New Zealand Journal of Zoology abstracts
Heavy rimu (Dacrydium cupressinum) mast seeding and rat (Rattus
spp.) population eruptions on Stewart Island/Rakiura
Grant A. Harper
Zoology Department
University of Otago
P.O. Box 56
Dunedin, New Zealand
grant.harper@stonebow.otago.ac.nz
Abstract This study aimed to quantify changes in
rat abundance and population structure before, during, and after a rimu
(Dacrydium cupressinum) mast seed event in lowland forest on
Stewart Island, New Zealand. Rats, primarily ship rats (Rattus rattus),
were trapped in low numbers throughout the study period (March
2000–March 2003), except when they erupted to very high abundance in
spring 2002, shortly after heavy rimu seed fall. In the immediate
post-peak phase, scavenging of trapped rats increased substantially;
rats were seen and trapped in daylight; and weights of adult female
rats were low in relation to their size, which suggests that food
shortage was the cause of the subsequent steep decline in abundance.
Rat eruptions have been observed on Stewart Island after heavy rimu
seed fall several times over the past 40 years. Eruptions of rats
caused by heavy rimu seed-fall may have triggered the invasion of
nearby islands by rats, and caused the extinction of several native
species on Stewart Island.
Keywords Rattus rattus; ship rat; Rattus
norvegicus; Norway rat; seeding; Dacrydium cupressinum;
rimu; Stewart Island
Z04039; Received 11 November 2004; accepted 9 May 2005; Online
publication date 2 August 2005
New Zealand Journal of Zoology, 2005, Vol. 32: 155–162
0301–4223/05/3203–0155 © The Royal Society of New Zealand 2005
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