Impact of game bird release on the Adonis blue butterfly Polyommatus bellargus (Lepidoptera Lycaenidae) on chalk grassland

Abstract

Polyommatus bellargus is a priority species of butterfly in the UK as a result of its scarcity and the rate of population decline over the last few years. In the UK, the species is associated with chalk grassland on hot, south-facing slopes suitable for the growth of the food plant Hippocrepis comosa. Shooting game birds is a popular pastime in the UK. Over 40 million game birds, principally Phasianus colchicus and Alectoris rufa, are bred and released into the countryside each year for shooting interests. There is a concern that the release of such a large number of non-native birds has an adverse effect on native wildlife. A study was carried out over a period of 3 years out to examine whether there was any evidence that A. rufa released into chalk grassland habitat negatively affects populations of P. bellargus. A comparison was made between sites where large numbers of A. rufa were released versus sites where no, or few, birds were released. The study involved the construction of exclosures in these sites to allow an examination of the number of butterflies emerging from H. comosa when the birds were excluded versus when the birds had free range across the area. Where birds were present the on-site vegetation was shorter than where they were absent indicating that the birds were definitely influencing habitat structure. However, the evidence that A. rufa was negatively influencing the number of adult butterflies emerging was not strong, although there was a largely non-significant tendency for higher butterfly emergence when the birds were excluded or absent.

Why do many pheasants released in the UK die, and how can we best reduce their natural mortality?

“…Although release of game birds and their subsequent shooting can stimulate significant environmental management that benefits a wider range of species and habitats (Mustin et al 2018), release of game birds, especially at high numbers/ densities, can also contribute to environmental damage. This includes adverse modification of woodland ground flora and fauna within their immediate release pens (Neumann et al 2015;Sage et al 2005) and impacts on the broader environment (Callegari et al 2014;Sage et al 2009). Finally, the waste of so many birds also raises ethical questions, especially when eggs are produced and young birds reared in unnatural commercial conditions before being released to face natural perils such as starvation or predation (Matheson et al 2015).…”

Summary review and synthesis: effects on habitats and wildlife of the release and management of pheasants and red‐legged partridges on UK lowland shoots

“…Partridges can however be released into or alongside more sensitive grassland habitats. Callegari (2006) [ntl] found that although the gamebirds were eating some invertebrates on several chalk grassland sites (based on faecal sample analysis), mainly following release in autumn, they did not have a measurable impact on overall spring invertebrate densities, or on numbers of Adonis blue Polyommatus bellargus butterfly, which were studied in particular detail Callegari et al (2014) [ntl].…”

The effects of released pheasants on invertebrate populations in and around woodland release sites

“…Our study involving 49 release pens over 2 years releasing at relatively high densities detected some evidence to support this hypothesis, but also indications that this is not a ubiquitous process, with those effects that we did detect often restricted to particular taxonomic groups and that the size of the effects was small compared to variation across different years when climatic or environmental effects may influence invertebrate population's size or activity. We did not explicitly look at effects on particular species, but this would be informative, especially if releases occur in areas where species of conservation concern are found (Callegari et al., 2014 ). The differential effects on particular invertebrate taxa that we detected could be due to direct predation, with pheasant targeting preferred, more available, or more conspicuous prey.…”