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Three species of the syngamid nematode Cyathostoma have been reported in raptors (Cyathostoma (Hovorkonema) variegatum, Cyathostoma americanum, Cyathostoma lari). These nematodes typically parasitise the respiratory tract (Lavoie and others 1999, Fernando and Barta 2008), air sacs (Hunter and others 1993) and the orbital and nasal cavities (Simpson and Harris 1992). To speciate Cyathostoma species, the copulatory bursa of adult males must be identified using light microscopy; however, if no males are present, then identification to genus level is only possible (Cyathostoma species) (Chitwood and Lichtenfels 1972). C americanum has been associated with diffuse pyogranulomatous air sacculitis, pneumonia and bronchitis (Lavoie and others 1999) and Cyathostoma (Hovorkonema) variegatum with thickened air sac walls and granulomatous lesions at sites of infection in raptors (Krone and Cooper 2002). Emaciation and anaemia have been reported in dead wild birds of prey in the winter months with Cyathostoma species infection, however, the authors considered the Cyathostoma species infections to be of limited importance, and that the observed emaciation and anaemia were likely a consequence of starvation (Simpson and Harris 1992). Infection of cyathostomes in free-living wild birds is believed in most cases to be of low prevalence and low intensity (Fernando and Barta 2008).
Numbers of breeding female hen harriers (Circus cyaneus) have declined by an estimated 20% in Britain during the last six years, and the hen harrier is now England's most threatened raptor species (Natural England 2008, Royal Society for the Protection of Birds 2011) on the UK Red List of Birds of Conservation Concern (Eaton and others 2009), and Section 41 of the UK Government's Natural Environment Research Council (NERC) list of species of critical importance in England. The hen harrier's current poor population status is primarily the result of continued human persecution (Natural England 2008). A …