Ask an RSPB Expert special: All about bird feeding

In April, we told you about some urgent but simple changes to our bird feeding advice to help reduce disease. Many of you got in touch to tell us about the changes you’ve made, and we’re incredibly grateful that so many people are taking action to help garden birds. Thank you! 

In this Ask an Expert special, Charlotte Ambrose looks at why these changes are so important and answers your questions on bird feeding.

To help reduce the risk of disease and protect garden birds, we have updated our advice on feeding garden birds. The message is simple: Feed Seasonally. Feed Safely.

We also recommend that you feed in moderation to avoid a build-up of old food. This will vary from garden to garden depending on how many birds visit. For this reason, we suggest feeding based on demand, which means putting out an amount that will be eaten within the times suggested below.

As a guide, food should not be left uneaten beyond the following number of days:

• Seeds and peanuts should all be eaten within one to two days and only offered from 31 October - 1 May.  
• Mealworms should all be eaten or cleared away by dusk the same day, especially if scattered on the ground. This will help to prevent any leftover mealworms being consumed by Hedgehogs (Hedgehog rehabilitators have raised this as a concern).
• Suet products can be left out for up to seven days. 

An evidence review into the pros and cons of feeding garden birds found strong evidence that feeding can promote the spread of diseases, including the trichomonosis parasite.       

 Across the UK, trichomonosis has caused serious declines in Greenfinch and Chaffinch populations and may now be causing a rapid decline among Bullfinches. The scientific evidence shows that the risk of trichomonosis outbreaks is highest in summer and autumn.

Our Conservation Scientists have worked with other experts to look at how we can best help garden birds. That’s why we are asking you to follow our advice to Feed Seasonally and Feed Safely.  

Trichomonosis is a horrible disease that makes it difficult for birds to eat and drink. Infected birds often become lethargic, lose weight and may have wet or matted feathers around their bill. The disease spreads when healthy birds consume food contaminated with the saliva of infected birds. Sadly, many birds that develop severe trichomonosis do not survive, which is why preventing its spread is so important for protecting our garden birds. 

Our advice is that it’s safe to scatter mealworms on the ground. Many ground feeding birds love mealworms, including Blackbirds and Robins. We recommend putting out only a small amount that is eaten or cleared away by dusk the same day. This will help to prevent any leftover mealworms being consumed by Hedgehogs. 

We don’t recommend scattering other foods on the ground, as these don’t tend to be eaten as quickly and could increase the chances of attracting rodents. 

There are plenty of other things we can do to support garden birds to find their own food. You could consider growing bird-friendly plants – such as Crab Apple, Holly and Ivy – which help to provide natural, safer food sources and encourage insects. A simple leaf-litter pile can also be a bird buffet, providing a rich supply of insects, spiders and woodlice for species such as Robins, Wrens and Blackbirds to forage for naturally. 

The evidence shows that the way we have been feeding garden birds seeds and peanuts is increasing the spread of trichomonosis. Currently we have no effective mitigation to reduce that risk. If we continue to feed birds in this way, it is likely that trichomonosis will continue to spread among our garden birds and cause further population declines. 

Although finches appear particularly at risk of suffering from this horrible disease, trichomonosis has also been seen in many different bird species. These include House Sparrows, Woodpigeons, Feral Pigeons, Collared Doves and endangered Turtle Doves. Although not commonly affected, Blackbirds and Dunnocks are also susceptible. Furthermore, trichomonosis can also affect birds of prey as they may feed on infected birds. 

For these reasons, we recommend that everyone who feeds birds in their gardens follows our best practice guidance, irrespective of the species they are seeing in their gardens. 

We consider these foods (mealworms and suet) low risk as a source of trichomonosis transmission.  

Finches, particularly those species experiencing serious declines because of trichomonosis, prefer to eat seeds, and if seeds aren’t available, they may divert to peanuts. That’s why we recommend not feeding seeds and peanuts between 1 May and 31 October. Finches rarely consume fat and suet (unless there are seeds visibly embedded in it). 

The availability of natural food for birds peaks during summer and autumn, and most birds collect food from quite large areas even when they are nesting. The abundance or range of most natural food plants during the period of 1 May to 31 October has increased or remained stable over recent decades. We therefore anticipate that birds will be able to adapt to us not feeding seeds and peanuts in gardens. 

We will be monitoring the response of garden birds to these changes and will review our guidance in future if necessary. 

Research shows that offering animal protein such as mealworms boosts chick survival, so we are continuing to recommend that small amounts are offered year-round. Food is also critical in winter – particularly for birds for whom it is their first winter. 

As trichomonosis mainly affects seed-eating finches and is more common in summer and autumn, we advise not offering seeds and peanuts during this period. Instead birds can be supported with protein foods such as mealworms and bird-friendly planting.

Our advice is that you pause feeding seeds and peanuts between 1 May and 31 October even if you clean your feeders every day.

Cleaning feeders and replacing unused food is an important way to reduce the risks of disease transmission and we strongly recommend people clean their feeders and replace any unused food at least once each week.  

Research into finch trichomonosis has shown that the parasite spreads via the salvia of sick birds that is left on dropped food and regurgitated water. Feeder cleaning on its own is unlikely to prevent healthy birds picking up infected food items.  

As we currently have no effective means of preventing healthy birds accessing contaminated food, our advice is to stop feeding seeds and peanuts during the high-risk period between 1 May and 31 October.  

We are conducting field trials on new feeder designs that we hope will reduce the risks of disease transmission at feeders, but the conclusions of that work will not be available until next year. 

Our evidence review found that bird tables and other flat feeders pose the greatest risk of disease transmission. 

Birds that are sick with trichomonosis often perch on flat surfaces where they attempt to feed. The disease makes swallowing food difficult, so they often regurgitate contaminated food back on to the flat surface where it is then available for healthy birds to pick up. Even daily feeder cleaning will not prevent healthy birds from eating previously regurgitated food.  

That’s why we advise that no flat-surface feeders, including bird tables and window feeders, are used to feed birds. Instead choose feeders that are easy to take apart and clean, prevent rain getting in, and limit condensation. Make sure all feeders drain easily and do not allow old food to build-up.

The best thing you can do for the birds in your garden is to create a good habitat for them with a variety of features and natural food sources that provides sustenance during all seasons. If you have the space, why not create a pond! A pond is a great way to attract a variety of wildlife, and the best way to provide birds and other wildlife with water.

You can find our advice on plants that provide food and attract invertebrates for birds on our website. These can be adapted based on the space you have available in your garden.