Each summer in the U.K., 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 U.K. 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 U.K. and across the Northern Hemisphere.