The long-term impacts of finch trichomonosis have prompted a review of the scientific evidence surrounding garden bird feeding. This review was led by RSPB, with significant input from BTO and colleagues at the Institute of Zoology. The review examined the possible pros and cons of feeding wild birds, using published science to establish what we know and what we don’t. It looked at how the provision of food influences individuals, populations and communities, through effects on survival, disease risk and competition, amongst other factors.

Both RSPB and BTO have used the review to update the advice we give on feeding wild birds.

Addressing finch trichomonosis

The strongest scientific evidence in the review relates to disease transmission at feeding stations – notably of finch trichomonosis. BTO research has played a central role in our understanding of finch trichomonosis and its effects. Our work links the disease to residential settings and garden feeding stations. Ongoing collaborative research between the RSPB, the Institute of Zoology and BTO is further examining how feeding practices influence disease dynamics. Recent results from this work identify the post-breeding period as a time of elevated outbreak risk in gardens. These findings have directly informed the view that best practice advice on when to feed should now include a seasonal component.

A complementary field-based study is investigating transmission routes at shared food and water resources in gardens. Early results from this work have helped to clarify how feeder design and hygiene measures influence disease risk, informing practical decisions, such as the halt to sales of ‘flat surface’ feeders announced by RSPB and BTO partners Vine House Farm back in the winter of 2024/25. These flat surface feeders appear to carry a higher risk of onward transmission than is the case with hanging feeders.

Taken together, this growing body of evidence points most clearly to disease transmission at feeding stations as the area where mitigation is both feasible and likely to be effective.

What are the main recommendations?

We advise feeding in ways that:

• reduce repeated use of the same feeding spots by large numbers of birds,
• avoid creating predictable, long-lasting feeding sites where contamination can build up,
• encourage movement and turnover, more like natural food patches that appear and disappear,
• adjust food types seasonally, particularly during higher-risk periods,
• retain the benefits of feeding while reducing unintended disease risk.

What does feeding seasonally mean?

Seeds and peanuts are foods favoured by finches, including those species whose populations have been impacted by finch trichomonosis. The scientific evidence indicates that the risks from finch trichomonosis are increased during the post-breeding period, so limiting access to these foods at this time of the year provides our best chance of lowering transmission risk. The advice is to feed seeds and peanuts from November to April, but to pause their provision during May to October.

The updated guidance also highlights the importance of water hygiene, since water sources can be a transmission route for the Trichomonas parasite. If you, or a neighbour, has a shallow-edged pond that allows birds to drink and bathe, there is generally no need to provide additional water unless the pond has dried out or frozen. Where water is provided, replace it daily. Bowls or trays should be cleaned weekly, then rinsed and dried before reuse.

Whatever the time of year, good hygiene remains essential – offer food little and often, clean feeders regularly, and move them periodically to reduce build-up of waste and contamination.

Are flat-surface feeders safe to use?

As noted, flat surface feeders appear to carry a higher risk of onward transmission than is the case with hanging feeders, so are best avoided.