The mystery of Manawatāwhi mollymawks: a history and field report

These majestic giants spend up to 85 percent of their lives far beyond land out on the open ocean, gliding effortlessly in search of food. Yet tragically, most albatross species (19 out of 24) are threatened with extinction, largely as a result of being killed in interactions with fishing boats or eaten at their breeding sites by introduced mammalian predators. Albatrosses breed on remote oceanic islands, as far from humans as possible. Despite this isolation, most breeding sites are known, and many are monitored to track the birds’ numbers, making it unusual in New Zealand, or globally, that a new albatross population should be discovered and remain unstudied.

In December 1983, such an event happened when Anthony Wright, then Curator of Botany at Auckland War Memorial Museum, ventured ashore on a rock stack that forms part of a chain of islands north of New Zealand known as Manawatāwhi (Three Kings Islands). The rock, named Rosemary after the yacht that had transported Auckland Museum field parties to Manawatāwhi in the 1940s and 50s, is clothed in unique salt tolerant vegetation that Wright was keen to document at the time. It was with some dismay that Wright, possessing a self-confessed bird phobia, was distracted from his botanising by a “strident, duck-like calling” near the summit. Upon investigation he discovered six very large seabirds occupying nests, and took photographs and made detailed observations and sketches. Two years later, others were able to land on Rosemary Rock and collect bill measurements. New Zealand’s bird experts drew into a huddle and concluded that the birds were most likely Buller’s albatross.

Image credit: Featured in the Journal of the New Zealand Ornithological Society Notornis (31) (Wright 1984)

The Buller’s albatross (Thalassarche bullerii) is named after famed bird collector, researcher, and enthusiast, Sir Walter Buller. Quirkily, in New Zealand the species is more commonly known as Buller’s mollymawk. The term mollymawk comes from a 17^th century Dutch term mallemok, which translates as foolish (mal) gull (mok). Mollymawks are a group of medium-sized albatrosses of which Aotearoa has an abundance, only two of the world’s nine mollymawk species do not breed here. The Buller’s mollymawk is one of New Zealand’s more numerous species, particularly in its southern waters as their breeding colonies are found on the Chatham and New Zealand sub-Antarctic islands.

Finding a small colony of this predominantly “southern” mollymawk at the top of the North Island and over 1000 kilometres from any other breeding site, was puzzling to say the least. Particularly, which of the major albatross populations were these birds were related to? In the 1980s, it was recognised that not all Buller’s mollymawks were alike.  Birds from the Chatham Islands can be separated from their southern counterparts by differences in bill size, plumage colouration and breeding timetable. Recent genetic analyses have also supported this split, showing Chatham and sub-Antarctic populations are genetically distinct. As a result, they have both been recognised as distinct subspecies: Northern Buller’s mollymawk (Thalassarche bulleri platei) and Southern Buller’s mollymawk (Thalasarrche bulleri bulleri).  Scientists use the term subspecies when they consider populations are different enough to have branched off biologically (i.e., colour, timing of breeding, different DNA), but are similar enough that they could still interbreed with each other if they had the opportunity. However, although albatrosses travel vast distances, they are very much homebodies when it comes to their breeding sites, so interbreeding is unlikely.  

Image credit: Buller’s mollymawk in flight. Edin Whitehead

All of this adds uncertainty to exactly what the Buller’s mollymawks of Rosemary Rock are.  Are they Northern or Southern subspecies, or something different? Such questions are where the rubber hits the road in terms of the relationship between taxonomy (the science of describing and naming biodiversity) and conservation biology (the science of protecting that diversity). Conservation funding and effort is typically based on population size and change of known and described species. If the albatrosses of Rosemary Rock were found to be related to large populations further south, then they would be of lower conservation priority.  However, a tiny population of genetically distinct albatrosses, restricted to one rock stack, would immediately be considered of high conservation concern, possibly even critically endangered.  

Fast forward 37 years to 2020 and we still don’t have that vital information for the Rosemary Rock birds. While this might seem surprising, it is not an unusual situation in our small nation, where important wildlife questions are often left unanswered due to a small pool of researchers, an even smaller pool of funding, and, in this case, the remoteness of the birds in question. However, over the course of several years, Auckland Museum and mana whenua of Manawatāwhi, Ngāti Kuri, had been working on a plan to fill in the blanks. This, of course, would require getting back onto Rosemary Rock, not a simple undertaking. Manawatāwhi lies on an undersea submarine plateau known as the King Bank, 60 kilometres north of Te Rerenga Wairua (Cape Rēinga) at the intersection of the Tasman Sea and South Pacific Ocean. The group is made up of 13 islands and a number of rock stacks, none of which have beaches or easy landing sites. Rosemary Rock is in the Western chain of islands known as the Princes Group. Windswept and completely exposed to Southern Ocean swells, this 50-metre-high lump of basalt, bounded by cliffs, presents a serious challenge to land on, even for experience field researchers.

Image credit: Rosemary Rock, Manawatāwhi​. Jenn Carol

And then, after a frantic day’s work, we made our exit, climbing back down the rock, executing a well-timed dive and swimming back to the boat for the long journey back to Houhora, exhausted but extremely satisfied.

The next phase of this work on Buller’s mollymawk will move to the lab, where DNA from the collected blood samples will be sequenced and compared with DNA from both subspecies on the Chatham and sub-Antarctic Islands. These results will, finally, provide an answer to the near 40-year-old question of the whakapapa of the Mollymawks of Rosemary Rock. 

Image credit: Projectile vomiting chicks on their nests. Kevin Parker, Parker Conservation