TOSSI – Nurture vs nature

By Ngaire Wallen & James Ross

We were thrilled that grey-faced petrel reared six chicks at Tawharanui last year – three were in nest boxes installed to improve breeding opportunities for seabirds. While not threatened, grey-faced petrel and other seabirds once bred in enormous numbers on the mainland of New Zealand and played a crucial role in the formation of our fertile soils.

Because of the density of the original seabird population – before people, rats, stoats, cats and dogs arrived and ruined their breeding habitat – the poo dropped on the forests as they returned from days at sea provided essential nutrients that fed the trees that protected the birds and housed the lizards and so on. You might say our verdant forest landscape was based on seabird evacuations.

The significant benefit our seabirds have on habitat is something that we are keen to reinstate at Tawharanui so we have installed solar-powered bird callers and nest boxes and have made considerable progress towards restoring colonies of grey-faced petrel, fluttering shearwater and diving petrels. In May this year, we were surprised to find one of the nest boxes occupied by a pair of little penguin – also known as little blue penguins or korora – a threatened species in New Zealand.

Conventional wisdom suggested that the much larger petrels would see them off. We were shocked to find a dead grey-faced petrel with nasty head injuries in the nest box the following week. Even worse was to follow when we later found a second dead petrel with similar injuries at the entrance to the box. There was obviously some alarm when the dead birds were found. One bird was identified by its leg band as having previously bred at Tawharanui. Could penguins really have done this or was there a more sinister scenario? Investigations were made. Questions asked. Game cameras, tracking tunnels and rat traps installed and one bird was sent to Massey University for an autopsy. And the outcome?

Little penguins, those cute and much loved creatures, have a dark side. Approach with caution! Having set up home in the nest box, all evidence points to them literally pecking the petrels to death.

Such is the challenge of conservation projects; unintended consequences that in themselves are good can have a negative outcome for another species. Last year we were delighted to find a little penguin nest in the same vicinity as the seabird nest box sites. We didn’t anticipate penguins occupying a nest box, with fatal consequences. We can nurture species and keep them safe from predators, it seems, but not from nature. There is a good outcome, of course. The penguin pair are incubating an egg and we have several grey-faced petrels on eggs in nest boxes and natural burrows nearby.

Meanwhile, we have completed another very successful planting season, with over 20,000 plants now growing on former pasture-land. The area that we have been planting over the last three seasons is home to some of our takahe. A pair of one of the rarest birds in the world were happily bumbling about in the young growth just a couple of hundred metres away from where the public were planting. As always, our grateful thanks to everyone who came to help and who contributed to the revegetation of Tawharanui Open Sanctuary.

The next TOSSI workday will be Sunday September 6, followed by the Toss annual general meeting after lunch.