Bones strewn through fossil deposits in Northland and museum collections belong to a previously undescribed and extinct species of shag, researchers have concluded.
By examining bone shape and using DNA, they found that there was an entirely different species, dubbed the kōhatu shag (Leucocarbo septentrionalis).
It was previously thought that the remains were those of the king shag (Leucocarbo carunculatus), which lives at the top of the South Island.
The study involving Otago University, Canterbury Museum, Te Papa and Auckland War Memorial Museum has been published in the international journal Molecular Phylogenetics and Evolution.
Researchers say analyses show the king shag was formerly widespread around the southern North Island and northern South Island.
However, it experienced population and lineage extinctions, and range contraction, probably after Polynesian arrival.
"This history parallels range contractions of other New Zealand seabirds," the study said.
"Conservation management of the king shag should take into account this species' narrow distribution and probable reduced genetic diversity."
Analyses of prehistoric material from mainland New Zealand suggested that the now extinct northern New Zealand Leucocarbo populations comprised a unique lineage.
"Although these distinctive populations were previously assigned to the king shag, we herein describe them as a new species, the ke kōhatu shag," the researchers said.
"The extinction of this species further highlights the dramatic impacts Polynesians and introduced predators had on New Zealand's coastal and marine biodiversity."