The impact of isolation from mammalian predators on the anti-predator behaviours of the North Island robin (Petroica longipes) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Conservation Biology at Massey University, Auckland, New Zealand
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Date
2009
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Massey University
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Abstract
Conservation in New Zealand has begun to focus heavily on the restoration of
degraded mainland ecosystems and the reintroduction of native species that have become
locally extinct. In many cases the individuals that are selected for reintroduction are
harvested from ‘mammal-free’ offshore islands. This thesis examines the effects of
isolation from mammalian predators on the predator avoidance behaviours and predator
recognition abilities of New Zealand birds using the North Island robin as a model. It
also investigates whether any effects of isolation from mammalian predators has a lasting
impact on mainland populations founded by individuals from offshore islands.
Nest site selection behaviours were compared across three populations that are
exposed to different suites of predators and have differing translocation histories;
Benneydale, Tiritiri Matangi and Wenderholm. Point height intercept and point-centred
quarter surveys were used to compare habitat availability between the sites and to
compare nest sites with the available habitat. Eight nest characteristic variables were also
compared across the three sites using a principle component analysis. Benneydale nests
were located higher in the trees and were more concealed than nests at the other two sites.
Nests on Tiritiri Matangi were supported by large numbers of thin branches and were
located toward the periphery of the nest tree. Unfortunately these differences are very
difficult to interpret due to a high degree of variation in the habitat types present at the
three sites.
The anti-predator behaviours initiated in response to a model stoat, model
morepork and control were used to test the ability of nesting robins to recognise the threat
that each of these treatments might pose to nest success. Behavioural variables were compared between Benneydale, Tiritiri Matangi and Wenderholm using a response
intensity scoring system and a principle component analysis. The results indicated that
isolation from mammalian predators on Tiritiri Matangi has suppressed the ability of
robins on the island to recognise the predatory threat posed by a stoat. They also suggest
that the intense mammal control carried out at Wenderholm may have inhibited the
ability of local robins to produce strong anti-predator responses when faced with a stoat.
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Keywords
Predator recognition, Predatory threats, Island bird sanctuaries