The role of pheasant releases in ecosystems is complicated and evidence does not support some of the assumptions made about gamekeeping, according to a paper presented to an online ornithologists conference.

The paper used data from the poultry register to work out where pheasant releases were taking place and matched it against citizen science data from the NBN Trust. The scientists also identified control areas where no releases were taking place. While the effect on biodiversity of releasing pheasants was unclear, release sites were generally more biodiverse than sites where pheasants were not released, but the researchers pointed out that this may be due to more time and effort being put into studying those sites.

However, they were very clear that if the same amount of study had gone into both sites then areas where birds are released are significantly more biodiverse than areas where they are not.

Impacts of pheasant releases

The study builds on and strengthens work conducted by Pheasants at Exeter and the GWCT which looked at the impacts of pheasant releases in light of the claims made by Wild Justice that pheasants were harming protected sites. That study found little negative impact on biodiversity away from the release pens themselves. In recent years an idea called the Overspill-Predation Hypothesis has been promoted by several groups and individuals. Its proponents claim that having large numbers of birds released into the countryside gives a boost to predators such as foxes and crows which then go on to predate other wildlife.

The paper looked at how close a match there is between pheasant releases and predator numbers. Comparing areas where pheasants are and aren’t released showed that fox numbers are lower where pheasants are released and that releasing more pheasants is connected to having fewer foxes. It also noted a weak connection between the numbers of pheasants released and increased numbers of carrion crows and jays.

There was no clear connection between pheasant and buzzard numbers, but pheasant releases led to a clear increase in numbers of rats and grey squirrels.