A Belgian study has demonstrated a link between the mass release of Common Pheasants and the disappearance of lizards and snakes from the environment.
The research, carried out in Wallonia, also found that stopping the release of pheasants in an area led to recolonisation by a widespread species of lizard within a few years.
Published in the Bulletin de la Société Herpétologique de France, the researchers presented several key findings. First, they made extensive field studies at six sites at which pheasants were mass released. Regardless of how many visits they made, no reptiles were found at any of the sites. By comparison, an average of more than three species of squamates (minimum one species, maximum six) were recorded at sites not subjected to gamebird releases in the same area.
Secondly, at a site where pheasants were released in 1999, no Common Lizards Zootoca vivipara could be found within a 2.5-km area (measured in five sections of 500 m from the release site). In 2011, a few years after the pheasant releases had stopped and the birds had died out, Common Lizards were detected in four of the five sections. To ensure that this wasn't a coincidence related to a comeback of Common Lizard in the wider area, the researchers compared results to the control areas, free of pheasants. They found that the population had remained stable, suggesting that the presence of pheasants was key to the abundance of lizards.
Researchers found that Common Pheasant is responsible for severe declines – and even some local extinctions – in various snake and lizard species in Belgium (Jane Rowe).
Additionally, the scientists pointed to the absence of Slow-worm Anguis fragilis from sites subject to mass pheasant releases as particularly significant. It is, they say, the commonest squamate in Wallonia and can be present in densities of up to several hundred individuals per hectare and is easily detected using artificial shelters. For none to be detected in pheasant-release areas, the impact of the gamebirds on the reptiles must be huge. As with Common Lizard, Slow-worms were observed to return to areas once pheasants disappeared.
While it may be possible for abundant species to recolonise, the authors point out that the same does not apply for rare or localised species. For example, a decade after the cessation of pheasant releases at a site formely occupied by Adder Vipera berus in the Belgian province of Namur found no evidence of recolonisation, with pheasants having probably led to the localised extinction of this isolated population.
In arable farming areas, where the reptiles are confined to small patches of suitable habitat and form isolated populations, the risk of permanent local extincitons following over-predation by pheasants, even temporary, is high.
Given the evidence presented, as well as previous studies that have shown that mass releases of pheasants cause significant impacts on the flora, vegetation and arthropod communities, the authors say that banning pheasant releases would be the recommended course of action, as has already happened in other European countries such as The Netherlands.
Graitson, E, & Taymans, J. 2022. Impacts des lâchers massifs de faisans de Colchide (Phasianus colchicus L) sur les squamates (Reptilia Squamata). Bulletin de la Société Herpétologique de France. DOI: 10.48716/bullshf.180-2.