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.
| Identifer | oai:union.ndltd.org:ADTP/275833 |
| Date | January 2009 |
| Creators | Robertson, Louise Mary |
| Publisher | Massey University |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
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