Journal of the Royal Society of New Zealand abstracts
Establishment and extinction of a population of South Georgian diving
petrel (Pelecanoides georgicus) at Mason Bay, Stewart Island, New
Zealand, during the late Holocene
Richard N. Holdaway
Palaecol Research, P.O. Box 16 569, Christchurch, New Zealand.
Email: piopio@paradise.net.nz.
Martin D. Jones
Centre for Archaeological Research, University of Auckland,
Private Bag 92 019, Auckland, New Zealand.
Nancy R. Beavan Athfield
Rafter Laboratory, Institute of Geological and Nuclear Sciences,
P.O. Box 30 368, Lower Hutt, New Zealand.
Abstract A population of South Georgian diving petrels
(Pelecanoides georgicus) (c. 130 g) became extinct at Mason Bay, on
the west coast of Stewart Island, before European settlement. Pacific rat
(Rattus exulans) bones with the diving petrel fossils provided an
opportunity to determine whether the rats arrived before the petrels went
extinct. Fifteen 14C accelerator mass spectrometry (AMS) ages
on purified diving petrel bone gelatin from various parts of Mason Bay clustered
unexpectedly in the 14th and 15th centuries AD, and none was older. Bayesian
statistical analysis, using a Markov Chain Monte Carlo procedure, gave a
95% probability that the diving petrel colony was founded between 1338 and
1440 AD, lasted 40-310 years, and became extinct between 1475 and 1650 AD.
Possible reasons for the late colonisation of Mason Bay by South Georgian
diving petrels burrow are discussed. Bayesian analysis of five 14C
AMS determinations on Pacific rat bone gelatin did not exclude the possibility
that the Pacific rat arrived before the diving petrel colony was established.
However, the enriched δ13C of their bone gelatin suggests that
the rats had a partially marine diet, and a terrestrial calibration procedure
for their AMS ages was probably not appropriate. The Pacific rat is likely
to have arrived after the diving petrel colony became established and probably
caused the bird’s extinction after a short period of coexistence.
Keywords New Zealand; Stewart Island; extinction;
Pelecanoides georgicus; Rattus exulans; radiocarbon dating;
Bayesian statistics
R02034 Received 23 August 2002; accepted 22 May 2003; online publication
date 11 September 2003
© Journal of the Royal Society of New Zealand, Volume 33, Number
3, September 2003, pp 601-622
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