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Dr Ray Pierce, ecologist, pictured right banding a Pycroft’s Peterel on Lady Alice Island (Hen and Chickens group), writes the third in a series of articles on conservation at Whangarei Heads:
Before the arrival of people and their animals in New Zealand, huge colonies of seabirds numbering in the millions of birds existed on the mainland and offshore islands. Penguins and several species of petrels and shearwaters occupied coastal headlands like Bream Head where the hillsides were festooned with their burrow.
Every sheltered crevice would have provided a potential nest site. Their burrows were often shared with kiwi, tuatara, large lizards and sometimes other seabird species.
The air around the colonies would have been distinctively pungent, the uric acid droppings providing an important nutrient boost for the plants of the forest, with species like Peperomia, parapara and puka doing well in nutrient-rich areas around the bird colonies.
Nutrients from the land generally end up being washed into the ocean, but seabirds are one of the few animal groups that transport nutrients (particularly compounds of nitrogen and phosporus) from the ocean back to the land.
Today, the large mainland seabird colonies have long since disappeared and only a few hardy penguins (korora) and grey-faced petrels (oi) hang on tenuously at Bream Head, the rest having been eaten by mammalian predators or their burrows collapsed by livestock.
The loss of these seabirds has seen the demise of nutrient cycling, with the growth rates and health of seedlings and mature plants compromised. The restoration of both the seabird populations and the ecological processes requires the removal and exclusion of predators, i.e. trapping and poisoning predators to extinction and fencing them out.
It is not good enough to have a few rats, hedgehogs or mustelids hanging on at Bream Head, because these predators will keep plundering the eggs of any birds attempting to recolonise, or they may even kill the adult birds themselves.
Once the predators have gone, some species of seabird, like the oi and korora, will recover naturally and it is possible that some others will recolonise the area too. There have been many sightings of other seabirds (dead or alive) in the bush at Bream Head, including for example such rarities as the Pycroft' petrel, which currently breeds mainly at the Hen and Chickens and Mercury Islands.
The playing of tapes of selected species at the right time of year (i.e. during mating and burrow excavation periods) may entice more of these birds to the predator-free site. Other petrels and shearwaters may need to be transferred as fledglings (youngsters) from offshore islands like the Hen and Chickens and Poor Knights. By placing them in artificial burrows at Bream Head and providing a meal or two before they leave to go to sea, these birds will become imprinted locally and return to the area as mature adults.
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