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Nestling mortality in a translocated population of hihi/stitchbirds (Notiomystis cincta) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Conservation Biology at Massey University, Palmerston North, New Zealand
Nestling mortality in a reintroduced population of the endangered and endemic hihi/stitchbird (Notiomystis cincta) was investigated over one breeding season (2008-09) at Zealandia – Karori Sanctuary, New Zealand, to determine whether disease impacted on nestling survival. High rates of both hatching failure (56%) and nestling mortality (39%) in the first clutch made this the least successful breeding season since translocation in 2005. Overall 34% of eggs survived to fledge, compared to 52% and 58% in 2005-06 and 2006-07 respectively. Samples collected from 34 live and 25 dead nestlings were screened for evidence of disease. Bacterial and fungal pathogens were isolated from gastrointestinal swabs but there was no evidence of coccidia or other intestinal parasites in faecal samples. There was no evidence of significant abnormalities in the blood collected from hihi prior to fledging in the haematological parameters tested, and all blood samples were negative for malarial parasites. Tropical fowl mites (Ornithonyssus bursa) were found on nestlings and recovered from nest material in very small numbers. Sixty percent of nestling mortality occurred during the first 7 days of life, most often caused by starvation (16%) or poor pulmonary aeration (20%), and death was associated with seasonally low minimum daily temperatures below 11oC. Two older nestlings that died suffered from aspergillosis and an unidentified haemoparasite respectively. Seven nestlings (28%) aged 6-19 days died as a consequence of ventriculitis due to traumatic penetration by insect remnants identified as bee or wasp stings (Hymenoptera). The resulting granulomatous lesions were found in the gizzard mucosa, muscle layers and ventricular or intestinal serosa, and were associated with bacterial and/or yeast secondary infection. It was concluded that hihi may lack the evolutionary adaptations to safely consume introduced bees (Apis mellifera) and wasps (Vespula germanica, V. vulgaris) that are attracted to the feeding stations used to support reintroduced hihi populations. Histopathological examination showed candidiasis contributed to the deaths of four nestlings and Candida albicans was isolated from the gastrointestinal swabs of 13 live nestlings from four nest sites, eight of which survived to fledge. The potential of all pathogens may be increased by any cause of temporary or permanent immunosuppression and, in this establishing population, the majority of nestling deaths were associated with environmental conditions (temperature) and ecological factors (introduced prey). It is suggested that ongoing monitoring should include use of temperature data-loggers in hihi nest boxes, health screening of live nestlings, necropsy examination of dead birds, and spore counts to determine environmental levels of Aspergillus. Nest box insulation and/or heating could reduce the incidence of hypothermia in nestlings. A review of the carbohydrate provisioning protocols may reduce bee/wasp numbers and minimise the effect of Candida albicans at this site.