‘Use it or lose it’: How an island changed a bird species

The discovery of yet another unique animal species from Rēkohu Chatham Islands illustrates how the physical qualities of an animal are influenced by its surroundings.

New research led by the University of Otago – Ōtākou Whakaihu Waka describes a new, extinct shelduck whose ancestors arrived on the islands 390,000 years ago.

While this may seem like a short period of time, co-lead author Associate Professor Nic Rawlence, Director of the Otago Palaeogenetics Laboratory, says it is long enough to impact the species.

“In that time the Rēkohu shelduck evolved shorter, more robust wings and longer leg bones indicating it was going down the pathway towards flightlessness,” he says.

These changes were due to a range of factors, such as an abundance of food, lack of ground-dwelling predators, and windy conditions, so flying was not the preferred option.

Co-lead author Dr Pascale Lubbe, also of the Otago Palaeogenetics Laboratory, says in a case of “use it or lose it, the wings start to reduce”.

“Flight is energetically expensive, so if you don’t have to fly, why bother,” she says.

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

Researchers used ancient DNA and analysed the shape of the bones to determine the Rēkohu shelduck is most closely related to the pūtangitangi paradise shelduck from Aotearoa New Zealand.

The Rēkohu shelduck spent more time on the ground than its cousin and became extinct prior to the 19^th century due to over-hunting and predation.

The study is published in the Zoological Journal of the Linnean Society and adds to the islands’ rich history as a home to many species of waterfowl before human settlement.

The shelduck’s scientific name (Tadorna rekohu) and common name (Rēkohu shelduck) were gifted to researchers by the Hokotehi Moriori Trust who are tchieki (guardians) of the plants and animals on Rēkohu Chatham Islands, with which they are interconnected through shared hokopapa (genealogy).

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

The study is an international collaboration between Otago, the Museum of New Zealand Te Papa Tongarewa, The University of Adelaide, and Manaaki Whenua Landcare Research.