High prevalence of Leucocytozoon spp. in the endangered yellow-eyed penguin (Megadyptes antipodes) in the sub-Antarctic regions of New Zealand L. S. ARGILLA† , L. HOWE, B. D. GARTRELL* and M. R. ALLEY New Zealand Wildlife Health Centre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand (Received 12 July 2012; revised 14 October 2012; accepted 8 November 2012; first published online 29 January 2013) SUMMARY Yellow-eyed penguins (YEPs) have suffered major population declines over the past 30 years, with no single cause established. Leucocytozoon was first identified in yellow-eyed penguins in 2005. During the 2008/09 breeding season, a high mortality was seen in both mainland yellow-eyed penguins as well as those on Enderby Island of the Auckland Islands archipelago. A high overall prevalence of Leucocytozoon spp. in association with a high incidence of chick mortality was observed during this period on Enderby Island. One chick had histological evidence of leucocytozoonosis with megaloschizonts in multiple organs throughout its body. In addition, a high prevalence (73·7%) of Leucocytozoon was observed by PCR in the blood of adult Enderby yellow-eyed penguins taken during the 2006/07 season. These findings were different from the low prevalence detected by PCR on the coast of the South Island (11%) during the 2008/2009 breeding session and earlier on Campbell Island (21%) during the 2006/2007 breeding session. The Leucocytozoon spp. sequences detected lead us to conclude that the Leucocytozoon parasite is common in yellow-eyed penguins and has a higher prevalence in penguins from Enderby Island than those from Campbell Island and the mainland of New Zealand. The Enderby Island yellow-eyed penguins are infected with a Leucocytozoon spp. that is genetically distinct from that found in other yellow-eyed penguin populations. The role of Leucocytozoon in the high levels of chick mortality in the yellow-eyed penguins remains unclear. Key words: Leucocytozoon, yellow-eyed penguin, Enderby Island, mortality, New Zealand. INTRODUCTION The yellow-eyed penguin (Megadyptes antipodes), or Hoiho, is endemic to New Zealand and is one of the rarest species of penguin (McKinlay, 2001). It is the only member of its genus and one of the most endangered of the 18 species of penguins. The yellow-eyed penguin (YEP) has been classified as endangered on the IUCN Red List since 2000 based on extreme population fluctuations, restricted breed- ing range and declines in quality and quantity of their natural habitat (Birdlife International, 2011). The population is estimated at between 6000 and 7000 birds (McKinlay, 2001), with 630 pairs on the South Island southeast coast, 178 pairs on Stewart Island, 520–570 pairs on the Auckland Islands and around 405 pairs on Campbell Island (Moore, 1992; McKinlay, 2001). Unlike other penguin species, YEPs are not colonial but instead nest in sparse colonies and avoid visual contact between pairs at adjacent nest sites. Approximately two-thirds of the entire population of YEPs is found on the southern offshore and sub-Antarctic islands of New Zealand with 22% on Campbell Island (52°32′ 24″S, 169°8′ 42″E), 23% on the Auckland Island archipelago (50°42′0″S, 166°5′0″E) and 21% found on Stewart (47°00′0″S, 167°50′0″E) and Codfish (46°47′0″S, 167°38′0″E) Islands (Darby and Seddon, 1990; Moore, 1992). The remainder of the population is found on the east coast of the South Island between South Otago and Banks Peninsula, with 3 main colonies located at Oamaru, the Otago Peninsula and the Catlins (Darby and Seddon, 1990). Recent periodic mass mortality events or popu- lation declines have been documented in YEPs on the South and Stewart Islands since the 1980s, resulting in significant population declines (Moore et al. 2001). These population declines have been attributed to non-infectious events such as unidentified phyto- toxins (Gill and Darby, 1993), starvation, poor nutrition (Vanheezik, 1990a; Vanheezik and Davis, 1990) and a possible relationship with climatic events such as El Nino or the Southern Oscillation (Moore and Wakelin, 1997). Infectious causes of population decline have also been identified, in particular avian haemoparasites, such as Plasmodium and more * Corresponding author: New Zealand Wildlife Health Centre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Private Bag 11 222, Palmerston North, New Zealand. Tel: 011 64 6 356 9099. Fax: 011 64 6 350 5714. E-mail: B.Gartrell@massey.ac.nz † Current address: Wellington Zoo, Newtown, Wellington, New Zealand. 672 Parasitology (2013), 140, 672–682. © Cambridge University Press 2013 doi:10.1017/S0031182012002089