How shared bird feeders might be fueling a lethal parasite spread

Nature · Published 19 October 2026 Swipe more like this →

In short: While supplementary feeding helps birds survive, it can also create a hotspot for disease. Research suggests that high-density feeding resources may act as transmission hubs for parasites, potentially turning a well-intentioned act of conservation into a significant risk for wild bird populations.

While Trichomonas gallinae commonly infects columbids, it has recently become a deadly ailment for passerines, especially finches. Recent screening of 363 birds across the UK and France revealed that the parasite is present in 79% of columbids and 36% of non-columbids. Crucially, the study found that the Type A strain of the parasite is transmitted via shared resources, such as food and water, rather than just direct bird-to-bird contact. The study screened 261 columbids and 102 non-columbids to identify these strains. Researchers also analyzed 51 specific food and water resources common in farmland. They conducted this screening across 12 different sites over a two-year period.

The mechanism of spread is tied to density. Researchers screened 51 environmental resources over a two-year period and found that T. gallinae was isolated from high-density feeding resources nearly three times as often as low-density natural areas. Additionally, birds collected from fed locations showed over twice the Type A strain frequency than those from unfed areas. This suggests that concentrated feeding stations can facilitate the 'spillover' of parasites from reservoir hosts to more vulnerable species. The study isolated the parasite from 39% of environmental resources. Birds collected from locations with food showed Type A strain rates exceeding twice those found at sites without feed. These findings provide compelling evidence for transmission via shared resources.

For conservation groups like the RSPB, which manages over 200 nature reserves and engages 1.2 million members in nature connection, these findings highlight a critical nuance in wildlife management. While the RSPB works to restore habitat and diversity, the science suggests that the way we provide supplementary food matters. Research suggests that providing supplementary food at low densities could be a vital method for shielding wild bird groups from fatal infections by limiting parasite spread. The RSPB has been advocating for nature protection for 135 years. They manage more than 200 nature reserves across the UK. They have helped create South Atlantic marine sanctuaries measuring triple the UK's total area.

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