22-04-2025
We're Releasing Millions Of Birds. The Ticks Are Thriving.
BURSA, TURKIYE - OCTOBER 07: A pheasant is seen among grasses in Bursa, Turkiye on October 07, 2024. ... More Pheasants are not native to the UK, but millions are released every year for shooting. (Photo by Alper Tuydes/Anadolu via Getty Images)
Each summer in the UK, up to 50 million pheasants are released into woods and fields for recreational shooting. At their seasonal peak, the biomass of these birds rivals that of all native UK breeding birds combined — an astonishing ecological intervention repeated year after year. The practice is legal, well-established, and supports rural economies. But new evidence suggests it may also be increasing the prevalence of Borrelia — the bacterial cause of Lyme disease — in local tick populations.
The study, published in Ecology Letters, found that ticks from pheasant-release sites were more than twice as likely to carry Borrelia bacteria as those from comparable control woods where pheasants had not been released. The increase was especially pronounced for Borrelia garinii, a bird-adapted genospecies linked to neurological Lyme disease in humans. This result fits into a broader pattern of rising Lyme disease incidence in the UK and across the northern hemisphere.
Lyme disease increased in the UK from 2013 to 2021.
It's long been known that pheasants can serve as competent reservoirs for Borrelia. A 1998 study showed they could remain infectious for months without obvious symptoms. But until now, it wasn't clear whether that trait translated into real-world effects. The new study moves us one step closer to answering that question.
What it does not show — and this distinction is crucial — is whether people are getting sick as a result. The increase in Borrelia prevalence in ticks is biologically meaningful, but its implications for human health remain unproven. Whether Borrelia amplification by pheasants poses a risk to gamekeepers and land managers, or even to the general public through broader ecological diffusion, is still unknown.
Even so, the results deserve attention. Wildlife management often aims to maintain populations at levels that support hunting, conservation, or commercial activity. But any large-scale intervention — especially one involving tens of millions of non-native birds — will have knock-on effects. Changing disease ecologies is one of them.
Borrelia - pathogenic bacteria (Spirochaetota) responsible for Lyme disease, (Borrelia burgdorferi, ... More Borrelia spielmanii, Borrelia garinii and Borrelia afzelii give other variants of Lyme disease). (Photo by: CAVALLINI JAMES/BSIP/Universal Images Group via Getty Images)
This study adds to a growing literature showing that when we manipulate animal populations, we also manipulate the conditions under which pathogens circulate. Most released pheasants don't survive the winter. Fewer than 10% are still alive by spring. But their temporary presence may shift local tick dynamics in lasting ways — especially if they feed adult ticks, amplify infection rates, or alter the composition of host communities in subtle, under-appreciated ways.
We are still early in understanding how pheasant releases influence tick populations, infection dynamics, and host communities — and whether those ecological changes ultimately translate into measurable impacts on human disease burden. But the findings are a signal that wildlife policies should be evaluated not only for their economic or ecological aims, but also for their downstream effects on human health. To manage landscapes wisely means taking pathogens into account.
