Probably once abundant throughout the Chatham Islands, human exploitation, habitat destruction and introduced predators saw the Chatham petrel restricted to Rangatira or Southeast Island by the time of its discovery in 1892.
Until 1961 farming activity on Rangatira resulted in the petrels being confined to small forest patches, where they competed for burrows with the similarly sized broad-billed prion. Nesting at different times of the year, many petrel chicks were ousted from their burrows by returning prions. By 1990 the Chatham petrel population was estimated to be around 1,000 birds and heavily outnumbered by some 600,000 broad-billed prions.
Studies found that while adult Chatham petrel survival was high, less than 50% of pairs were managing to fledge a chick, placing the population in peril. So, finding a way to deter prions from entering Chatham petrel burrows was a priority.
Natural burrows were converted into wooden 'state houses' with plastic pipe entrances, to aid inspection of the contents, and efforts were made to dissuade prions from using them by removing any found within and relocating some distance away. This required frequent nightly inspections of the petrel burrows and numerous DOC staff and volunteers will have memories of the nightly burrow rounds, clumping around the forest with ungainly petrel-boards attached to their footwear to avoid crushing the numerous seabird burrows. It proved futile, with prions soon returning to the burrows and killing the chicks.
Lincoln University researchers finally came up with a simple solution – stretching a piece of neoprene wetsuit material over the entrance of the burrow pipe and cutting a slot just large enough for a petrel to squeeze through. It has proved remarkably effective, the petrel 'homeowner' tolerates the inconvenience of a tight squeeze, but prospecting prions are deterred by it. This, along with barricades erected while the petrels are away over the winter has increased nest success to around 90%.
The relative abundance of Chatham petrel chicks has since allowed for the next phase of recovery, the creation of new colonies on Pitt and Chatham Islands.
200 chicks were translocated to new homes in the predator-proof Elizabeth Ellen Preece Conservation Covenant (aka Caravan Bush) on Pitt Island between 2002 and 2005. Hand-fed until ready to fledge, the chicks remembered Caravan Bush as their new home and some returned after two or three years at sea with the first pair breeding in 2005. In 2012, 17 pairs bred producing 15 chicks.
Once the success of the Pitt Island translocation was evident work started on the return of Chatham petrel to Chatham Island in 2008. In partnership with the Chatham Island Taiko Trust another 200 Chatham petrel chicks were moved over 4 years to nest boxes within a 4ha predator-proof enclosure built by the Trust at Sweetwater. As at Caravan Bush, petrel sounds played over loudspeakers encouraged returning petrels to land at the site. In 2011 a pair bred for the first time, successfully fledging their chick in June 2012.
With threats managed on land, some attention has also been given to investigating what threats Chatham petrels might face at sea, e.g. interaction and mortality associated with the fishing industry. Since nothing was known about the at-sea distribution of the species, researchers from Auckland University and DOC attached small tracking devices to adult petrels to track their movements over an entire year.
The results showed that when breeding, Chatham petrels foraged relatively closley to the Chathams, but over winter migrated east and north to areas 1000km from the coast of Peru and Chile. It seems that unlike many of the larger petrels and albatross, Chatham petrels are not directly affected my mortality associated with fisheries.
The new colonies and ongoing management of the Rangatira population will see ongoing population growth. Future translocations to Mangere Island and large predator-free enclosures on Chatham Island should see the long-term security of the species realised.
- Rayner, M.J. et al., 2011. The breeding cycle , year-round distribution and activity patterns of the endangered Chatham Petrel ( Pterodroma axillaris ). Emu, 112(2), pp.107-116.