Mass releases of pheasants linked to severe declines in reptile populations

A Belgian study demonstrated a link between the massive release of common pheasants and the disappearance of lizards and snakes from the environment.

The research, conducted in Wallonia, also found that stopping the release of pheasants in an area led to recolonization by a widespread lizard species within a few years.

Posted in the Bulletin of the Herpetological Society of France, the researchers presented several key findings. First, they carried out extensive field surveys at six sites where pheasants were released en masse. 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 subject to game bird releases in the same area.

Second, 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 500 m sections from the release site). In 2011, a few years after the cessation of pheasant releases and the disappearance of the birds, common lizards were detected in four of the five sections. To ensure that it was not a coincidence linked to a return of the common lizard to the enlarged area, the researchers compared the results to control areas, free of pheasants. They found that the population had remained stable, suggesting that the presence of pheasants was the key to the abundance of lizards.


Researchers have found that the common pheasant is responsible for severe declines – and even some local extinctions – of various species of snakes and lizards in Belgium (Jane Rowe).

In addition, scientists have pointed out the absence of slow worms Anguis fragilis from sites subjected to mass releases of pheasants as particularly important. It is said to be the most common squamate in Wallonia and can be present at 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 game birds on reptiles must be enormous. As with the common lizard, slow worms have been observed to return to areas once the pheasants have disappeared.

While it is possible for abundant species to recolonize, the authors emphasize that the same is not true for rare or localized species. For example, a decade after the cessation of pheasant releases at a site formerly occupied by Adder berus viper in the Belgian province of Namur found no evidence of recolonization, as pheasants probably led to the localized extinction of this isolated population.

In areas of agricultural cultivation, where reptiles are confined to small patches of suitable habitat and form isolated populations, the risk of permanent local extinction following even temporary overpredation by pheasants is high.

Considering the evidence presented, as well as previous studies that have shown that mass releases of pheasants have significant impacts on flora, vegetation and arthropod communities, the authors argue that a ban on pheasant releases would be the recommended course of action, as has already happened in other European countries such as the Netherlands.

Reference

Graitson, E, & Taymans, J. 2022. Impacts of mass releases of ring-necked pheasants (Phasianus colchicum L) on squamates (Reptilia Squamata). Bulletin of the Herpetological Society of France. DOI: 10.48716/bullshf.180-2.

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