New Zealand's little blue penguins are actually Australian invaders, according to researchers from the University of Otago. In hopes of figuring out when the adorable penguins first arrived, researchers analyzed DNA from the remains of more than 100 little penguins, popularly known as "little blue penguins," including bones dating to pre-human times and specimens from archaeological deposits and museums, according to the university's news release.

"Our results clearly show that the Australian penguin colonized Otago very recently, between 1500 and 1900 AD, apparently following the decline of the native New Zealand little penguin, which was hunted by early human settlers and introduced predators," Dr. Stefanie Grosser, who conducted the study as a Ph.D. researcher in Otago's Department of Zoology, explained in the release, adding, "Amazingly, all of the bones older than 400 years belong to the native New Zealand species."

Little penguins (Eudyptula minor) are the world's smallest penguins, measuring only 13 inches tall on average and weighing just a bit over one kilogram.

The Australian little blue penguins – Eudyptula novaehollandiae – were hard to visually distinguish from the native New Zealand ones - Eudyptula minor. In fact, until recently, they were thought to be a single species. However, their unique behaviors and calls set them apart.  

"That distinct behavior where the penguins come ashore in big rafts of 100 or 200 - that's the Australian one," Professor Jonathan Waters of the University of Otago, who led the study, added in a statement. "The Australian ones can breed twice a year, while the native New Zealand one can only breed once."

Researchers estimate the Aussie invaders started off with a population of about 3,000 penguins; however, they are still unsure how the little penguins managed to conquer New Zealand. Waters explained it may in part be due to the fact that little penguins have a tendency to travel great distances and to congregate in large groups.

While there is still more work to be done, Waters concluded, "The really exciting thing about these findings is that they show how quickly nature can respond to human impacts."

Their study was recently published in the journal Proceedings of the Royal Society B: Biological Sciences.

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