Anthelmintic treatment and digestive organ morphology of captive-reared kaki (Himantopus novaezelandiae) released to the wild : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Conservation Biology at Massey University, Palmerston North, New Zealand
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Date
2009
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Massey University
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Abstract
The continued existence of New Zealand’s critically endangered and endemic black stilt or kakï
(Himantopus novaezelandiae) relies on an intensive captive management programme. While this is
successful at rearing large numbers of birds for release to the wild, poor survivability of these birds
is limiting significant increases in the wild population. Predation and starvation are suspected to
be the most common causes of death in released birds, but underlying contributing factors to these
mortalities have not been fully evaluated. This research investigates the possible contribution of
gastrointestinal (GI) helminth burdens and suboptimal digestive organ development to the high
mortality rates of released kakï. Emphasis is placed on evaluating the methods used to assess the
importance of these factors and to make informed recommendations for future management.
The efficacy of the anthelmintic regime used for kakï was assessed by dosing half of the 80 captive
birds with praziquantel (PZQ) prior to release in 2007. Faecal samples were collected before and
after anthelmintic treatment, and before and after release to the wild. Post mortem worm counts
were conducted on 11 birds that died following release and historical worm count records dating
back to 1997 were accessed. The main findings were: PZQ had high efficacy against trematodes;
treatment did not prevent re-infection; birds were exposed to helminths at release site; and there
was no advantage of treatment for survival. Overall, the results suggest that anthelmintic treatment
is an unnecessary cost. Consequently, recommendations were made to cease anthelmintic
treatment or reduce its intensity, continue health screening, and incorporate annual efficacy testing
to monitor the emergence of anthelmintic resistance.
The reliability of faecal screening for GI helminths was evaluated. Faecal egg counts (FECs) were
found to be poor indicators of worm burden. The two modified sedimentation methods used to
detect trematodes provided relatively low egg recovery rates. Trematode egg shedding varied
between days but not by hour of the day or temperature. The collection and analysis of pooled
faecal samples proved to be more cost and time-effective than samples from individual birds and
the larger masses collected resulted in greater sensitivity. In conclusion, faecal analysis of pooled
samples is a useful qualitative indicator of helminth presence or absence but is quantitatively
unreliable.
In order to assess the importance of digestive organ development to captive-reared and released
kak?, the digestive organs of healthy and emaciated captive, released and wild Himantopus sp.
were compared. Captive and released kak? had generally smaller digestive organs than wild birds,
released birds did not increase digestive organ size to match the high fibre wild diet, and emaciated
birds did not have atrophied organs. However, the greatest mortality rates occur soon after release,
while the birds were still being supplementary fed. These results suggest that reduced digestive
efficiency is probably not contributing significantly to mortality rates and the direct impacts of the
translocation are probably greater risk factors. The continued provision of supplementary food to
released birds and an increased focus on habitat enhancement and predator control at release sites
were recommended. The reliability of comparing fresh and formalin fixed Himantopus sp. gut
specimens was evaluated. Significant differences in fresh and formalin fixed organ dry masses and
variation in preserved organ lengths indicate that this variation should be considered in future
studies.
In conclusion, current management practices appear to be successful in ensuring that GI helminths
and reduced digestive efficiency do not significantly lower the survivorship of captive-reared and
released kakï. There is a need for further research into developing a more direct physiological
assessment of the impacts of GI helminths and gut morphology as well as considering the role that
starvation may have on poor survivability.
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Keywords
Black stilt, Captive management, Endangered species, Gastrointestinal helminth