Food and water stations for wild birds contributing to deadly disease spread

Food and water stations for wild birds are contributing to spread of deadly disease, Leeds-led research has shown, with birds three times more likely to catch a parasite from these resources.

Led by Dr Rebecca Thomas, as part of her PhD work in the School of Biology and co-supervised by Dr Simon Goodman in Leeds and Dr Jenny Dunn from Keele's School of Life Sciences, the new research published in the journal Molecular Ecology looked at the prevalence of the parasite Trichomonas gallinae in farmland birds.

Trichomonas gallinae is widespread worldwide in birds from the pigeon and dove group, known as columbids, where it is a conservation threat to some endangered species such the turtle dove (Streptopelia turtur).

The parasite also causes a lethal disease in another class of birds known as passerines, which are common in gardens and include well-known songbirds like finches, warblers, and sparrows.

Dr Simon Goodman

Previous work has suggested that the parasite may be transmitted between birds through shared food and water in gardens, but more information is needed on how the parasite is transmitted between species and to what extent it persists in the environment.

Dr Goodman said: “Supplementary feeding of wild birds on farmland has been seen as an important conservation measure in response to declining food resources and intensive agriculture, which impact endangered species such as turtle doves. This work shows we need to change aspects of supplementary feeding practices, to keep the benefits while managing the disease transmission risks.”

One hypothesis has suggested that this parasite might be transmitted at shared food and water resources which are commonly used on farmland to help wild bird populations. Providing supplementary food on farms is widespread as a conservation measure to support endangered wildlife species including turtle doves, and to sustain gamebirds such as pheasants.

Screening shared food sources

To test this idea, the research team used DNA sequencing to screen 363 birds in the UK and France, as well as 51 shared food and water resources, at 12 farmland sites over a two-year period. The DNA tests confirmed the presence or absence of the parasite, and identified which strains were present.

The birds sampled were both columbids and non-columbids, and included birds who fed at high density shared food resources where supplementary feed stations were set out, as well as from low density, natural sources like seed-providing vegetation.

Their results showed that T. gallinae parasites were present in 79% of the columbid birds screened, 36% of the non-columbids, and 39% of the shared environmental resources.

One strain of the parasite, known as Type A, was more than doubly prevalent in the birds who fed at high density resources compared to lower density, more natural sites, and it was also found nearly three times as often at the high-density feeding sites themselves compared to the natural feed sites. The Type A strain is a more virulent strain that has been linked to mortalities and population declines in UK greenfinch populations.

Improving conservation policy and practice

Dr Thomas said: “This study is an important example of how novel techniques like DNA-based disease monitoring can give new insights into how parasites impact wildlife populations, and help us develop more informed conservation policy.”

These findings provide strong evidence that the parasite is transmitted to different birds from these shared resources, with the researchers saying that carefully managing supplementary feeding resources on farms and making them as low density as possible could help reduce parasite transmission.

This study is an important example of how novel techniques like DNA-based disease monitoring can give new insights into how parasites impact wildlife populations, and help us develop more informed conservation policy.

Dr Rebecca Thomas

This will help to protect the health of the birds that feed there, while still providing necessary resources to help breeding farmland birds. The same applies in gardens, with new guidance by the Royal Society for Protection of Birds (RSPB) asking people to feed birds seasonally and safely.

An example of carefully managed, low density supplementary seed provision has been successfully trialled for Turtle Doves, and now forms part of the Operation Turtle Dove management package for the species.

Dr Dunn added: "Our findings demonstrate that the Trichomonas gallinae parasite is much more widespread that we were expecting, and suggest that food and water are key to parasite transmission. However, this knowledge also gives us the tools to manage environmental resources such as supplementary food, to reduce parasite transmission between birds and hopefully reduce mortality."

Dr Thomas's PhD work was supported by a PhD scholarship from the Royal Society for Protection of Birds (RSPB) and Natural England, under the Action for Birds in England partnership, and by a grant from the Natural Environment Research Council (NERC) for use of the National Biomolecular Analysis Facility at the University of Sheffield.