Comparative Population Dynamics of Wild and Reared Pheasants (Phasianus colchicus).

Abstract

The release of reared pheasants (Phasianus colchicus) occurs annually in Britain, but research has shown that survival and breeding success of reared birds is poor compared to their wild counterparts. The main aim of this study was to assess the impact that rearing may be having on pheasant population dynamics.
A long-term monitoring programme of a pheasant population on one area established a relationship between rearing and the productivity of the population. As the level of rearing increased the proportion of juvenile reared females in the breeding population increased, resulting in lower chick production. Although comparative studies between wild and reared, and between adult and juvenile pheasants highlighted differences, they were insufficient to account for the negative effect of rearing.
One possible hypothesis to explain this was the effect of parasitism. Infection with the caecal nematode, Heterakis gallinarum, in pheasants was positively related to the level of rearing. These are common parasites of pheasants and are easily transmitted between hosts. Experimental treatment of reared female pheasants with an anthelminthic resulted in improved survival during incubation and increased chick production to a level similar to that of wild females.
Further investigation of parasitic nematode infection revealed a rapid seasonal increase in their availability to pheasants, the likelihood of arrested development of immature larvae, and the possibility of an existing worm burden inhibiting subsequent infection.