Corticosterone responses of captive and wild northern brown kiwi (Apteryx mantelli) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Zoology at Massey University, Palmerston North, New Zealand
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Date
2000
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Massey University
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Abstract
Conservation strategies should work to mmnruse the occurrence of stressful
situations, which are likely to result in chronic elevations of corticosterone.
Consequently, identification of such situations would yield important information for
conservation management. The objective of this study was to compare the basal
levels of corticosterone and the corticosterone response of kiwi (Apteryx mantelli) in
different management systems. Repeated blood sampling enabled us to describe the
magnitude and duration of the corticosterone response, which is a measure of the
sensitivity of the hypothalamic-pituitary-adrenal (HP A) axis to stress. All kiwi
responded to capture and handling with a rise in plasma levels of corticosterone,
which peaked 30 min after capture. Corticosterone levels immediately after capture
in wild kiwi were significantly higher than those of captive kiwi. This was most
likely due to the method of capture, as wild kiwi took considerably longer to catch
than captive kiwi. The plasma level of corticosterone 30 min after capture in
nocturnal house kiwi was significantly lower than wild kiwi, but similar to those in
outdoor penned kiwi. The cause of these differences is unclear. Nocturnal house
kiwi may have become habituated to the presence of humans. Alternatively, it may
be due to nocturnal house kiwi being held on a different light cycle to outdoor pen
and wild kiwi. In addition, corticosterone levels in nocturnal house kiwi returned to
basal levels 2 h after capture and handling. There was no significant difference in
the binding affinity (I(I) and binding capacity (Bmax) of corticosteroid binding
globulin (CBG) between nocturnal house, outdoor pen and wild kiwi. Furthermore,
at no stage did maximum plasma levels of corticosterone exceed Bmax· Therefore,
the Bmax of kiwi CBG was not a major factor when interpreting corticosterone
responses of kiwi. Regularly handled kiwi do not respond to public display and
handling with an increase in plasma levels of corticosterone. Therefore, these kiwi
appear to have become habituated to this procedure. Elevated corticosterone levels
in wild kiwi immediately after capture indicate that determining the precise location
of wild kiwi is sufficient to induce a stress response. Therefore this practice should
be kept to a minimum. Low basal levels of corticosterone indicate that captive kiwi
have acclimatised to captivity. Furthermore, these results indicate that captive kiwi
are not exposed to chronic elevations in corticosterone.
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Keywords
Corticosterone, Brown kiwi, Apteryx mantelli, Stress