Birdwatching in Sydney

Visitors are always welcome at Cumberland Bird Observers' Club
with the Cumberland Bird Observers' Club

Gould's Petrels bounce back
Andrew being bitten by an adult Gould's Petrel.
Andrew being bitten by an adult Gould's Petrel.

In the early 1990's, Gould's Petrel numbered only about 200 nesting pairs, it's numbers were continuing to decline, it was producing very few offspring each year and it was only breeding at one location - Cabbage Tree island, near Port Stephens, NSW. The bird was in danger of becoming extinct.

However, the National Parks and Wildlife Service (NPWS), with the assistance of volunteers from the Cumberland Bird Observers' Club and others, have helped the birds so they now number about 700 pairs and regularly produce 300 chicks each summer. Although it is still Australia's rarest endemic seabird, it's future looks a lot better.

The Gould's Petrel is a diminutive member of the group of tube-nosed seabirds known as the Procellariiformes, which also includes albatrosses, shearwaters, fulmars and storm-petrels. It is 30cm in length and has a wing span of 75cm. The petrels breed on Cabbage Tree Island between October and May. Each pair lays only a single egg in a nest which is hidden among rocks and under fallen palm leaves. The young depart in March or April however it is not known exactly where the birds go once they leave the island. The young remain at sea for 3 years until they return to the exact spot where they hatched to search for a mate and a suitable nest site. Gould's Petrel may live for 30 years or more.

The rugged scenery on the eastern side of Cabbage Tree Island. Boondelbah Island is in the distance.
The rugged scenery on the eastern side of Cabbage Tree Island. Boondelbah Island is in the distance.

Banding studies from the 1950's to the 1980's indicated that the population of Gould's Petrel was in serious decline. In 1992 the NPWS initiated a comprehensive research program to identify the causes.

Two factors stood out - the fruit of the Bird-lime Tree and currawongs. Around the time that petrel chicks hatch, the Bird-lime Tree drops bundles of sticky fruit to the ground where they pose a threat to birds moving about the forest floor. The substance exuded by the fruit is so sticky that a single fruit can cause a petrel's wing to become hopelessly stuck to its body. Once incapacitated like this, the bird slowly dies of starvation or falls prey to scavenging birds.

NPWS ranger Nick Carlile banding a Gould's Petrel at one of the artificial nest boxes.
NPWS ranger Nick Carlile banding a Gould's Petrel at one of the artificial nest boxes.

Pied Currawongs however were an even more prevalent cause of mortality. These efficient predators were systematically searching the forest floor for petrels, chicks and eggs to feed to their own young.

Control measures were immediately put in place to remove the Bird-lime Trees from the breeding areas and reduce the currawong numbers. Immediately the breeding success of the petrels jumped from 20% to 55%. Although the immediate causes of petrel mortality were removed, the question remained as to why these unusual threats arose. The answer was rabbits.

Rabbits were introduced onto Cabbage Tree Island in 1906. They quickly denuded the island's vegetation resulting in the loss of the understorey. Without the understorey for concealment, nesting petrels are extremely vulnerable to attack by avian predators. The absence of any understorey also makes the petrels more vulnerable to entanglement in the fruits of the Bird-lime Tree because a thick understorey will capture most of the fruits before they get to the forest floor.

David reaching deep into a Gould's Petrel nesting hole - ouch!
David reaching deep into a Gould's Petrel nesting hole - ouch!

From 1997 to 1999 the NPWS undertook a rabbit eradication program. It was no easy task given the rugged terrain of the island however all rabbits have now been removed. The understorey is now regrowing and will in time provide the petrels with the protective covering they need.

The future for the Gould's Petrel is looking brighter now than it has for much of the last century. Indeed, with the removal of rabbits, the entire suite of natural ecosystems on Cabbage Tree Island are in far better shape than at any time in the recent past.

Constant vigilance however is still needed. A wild fire or the reckless introduction of exotic animals are constant threats. For this reason a second breeding population has been established on nearby Boondelbah Island and both islands are entirely off limits (except for NPWS staff and volunteers) with fines of $100,000 and two years' imprisonment.


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