New Zealand Journal of Zoology abstracts
Tuatara (Sphenodon punctatus) feeding ecology in the presence of
kiore (Rattus exulans)
GRAHAM T. USSHER
School of Environmental and Marine Sciences
University of Auckland
Private Bag 92019
Auckland, New Zealand
email: g.ussher@auckland.ac.nz
Abstract The diet of tuatara was investigated on
kiore-inhabited Lady Alice Island in the Hen and Chickens Group, northern New
Zealand, between 1993 and 1994. Both dietary (targeted) and inedible
(incidental) items were eaten by tuatara. Dietary items recorded were
exclusively invertebrate in origin. Estimates of environmental availability of
invertebrates and indicated that the prey consumed were strongly selected by
size and by taxa. Beetles, insect larvae, arachnids and weta comprised the
greatest proportion of total diet, appeared in the greatest number of stomachs
and were taken in excess of their abundance. Most prey were >10 mm in
length, despite an abundance of smaller prey in the environment. The risk of
predation by tuatara was greatest for terrestrial invertebrates and least for
arboreal species. The composition of diets by habitat was largely similar
between mid-successional kanuka (
Kunzea ericoides) and late successional
mixed broadleaf forest. The size distribution of prey eaten by tuatara in
kanuka habitat during autumn, and the low number of tuatara yielding dietary
samples, are discussed in terms of food competition with kiore. Overall, the
foraging behaviour of tuatara was not obviously different on rodent-free
compared to kiore-inhabited islands, either indicating that food competition is
insufficient to influence diet, or that tuatara are unable to change their
feeding behaviour under a higher degree of competitive pressure for prey items.
Clear support for either hypothesis is lacking.
Keywords dietary analysis; feeding ecology; tuatara;
Sphenodon punctatus; kiore; Rattus exulans
Z98019
Received 12 May 1998, accepted 17 November 1998
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