New Zealand has an amazing diversity of seabirds. Around 1/3 of the worlds 348 species are found in New Zealand waters, with a high number of endemic and threatened species among them. Te Papa has a long-term research programme on Westland Petrels, a species that nests in the coastal cliffs near Punakaiki, on the West Coast of the South Island.
This year we visited the colonies in April, just after very violent storms had damaged a lot of forest in Westland, with a high level of damage to indigenous forests throughout the region. Sadly, the Westland Petrel habitat was not spared, and damage to the canopy trees in the two colonies monitored by the Te Papa science programme was very apparent. The majority of the canopy trees in the study colony were toppled, and all the scrubs and tree ferns were stripped of foliage. All the debris was thickly strewn over the forest floor. As researchers that had visited these site over many years, my colleague Kerry-Jayne Wilson (coordinator of the West Coast Blue Penguin Trust) and I were rather shell-shocked at the scale of the destruction.
At first we found it difficult to get oriented in the landscape, so much had changed, but we began to look at how we could collect information to assess how the petrels would adapt to such major habitat change as fallen trees, landslips, and stripping of foliage. At that stage, in April, it was prior to the commencement of the bird’s breeding season. A visual inspection on 2 days in April showed that around 10% of nests in the main study colony had been directly affected – either the land they were on was missing (slipped away) or tree fall and erosion had made the burrows inaccessible. On the 2nd, smaller “Rowe” colony , there were windfall trees evident across the colony, but the number of burrows affected directly was low (only 1-2 at that stage were unusable by petrels).
Birds were present at night, some digging, others courting, but it was ‘business-as-usual’ for the birds with intact burrows. Many of the large trees that had fallen down created a visual barrier, (and were a bit of difficulty for us bipedal mammals to move around amongst) but the birds quickly adapted and found routes between the branches into their burrows where they remained intact. Aside from burrows where erosion had removed the soil completely it seemed only a small proportion were unusable, where large trees blocked the burrow entrance, or entrances were covered in soil or debris.
On a return visit in July, we found the burrows of the 150 or so petrel nests that we monitor regularly in the main colony, and systematically recorded the presence of the birds, burrow depth, and the ‘fate’ of the burrow. Using GoogleEarth, I’ve created polygons that show the area of the colony where we work, to show the areas affected by the storms. At each colony, the numbers of nests monitored were lower than the total number of burrows, or nests estimated present, as we only monitor burrows in certain parts of the colony, and where a pair has nested at least once since 2010.
At the large study colony, we located and confirmed the activity in all but 10 of the study burrows, from 91 total nests monitored and known to be active in 2013. However, around much of the colony’s lower edges, there were major landslips that had stripped away all top soil down to bedrock, with potential for these slips to cause further erosion over time.
At Rowe Colony, the losses were more substantial, with 27 of 64 burrows monitored having disappeared, become unusable, or likely to have been taken out by massive soil erosion, in areas that were too dangerous to traverse due to the land slips.
We found only one burrow in the zone there had been substantial soil movements in the April – July period, where birds were continuing to nest. They had a very tiny chick in July, in a burrow less than 50 cm in depth. Normally petrel burrows are over 1 m deep. This one was empty when we went back to band chicks in November, but this incident was the nest failure that we could attribute to the storm related adverse impacts on nesting outcomes. Many other nests were destroyed, and we couldn’t track what happened to the birds that would normally nest in those burrows. This less visible and more difficult-to-detect reduction in breeding output will take several years to uncover, if it is possible at all! However it may have had as great, or greater impact than one chick death on the overall growth of the population.
Its not clear whether the substantial damage that occurred at the Rowe colony occurred in the pre-breeding period (April) or subsequently. I did visit the colony in April, but didn’t notice this huge landslip that removed such an important part of the breeding colony. I am pretty confident that I would have seen this slip if it had been present in April. Heavy rains in late June or early July may have set it off at that stage, which would have possibly led to mortality of any birds incubating in the 25 or so burrows that we monitored in that area.
On the brighter side, breeding success was high for the birds that bred in 2014, with 60% of eggs at Rowe Colony having a fledgling in November (n=10 nests monitored) and 74% at Study Colony (n = 23 nests with eggs).
With two helpers, Jemma Hunt from DOC and Caroline Bost, we banded all chicks from study borrows in the study colony in November.
The young birds were really beautiful, very calm tempered, and it was a great pleasure to see them at this stage of development for the first time. They look just like the adults, except their feathers are glossy black, without any fading or wear that’s sometimes apparent on adult birds. The bills are very clean and pale grey. In adults they tend to be more weathered-looking. The chicks were mostly a stonking 1200-1500g, which bodes well for strong survival of these birds to breeding age.