Research that began sixteen years ago has, at long last, determined what Matt Rayner (Curator, Land Vertebrates) suspected all along – they may look alike, they may sound alike, but Pterodroma cookii cookii and P. c. orientalis are not the same bird. 


Within the international ornithological community, New Zealand is famous for its birds, and particularly seabirds. Our little island nation has the highest number of endemic breeding seabirds in the world – over 14 million breeding pairs. As with our land birds, our seabirds have also become greatly threatened since first human contact and we now have more threatened seabird species than anywhere else in the world. Against this backdrop, every single species must compete for conservation dollars, and often unwittingly rely on specialist researchers to champion their cause. 

For the Cook’s petrel, that specialist is the Museum’s own Matt Rayner. After starting his doctoral research in 2004 on the two Cook’s petrel populations, Rayner began documenting distinct differences in behaviour and biology between them. According to Māori oral history, observations of the first European settlers and Holocene deposits in cave and dune systems, the Cook’s Petrel used to breed and thrive in vast colonies right along the length of New Zealand. Today they are only found in the very north (on Te Hauturu-o-Toi/Little Barrier Island) and the very south (Whenua Hou/Codfish Island) of their formerly expansive kingdom. 

Rayner observed that birds breeding on Hauturu were smaller than their southern counterparts, bred over one month earlier and both populations had distinct differences in their mitochondrial DNA, the small circular chromosomes found inside mitochondria, the energy packs of animal cells. With the help of new micro-tracking technology, Rayner began tracking these small, 200-gram seabirds far out beyond land and discovered that during breeding, adult birds remained separated in their movements at sea at the northern and southern ends of New Zealand. At the end of the breeding season, however, something even more spectacular happened: birds from Hauturu made a 64,000-kilometre journey to the north Pacific Ocean, whereas birds from Whenua flew east, thousands of kilometres to oceanic waters off the coast of South America. The birds were responding to seasonal changes in oceanic productivity over a vast scale that made it rewarding to travel vast distances to places where there is an abundance of food. 


Image: Pterodroma cookii; LB4290; © Auckland Museum CC BY


In 2011, Rayner wrote a paper hypothesising that time and altered feeding and migration schedules and destinations had resulted in two defined, genetically distinct populations of Cook’s petrel. Young Cook’s petrels are unlikely to follow other birds on their first migration, but where birds fly is anything but a whim — they are guided by an inherited internalised ancestral memory, which, scientists are now seeing, keep them oriented to the same direction year after year. 

The science of describing species boundaries - taxonomy - has clear rules, and one stone that remained unturned for the Cook’s petrel was an analysis of nuclear DNA, found in the nucleus of animal’s cells. Nuclear DNA mutates at a rate approximately 100 times more slowly than mitochondrial DNA and is thus the definitive test for revealing if populations of animals have been genetically isolated for evolutionarily significant time spans.

Rayner and his team analysed the genetic relationship between the two Cook’s petrel populations using nuclear DNA and found what scientists call significant population structure – differences at an ancient level. They also extracted mitochondrial DNA from old bones of Cook’s petrel uncovered at historical deposits all over New Zealand and were able to show that prehistorically, birds from Hauturu were only found in the North Island. This result, together with all the previous information on Cook’s petrel, gave the researchers confidence in declaring the two Cook’s petrel populations as distinct subspecies with the scientific names Pterdroma cookii cookii for birds from Hauturu, and Pterodroma cookii orientalis for birds from Whenua Hou.

This is not merely a philosophical exercise. Whilst some consider the science of taxonomy dry, the work Museum and university researchers conduct to describe biodiversity has literal life-and-death consequences. The world is currently undergoing a biodiversity crisis with human activities pushing vast numbers of species to extinction.  An essential tool in the fight against this biodiversity loss is a taxonomic understanding of what biodiversity exists, what species live where and how populations differ from each other.  Only with this information can scarce conservation dollars be assigned. And while there is more than a little irony in the fact that species must now rely on humans to save them when it is largely humans who are to blame for their dwindling numbers, discoveries like these may make all the difference.

Header image: Pterodroma cookii; LB6477; © Auckland Museum CC BY​
Background image: © Abe Borker