Chatham petrels: Success at Sweetwater

The recent hatching of a Chatham petrel chick in the Sweetwater Conservation Covenant on Chatham Island is another significant step in the long road to recovery for one of the world’s rarest seabirds.

In decline

Probably once abundant throughout the Chatham Islands, human exploitation, habitat destruction and introduced predators saw the species restricted to Rangatira Island by the time of its discovery in 1892. 

A Chatham petrel chick tucked up in its down duvet

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.

Detering 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.

The competition: a broad-billed prion outside its burrow

Natural burrows converted into ‘state houses’

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 was futile.

Wetsuits work

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%.

A Chatham petrel squeezing through the anti-prion flap into its burrow

New colonies

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.

Rangatira Island (left) and Caravan Bush (right) on Pitt Island

Return of Chatham petrel to “Sweetwater”

Once the success of the Pitt Island translocation was evident work started on the return of Chatham petrel to “Sweetwater” on Chatham Island in 2008.

Ranger Antje Leseberg checking the band on an adult Chatham petrel

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. As at Caravan Bush, petrel sounds played over loudspeakers encouraged returning petrels to land at the site.

The first indication of success at Sweetwater was seen last autumn when a pair of petrels were seen in a burrow. After wintering off the South American coast, the pair have returned to Sweetwater and laid an egg in February.

Taiko Trust members were delighted to find a chick present during burrow checks in early March. All going well this chick should fledge in May and spend 2-3 years at sea before returning to Sweetwater. By then it should have more company, as four more burrows show signs of activity, surely signalling the sweet smell of success.