Health and disease in Red-crowned Parakeets (Cyanoramphus novaezelandiae) on Tiritiri Matangi Island; causes of feather loss and implications for conservation managers
Jackson, Bethany (2014) Health and disease in Red-crowned Parakeets (Cyanoramphus novaezelandiae) on Tiritiri Matangi Island; causes of feather loss and implications for conservation managers. PhD thesis, Murdoch University.
Research into the diseases of free–ranging wildlife requires targeted surveillance for pathogen(s) of interest, however also relies on reference data of general health indicators against which findings can be interpreted. Wildlife reintroductions and translocations in New Zealand introduce specific disease risks related to spread of disease agents from the source site, exposure to novel disease at the destination, or changes in transmission factors for existing diseases at the destination. The discovery of Beak and feather disease virus (BFDV) causing clinical disease in wild Red-crowned Parakeets (RCP, Cyanoramphus novaezelandiae) intended for translocation in 2008 led to an increased interest from conservation managers in the pathogens affecting this species.
This study aimed to investigate health and disease in a free-ranging population of RCP experiencing feather loss, with an epidemiological focus to determine temporal trends in disease prevalence, and infer risk factors for disease expression. We captured 229 individuals over 5 sampling sessions between 2011-2013, including 4 surveys on Tiritiri Matangi Island (n=184), and one survey on Hauturu-o-Toi/Little Barrier Island (LBI) (n=45).
Normal haematological and biochemical reference ranges were described. The relatively high creatine kinase results highlighted a potential susceptibility to capture myopathy in this species, and warrant further investigation. Comparison of DNA-based sexing results to beak measurements demonstrated high concordance between the two sexing methods.
We investigated BFDV in the population by PCR of blood and feather, and found a low total prevalence on Tiritiri Matangi Island of 1.09% (0.1-3.9%) for 2011-12, and on Hauturu-o-Toi/LBI of 4.4% (0.5%-15.1%) in 2013. Screening by PCR of opportunistic samples from the Wellington region of the North Island, and phylogenetic analysis of the full viral genome sequences from all positive samples, revealed ongoing evidence of viral flow between RCP and Eastern Rosellas (Platycercus eximius) in the Hauraki Gulf/Auckland region, with separate but closely related strains from the Wellington region. These findings, combined with the first report of seroprevalence data for a New Zealand parrot using the haemagglutination inhibition test, suggest RCP may be a dead-end or spill over host for BFDV, with implications for a downgrading of the conservation threat this pathogen currently poses.
The collection of skin biopsies in all birds during the 2012 and 2013 (n=135) following an outbreak of feather loss led to the discovery of a knemidokoptinid mite associated with mange in this species. The mite, Procnemidocoptes janssensi has only been previously described once from a lovebird (Agapornis nigrigenis) in Zambia in 1967. We present the first report of the mite in New Zealand, including histopathological stages of infestation, and the first epidemiological study on mange in a wild parrot globally. Relative mite abundance (number of mites per skin biopsy) was found to be associated with likelihood of feather loss and clinical signs. Findings were also consistent with the presence of a carrier or endemic state, with emergence of clinical disease and epizootics triggered by as yet unknown host, environment or mite factors.
Finally, we conducted a nesting study using natural and artificial nests on Tiritiri Matangi Island from 2012-2013, to infer disease risks for nestling and fledgling RCP, and describe baseline health parameters for this group. Overall nesting success was low, and likely to be related to the drought experienced that year. Nest mites were detected in 64% (95%CI: 41-83%) of nests, however their presence did not significantly affect fledging success or numbers. Chicks from nest mite positive nests had higher mean absolute heterophil counts (p=0.04), suggesting an inflammatory response to the presence of these mites, and a potential fitness cost that warrants further study. We did not detect BFDV in any nests studied, and therefore cannot infer the impact of this pathogen on this age class, although the study provided further evidence BFDV is present at a low prevalence on Tiritiri Matangi Island.
|Publication Type:||Thesis (PhD)|
|Murdoch Affiliation:||School of Veterinary and Life Sciences|
|Supervisor:||Warren, Kristin, Jakob-Hoff, Richard, Varsani, Arvind, Holyoake, Carly and Robertson, Ian|
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