Museum rock wren mystery finally solved

New Zealand scientists have solved the mystery of the North Island rock wren. Today, the small groundfeeding bird is found in the

South Island mountains, where it remains above the bush line throughout its life and is the only true alpine bird in New Zealand, according to NZ Birds Online.

But there is a single rock wren specimen in an English museum that was collected at ‘‘Rimutaka’’ in the lower North Island, Remutaka by current spelling. At least, that’s what the label says.

If the label is accurate, then it’s significant because the bird is not found today on the North Island – and there’s no evidence that it ever lived there.

Rock wrens (tuke, Xenicus gilviventris) are nationally endangered, meaning they face high risk of extinction in the short term.

If their range once included the lower North Island, then they were probably wiped out by introduced pests such as the kiore (pacific rat) and weasels, according to a research paper written by Alexander Verry of the palaeogenetics lab at the University of Otago and many senior collaborators.

As scientists seek to conserve the species, they might transfer rock wrens to their former ranges, including to the lower North Island if appropriate.

Rock wrens have been ‘‘translocated’’ to Secretary Island in Fiordland, for example.

It’s not known who collected the United Kingdom bird – or when – but it was part of the collection of Walter Rothschild, a well known and immensely rich zoological collector.

Rothschild donated the North Island rock wren to the institution that became the Natural History Museum at

Tring in Hertfordshire in about 1937.

The chances are good that the specimen was sold to Rothschild by Henry Hamersley Travers, who sold him numerous New Zealand species, including some South Island rock wrens that now reside in the American Museum of Natural History in New York City.

Unfortunately Travers has a reputation for poor record keeping, Verry writes. Travers, for example, incorrectly label penguins and a snipe sold to Rothschild.

Moreover, and this is speculation, the seller had a financial incentive to mis-label the bird.

If Rothschild already had South Island tuke in his collection, the seller could get another round of cash by claiming the same species was a different species.

In any event, Verry and team solved the mystery using Otago’s ancient DNA lab and rock wren specimens from Tring, New York, Liverpool, Vienna, Te

Papa and Canterbury Museum.

The specimens are actually ‘‘bird skins’’ – where the bones and soft tissues of birds have been discarded and the skin and feathers preserved.

Preservation was incomplete but there was enough DNA for Verry’s team to amplify it for comparisons.

Turns out the North Island rock wren was actually related to a population from Fiordland.

There are 21⁄2 distinct rock wren populations – a northern South Island group, a southern South Island group, which includes a sub-family from Fiordland.

The research also proved that three tuke collected by Travers and labelled as from Otago were actually part of the northern lineages.

Other bird skins with no location data were also assigned to their lineages.

The research doesn’t prove conclusively that tuke never lived on the North Island, Verry writes.

But there’s now no evidence available to western scientists that suggests they did.

And of course, rock wrens can fly. So maybe the little one flew from Fiordland to the Remutaka Ranges, where it died.