometric analyses of cranial and postcranial Tadorna bones from the New Zealand region. We sequenced and analysed the mitochondrial cytochrome c oxidase subunit I (COI) gene, and subsequently the mitogenome of Chatham Islands Tadorna, within a phylogenetic framework of Tadorna shelducks. Using this combined dataset, we resolve the taxonomic status of shelduck bones from the Chatham Islands. We predict that the Chatham Islands form will (i) be most closely related to T. variegata based on geographical proximity, and (ii) exhibit morphometric signatures of ‘island syndrome’ effects such as reduced flight ability. Finally, we discuss the history and former composition of the waterfowl assemblage on the islands.
Figure 1. Schematic of the breeding and year-round distribution of Tadorna shelducks. The Rēkohu Chatham Islands (orange circle) are located 785 km east of Aotearoa New Zealand. Distributions are based off the Cornell Lab of Ornithology Birds of the World website. Symbol: †, extinct.
Nicolas J Rawlence, Pascale Lubbe, Amy L Adams, Lara D Shepherd, Theresa L Cole, Michael Knapp, Bastien Llamas, Jamie R Wood, Kieren J Mitchell, Alan J D Tennyson
Ancient DNA and morphometrics reveal a new species of extinct insular shelduck from Rēkohu Chatham Islands Zoological Journal of the Linnean Society 204(3), (2025), zlaf069, https://doi.org/10.1093/zoolinnean/zlaf069
Copyright: © 2025 The Linnean Society of London / Oxford University Press.
Published by Oxford University Press. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
This leaves creationists like Ken Ham of Answers in Genesis, Kent Hovind of Creation Science Evangelism, and the Intelligent Design advocates Michael Behe and William Dembski of the Discovery Institute in an impossible corner. Their insistence that species were created in fixed “kinds” collapses under the weight of evidence showing species diverging, adapting, and going extinct within just a few hundred thousand years. The Rēkohu shelduck isn’t some obscure exception; it’s one example among many, repeated across islands worldwide from the Galápagos to Hawaii to the Chathams. Each case lands another blow, and the cumulative evidence is overwhelming.
At this stage, creationism resembles a brain-dead boxer who has already been counted out. The referee has declared the fight over, the crowd has gone home, and yet the poor fighter is still flailing around in the ring, convinced he’s still in with a chance. Ham may still rant about “God’s Word,” Hovind may still peddle pseudoscience in his seminars, Behe may still wave around “irreducible complexity,” and Dembski may still invoke “specified information,” but the reality is that science long ago delivered the knockout. Every new discovery like the Rēkohu shelduck isn’t just another punch; it’s another reminder that the match is finished and evolution won by a clean, decisive knockout.
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