Investigation of a mortality cluster in wild adult yellow-eyed penguins (Megadyptes antipodes) at Otago Peninsula, New Zealand

We investigated an epidemic mortality cluster of yellow-eyed penguins (Megadyptes antipodes) that involved 67 moribund or dead birds found on various beaches of the Otago Peninsula, New Zealand, between January 21 and March 20, 2013. Twenty four carcases were examined postmortem. Histological lesions of pulmonary, hepatic and splenic erythrophagocytosis and haemosiderosis were found in the 23 of 24 birds. Fifteen birds also had what appeared to be haemoglobin within renal tubular epithelial cells. Despite consistent histological lesions, a cause of death could not be established. Virology, bacteriology and molecular tests for avian influenza and avian paramyxovirus-1, avipoxvirus, Chlamydia psittaci, Plasmodium spp, Babesia spp, Leucocytozoon spp, and Toxoplasma gondii were negative. Tissue concentrations of a range of heavy metals (n = 4 birds) were consistent with low level exposure, while examination of proventricular contents and mucus failed to detect any marine biotoxins or Clostridium botulinum toxin. Hepatic concentrations of total polycyclic aromatic hydrocarbon (PAHs) (n = 5 birds) were similar to background concentrations of PAHs previously found in yellow-eyed penguins from the South Island of New Zealand. However there were significantly higher concentrations of 1-methylnapthelene and 2-methylnapthelene. The biological significance of this finding is unclear. A temporal investigation of the epidemic did not indicate either a common source or propagative epidemic pattern. Although our investigation did not definitively implicate a toxic or infectious agent, the results identified possible causes that should be investigated further in the event of future mortality clusters.