 Steve N G Howell
The Critically Endangered Magenta Petrel is one of the world’s rarest seabirds
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Critically Endangered seabird losing its pulling power
23-04-2008
A study into one of the world’s rarest seabirds provides knowledge that could help avoid extinction. Molecular analysis of the Critically Endangered Magenta Petrel Pterodroma magentae (also known as the Chatham Island Taiko) discovered that 95% of non-breeding adults were male. This suggests that critically low population levels may be causing male birds difficulty in attracting a mate. Their calls are too spread out to attract the infrequent females which pass by. Conservationists are planning to increase the male Magenta Petrel’s pulling power by creating a new breeding colony within a predator-proof fence.
Magenta Petrel was rediscovered in 1978 on Chatham Island, New Zealand, 111 years after it was first collected at sea. The species has undergone an estimated historical decline of 80% over 45 years. The primary cause is introduced species – such as pigs, cats, Weka and rodents - which predate the petrels and compete for their nesting burrows. There are now thought to be between 8 and 15 breeding pairs left in the world.
Male and female Magenta Petrels look extremely similar, and are difficult to distinguish by sight alone. Scientists collected blood samples from almost the entire known living population over a 20 year period. This allowed the team to distinguish gender accurately using DNA sexing techniques.
“It has been found in other petrel species – such as Manx Shearwater, Cory’s Shearwater, and Wandering Albatross - that males return most frequently to the site where they were reared as a chick” —Ben Lascelles, BirdLife’s Marine IBA Research Assistant
The sex-ratio of males to females was approximately even in petrel chicks and breeding adults. However, 95% of non-breeding birds were found to be male. This finding suggests that unpaired males may be having difficulty in attracting females to burrows.
Conservationists are helping to increase the petrel’s density by focusing birds within the Sweetwater Secure Breeding Site. This is being achieved by translocating chicks, and by using calls to attract adult petrels to the refuge. Eight chicks were successfully moved and fledged last year, and The Chatham Island Taiko Trust was established in 1998 to provide legal status to the continuing work.
Scientists are hoping to use knowledge of male behaviour traits to make the plan work. “It has been found in other petrel species – such as Manx Shearwater Puffinus puffinus, Cory’s Shearwater Calonectris diomedea, and Wandering Albatross Diomedea exulans - that males return most frequently to the site where they were reared as a chick”, commented Ben Lascelles BirdLife’s Marine IBA Research Assistant. By using the DNA sexing technique to slightly favour male chicks for translocation, the team hope to increase the numbers of birds returning as adult breeders to the refuge.
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