Lead exposure in free-ranging kea (Nestor notabilis), takahe (Porphyrio hochstetteri) and Australasian harriers (Circus approximans) in New Zealand : a thesis presented in partial fulfillment of the requirements for the degree of Masters of Veterinary Science in Wildlife Health at Massey University, Palmerston North, New Zealand
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2009
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Massey University
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Abstract
Lead is a highly toxic metal that has been used by humans for over 2000 years.
Over this time it has become increasingly apparent that despite its usefulness, lead is
one of the most highly toxic substances known to man. Current research into lead
exposure of humans focuses on low-level chronic exposure and its effects on learning
and behaviour. However, investigations into lead exposure of wildlife are still focussed
on mortalities, particularly of waterfowl and raptors, with little known about low-level
exposures or the effects on other species.
This study examines the exposure of free-ranging kea (Nestor notabilis) from
the Aoraki/ Mt Cook village and national park, takahe (Porphyrio hochstetteri) from
Tiritiri Matangi, Kapiti and Mana Islands, and the lead associated syndrome of
clenched-claw paralysis and leg paresis in harriers (Circus approximans) in New
Zealand.
Thirty-eight kea had detectable blood lead with concentrations ranging from
0.028 mg/L to 3.43 mg/L (mean = 0.428 mg/L ± 0.581). Analysis of tissue samples
found that seven of 15 birds died with elevated tissue lead. Lead exposure may be an
important contributing factor in kea mortality. As a result of these findings, lead
abatement in areas frequented by kea is being considered.
Eighteen of 45 takahe had detectable blood lead concentrations ranging from
0.015 mg/L to 0.148 mg/L (mean = 0.028 mg/L ± 0.042). Analysis of tissue samples
from offshore island and Murchison Mountains birds found that all had detectable lead.
Despite levels of lead exposure in the population being low and unlikely to result in
overt clinical signs, it is widespread and there may be significant exposure of birds
living around old buildings.
An investigation into the clinical signs, pathology and response to treatment of
clenched-claw paralysis and leg paresis in wild harriers was carried out. Harriers with
clenched feet had significantly higher blood lead concentrations than those without. In
conclusion, lead is a major factor in the expression of this clinical syndrome but other
factors not yet identified are playing a role.
This study demonstrates that lead is widespread in the New Zealand
environment exposing a diverse range of avifauna, and has made some progress towards
exploring some of its effects on health and survival.
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Kea, Takahe, Australasian harriers, Nestor notabilis, Porphyrio hochstetteri, Circus approximans, Epidemiology, Lead poisoning, Lead exposure