Parasite control and breeding success in pheasants (Phasianus colchicus).

Abstract

In Great Britain approximately 25 million hand-reared pheasants Phasianus colchicus are released in summer each year to increase numbers of birds available to hunters (Tapper 1999). The birds are placed into open topped pens in woodlands at 6-8 weeks of age where they are allowed to acclimatise to their new environment before dispersing into surrounding countryside over the following weeks. Pheasants are released at an average stocking density of 1800 birds per ha of release pen (Sage et al. 2005). Consequently, due to the high density of birds in and around release pens, pheasants are vulnerable to infection with helminth parasites. Intensively managed wild pheasant populations which can reach densities of around 150/km² in the autumn are also susceptible to parasitic infection (Draycott et al. 2002). Recent studies have shown that helminth parasites can have negative effects on survival in juvenile pheasants (Millán et al. 2002), and on survival of adult hens during incubation (Woodburn, 1999).
Over winter mortality of released pheasants in Britain is approximately 80% (Turner & Sage, 2004) but due to the large numbers released, significant number of birds are alive at the beginning of the breeding season (50-100 birds/km²). However, the breeding success of these birds is often poor (Hill & Robertson1988; Hoodless et al. 1999). Many factors have been implicated as contributing to this poor breeding success including susceptibility to high levels of endo-parasitic infection (Draycott et al. 2002). Woodburn (1999) found direct dosing released pheasants with an anthelmintic increased their breeding success to comparable levels of wild pheasants. Direct and indirect anthelmintic treatments have been shown to reduce parasite burdens and improve breeding success in red grouse (Hudson et al. 1992, Newborn & Foster 2002). Woodburn et al. (2002) showed that indirect anthelmintic treatment in spring significantly reduced burdens of Heterkis gallinarum and Capillaria sp. which are the most prevalent parasite species of pheasants in Britain (Draycott et al. 2002). The aim of this study was to determine the effect of the anthelmintic treatment on the breeding success of pheasants.