Feather loss in Adélie penguins
Adélie penguin at Cape Bird, Ross Island showing feather loss on its back. Image - Wray Grimaldi
Landcare Research (and previously the Department of Scientific and Industrial Research) has been studying Adélie penguin colonies on Ross Island in Antarctica since the 1980s. Population sizes are currently healthy; however in the austral summer of 2011–12, an abnormal feather loss condition was observed for the first time at the Cape Bird and Cape Crozier colonies, affecting approximately 1 in 1000 birds.
Such feather loss has been observed previously on rare occasions in African penguin chicks in Africa, Adélie penguins in East Antarctica, king penguins on Possession Island, Magellanic penguin chicks in South America, and rockhopper penguins on the Falkland Islands, with malnutrition, lice infestation and ticks being identified as possible but unproven causes (aetiology).
With one key role of feathers being to provide birds with insulation, abnormal feather loss is likely to threaten survival of affected penguins. Hence, understanding its cause(s) is important, particularly since the paucity of prior records of abnormal feather loss in penguins suggests it could be an emerging disease. With this in mind, Melanie Massaro (United States Antarctic Program) (USAP) and colleagues collected biomedical samples from 30 adult Adélie penguins exhibiting abnormal feather loss and 30 adults without obvious signs of feather loss in January 2012. Penguins were caught using long-handled nets as they returned from foraging at sea and before they reached their nesting sites. The birds were examined for abnormalities, such as wounds and external parasites, before blood samples and cloacal swabs were collected. Feather samples from Adélie penguins at Cape Bird were also taken from the border of areas of feather loss on affected birds by University of Otago PhD student Wray Grimaldi. The collected material was returned to New Zealand and, under the supervision of Dan Tompkins (Landcare Research), subjected to a range of tests.
Affected birds had bare patches of skin on parts of the body otherwise normally feathered. However, the underlying skin appeared normal and no external parasites were observed. Likewise, the feathers collected looked normal when examined by scanning electron microscopy, and no ectoparasites or fungal elements were observed. An examination of thin blood smears on slides failed to show any blood parasites, but birds showing feather loss had higher proportions of lymphocytes and basophils and lower proportions of heterophils than birds showing no loss of feathers. These differences in white blood cell counts could suggest a viral aetiology - viral infection is one cause of raised counts of lymphocytes while raised counts of basophils have been associated with skin disorders in mice and humans.
To further investigate a potentially viral aetiology, pooled cloacal swabs from both birds with feather loss and those without it were subjected to metagenomic viral pathogen discovery (see article by Dan White in this issue for brief details of this technique). The sequence data produced showed evidence of three putative (supposed) new enteric penguin viruses, showing similarity to rotaviruses, turkey hepatitis viruses and astroviruses, respectively. Of the three penguin viruses, only the putative astrovirus was detected solely in the sample pool from birds exhibiting feather loss. (The putative rotavirus was detected in birds exhibiting feather loss and in those unaffected (to a much lesser extent), while the putative turkey hepatitis virus was only detected in the sample pool from birds without signs of feather loss.) Astroviruses and rotaviruses have been isolated from poultry, both in healthy and sick flocks, though no reports associate either of these viruses with feather loss. Follow-up work is recommended to investigate whether the novel astrovirus detected in Adélie penguins is causing the observed feather loss condition.
This work was supported by MBIE Funding to Landcare Research, and a University of Otago Postgraduate scholarship to Wray Grimaldi. Logistics were funded by Antarctica New Zealand and United States Antarctic Program.