Investigation of an outbreak of craniofacial deformity in yellow-eyed penguin (Megadyptes antipodes) chicks

Abstract

AIM: To investigate an outbreak of severe craniofacial deformity in yellow-eyed penguin (Megadyptes antipodes, hōiho) chicks at a single breeding site on the Otago Peninsula in the South Island of New Zealand.

METHODS: Morbidity and mortality of yellow-eyed penguins breeding on the coastal regions of Otago was monitored from November 2008 to March 2009. Dead chicks and unhatched eggs were recovered and examined. Between October and December 2008 32 eggs were recorded at 17 nests in the Okia Reserve. Eleven chicks survived to about 90 days of age, of which eight were found to have moderate to severe craniofacial deformity. The six most severe chicks were subject to euthanasia and examined in detail at necropsy, and the remaining two affected chicks were released to the wild after a period of care in a rehabilitation centre. Post-mortem samples were analysed for inorganic and organic toxins.

RESULTS: The six deformed chicks all had severe shortening of the mandible and maxilla by 20−50 mm. The rostral and caudal regions of the skull were approximately 40 and 80% of normal length, respectively. Other, more variable lesions included crossbill deformity, malformed bill keratin, microphthalmia with misshapen scleral ossicles and oral soft tissue excess thought to be secondary to bony malformations. During the same year, mild sporadic bill deformities were also reported in 10 unrelated chicks from >167 chicks at other breeding sites on the southern Otago coast. Concentrations of organic toxins and heavy metals in body tissues from affected chicks were apparently similar to those in unaffected chicks on other beaches.

CONCLUSIONS: No cause of this outbreak of craniofacial deformity could be established although the high prevalence at a single site suggests that it was due to an unidentified local teratogen.

GRAPHICAL ABSTRACT

KEY WORDS:

• Yellow-eyed penguin
• crossbill deformity
• congenital malformation
• teratogen

Acknowledgements

We thank the Coastal Otago Area Office of the Department of Conservation, Yellow-eyed Penguin Trust, St. Kilda Vets, Dunedin City Council, and the whanau of Teone Wiwi Taiaroa for their assistance and cooperation with this investigation. Andrew Lonie (Otago Conservancy, DOC) provided Figures 1 and 2. Janelle Ward and Ellen Schoener assisted with some of the necropsies.

Notes

¹J.T. Darby, retired from Otago Museum, Dunedin, New Zealand.