Efficacy of anthelmintic treatment in captive-reared black stilts (Himantopus novaezelandiae) released to the wild

Abstract

AIMS: To assess the efficacy of praziquantel (PZQ) administered to control helminths in captive-reared critically endangered black stilts (Himantopus novaezelandiae) before their release into the wild and determine the effect on their survival shortly after release.

METHODS: Of 77 captive black stilts, 37 were treated with PZQ prior to release into the wild in South Canterbury, New Zealand, in August and September 2007. Faecal helminth egg counts (FEC) were measured before and after anthelmintic treatment, and before and after release to the wild using modified faecal flotation and sedimentation methods. In addition, total helminth counts were determined in 11 of the birds that died following release, as well as four captive and 11 other wild stilts.

RESULTS: The efficacy of PZQ against trematodes was 92% and against Capillaria spp. was 34%. No trematode or Capillaria spp. eggs were detected in treated birds 1 day after treatment, but FEC increased 3–5 days after treatment. There were no differences in the total helminth counts for trematodes, cestodes or Capillaria spp. in control or treated birds (p>0.2). Survival did not differ between treatment groups in the August or September releases (p>0.4). Of control and treated birds, 11/17 (65%) and 8/14 (57%) survived to 31 days, respectively, in the August release, and 16/20 (80%) and 10/15 (67%) survived to 84 days, respectively, in the September release.

CONCLUSION: Overall, the results suggest that PZQ treatment may be an unnecessary cost and the risks of producing anthelmintic resistance, injuring the birds during processing or producing an unnecessary stress response at the time of release could exceed any likely benefits.

CLINICAL RELEVANCE: It is recommended that pre-release anthelmintic treatment of black stilts should be used only if indicated by health screening. Any treatment should incorporate annual efficacy testing to monitor the emergence of anthelmintic resistance.

KEY WORDS:

• Captive breeding
• Himantopus novaezelandiae
• faecal egg counts
• gastrointestinal helminths
• release survival

Acknowledgements

We thank R. Maloney, Department of Conservation, for his support throughout our research and for providing useful feedback on the proposal. We are also grateful for the field assistance provided by the Twizel Department of Conservation team, especially J. Hiscock, D. Murray, I. Andrews, L. Hastie and M. Fairhall. J. Salinsky and E. Schoener from Massey University also assisted with field work. We thank B. Adlington, A. Tunnicliffe, I. Scott, W. Pomroy, A. Robertson and S. van Herpt for technical advice and assistance in the lab. K. Seymour created the map of the study area.

Notes

1 J. Hiscock, DOC, Twizel, New Zealand.

Additional information

Funding

This research was funded by grants from the Association of Avian Veterinarians and the IVABS Student Research Fund. L. Robertson was supported by a Manawatu branch of the New Zealand Federation of Graduate Women Scholarship, a Phyllis Irene Grey Fellowship in Veterinary Science and the Golden Plover Award.