Examining the spatial relationship between pheasant (Phasianus colchicus) release pens and grey partridge (Perdix perdix) population parameters.

Abstract

Throughout the 20th century, numbers of grey partridges (Perdix perdix) in Britain (and in other countries) have declined (Potts and Aebischer, 1995). These declines have been related to increases in the intensification of farming systems, leading to lower numbers of chick-food insects and decreased chick survival, a decline in field boundary nesting cover, and an increase in predation pressure during nesting (Potts, 1980 and 1986; Rands, 1986; Aebischer, 1997; Tapper, 1999). These declines have lead to changes in the relative importance of different quarry species in the UK. The grey partridge, from being the most commonly shot species, has declined in importance, while increasing releases of pheasants (Phasianus colchicus) and red-legged partridges (Alectoris rufa) have led to their prominence in modern-day lowland gamebags (Tapper, 1992 and 1999).
This switch, from shooting wild grey partridges to shooting released birds, specifically pheasants, has led to concern about adverse effects on grey partridges. Some that have received attention in the past are:
Aggressive interactions between pheasants and grey partridges, with grey partridges coming off worse (Jenkins, 1961).
Pheasants laying eggs in the nests of grey partridges, resulting in decreased hatching success of grey partridge chicks (Jenkins, 1961)
Changes in the style of gamkeepering from augmenting the natural abundance of wild birds to maximising the production and presentation of reared birds (Tapper, 1992)
Changes in habitat management within an estate, with management either decreasing when relying on released birds or a changed emphasis to providing woodland edge to benefit pheasants (Tapper, 1992)
Recently, the release of pheasants in the environment has come under additional scrutiny as those released birds may serve as reservoirs of parasitic infections (especially the caecal nematode, Heterakis gallinarum), that have been postulated to have a detrimental effect on numbers of wild grey partrides (Tompkins et al., 2000). It has been suggested that the transmission of H. gallinarum from pheasants to grey partridges may have contributed to the declines witnessed over the past century. If this were the case, one would predict that areas close to release pens would show a greater decline in density of grey partridges and those partridges found closer to release pens would have lowered survival and fecundity. This paper seeks evidence for such adverse effects of pheasant releasing in two long-running datasets combining annual counts of grey partridges and locations of pheasant release pens.