A selective review of evidence with a focus on two unpublished PhD theses
Releasing pheasants (Phasianus colchicus) and red legged partridges (Alectoris rufa) for shooting is widespread across lowland UK, yet the ecological effects of this practice on ground dwelling invertebrates remain only partially understood. This selective review summarises published evidence relating to possible effects of released pheasants and red-legged partridges on ground invertebrates inside and alongside release pens.
The focus of this review is two PhD theses (Callegari, 2006 and Pressland, 2009) that have previously received limited peer-review relating to the possible effects of these gamebirds on soil-surface or ground invertebrates in woodland and unimproved grassland areas adjacent to release sites. Existing research indicates that high densities of pheasant poults within woodland pens can significantly reduce certain larger invertebrate groups, particularly carabid beetles, likely through a combination of direct predation and habitat alteration via soil disturbance, trampling, and nutrient enrichment. Away from release pens, dietary studies show that free living adult pheasants consume relatively low proportions of invertebrates (typically <5%), though seasonal peaks of 5–20% have been recorded at woodland edges. Evidence from species rich grasslands suggests that dispersed gamebird populations, even at moderate densities, do not measurably reduce local invertebrate abundance.
Overall, the data suggest that impacts on ground invertebrates are largely localised to areas where released birds accumulate at high densities, such as pens, feed stations, and woodland edges, whereas effects decline rapidly with increasing distance and bird dispersal. The review identifies key knowledge gaps, including the need for studies on specialist invertebrates and on the spatial extent of release related pressures on invertebrate communities. The results provide the basis for some specific management recommendations relating to reducing high density accumulations of birds around release points, feeding stations and other hotspots at sensitive sites.