Source: NZ Department of Conservation

Date:  15 September 2025

The Westland petrel/tāiko is one of only two species of seabird that exclusively breed on the mainland of New Zealand, which was once rich in seabird colonies. Habitat clearance and predation by introduced mammals have led to the almost complete disappearance of petrels from the North and South islands.

Department of Conservation Ranger Kate Simister, who leads a long-term study of the petrels, says decades of research has revealed the feisty seabird is holding its own but still has threats facing it.

Kate’s work involves monitoring the breeding attempts and success rates of hundreds of banded petrels to determine their rate of survival and population trend.

“They are incredible birds,” says Kate. “Decades of nest monitoring has shown they are not highly vulnerable to introduced predators, even as chicks. Their gutsy behaviour seems to have allowed them to continue breeding successfully on the mainland, unlike most other seabird species.”

“Their sass also means we must be careful when we are handing them – for their safety as well as ours – as even with leather gloves on, they can still draw blood.”

Tāiko pair up to raise one egg per season, which is laid in May, and incubated through to hatching in July. Their breeding success is typically high with about 70 per cent of breeding attempts each year yielding a chick that survives through fledging.

However, even with this breeding success and birds living to 40 years or more, the colony is only just maintaining its numbers. Tāiko are particularly slow breeders, first breeding at between five and ten years old, with many pairs choosing not to breed every year.

This year is particularly quiet with only around 35 per cent of birds breeding, says Kate. “We are working to learn more about the Westland petrels and understand why this is the case.”

The parents take turns incubating the egg while the other is out at sea searching for food. It is thought that it may be getting harder for the petrels to find food in some years, potentially due to more marine heatwaves, which may be having an impact on chick health.

If their mate’s return is significantly delayed, the hungry partner can abandon the egg and go in search of food, causing the egg to become cold and the developing chick to die.

One of the main impacts on the petrel population is fisheries bycatch mortality, as they are one of the most vulnerable species to bycatch in New Zealand. Light pollution is also a problem for the petrels, as they can get confused at night and crash land, injuring themselves in the process, getting run over by cars, or exposing themselves to predation.

DOC has been studying their movements and feeding behaviours at sea in recent years, to better understand their interaction with potential threats.

Naturing actions people can take to help seabird species like tāiko include buying sustainably caught fish and minimising individual contribution to global warming, which contributes to declining ocean health.

Over the last couple of years, this work has been supported by the Conservation Services Programme, which is partially funded by the fishing industry.

Background:
Conservation Services programme 

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