Feeding garden birds: for better or worse?

Blue tit and great tit eating peanuts from garden feeder
Image by Kev from Pixabay

Every January, I spend a blissful hour watching birds in the garden, joining over half a million people in the UK for the RSPB’s Big Garden Birdwatch. Feeding garden birds is now a popular activity worldwide, with public interest in feeding wild birds soaring during the Covid pandemic. Indeed, scientific research shows a surge in Google searches for bird food and feeders across 115 countries in the northern and southern hemispheres during the general lockdown. In the UK alone, we spend an estimated £200-300 million on bird feeding products each year (2019), providing enough food for 196 million birds. This far exceeds the energy needs of the combined total population of many common garden species.

Like many people who feed birds, I want to help them through the winter. But even the breeding season is a challenge for birds now as agricultural intensification, climate change and urbanisation impact natural food sources, prompting us to feed birds year-round. But are we doing more harm than good?

Thinking about the pros and cons of our well-intentioned intervention, I find myself in a quandary. Should I cut back or stop altogether? On the one hand, a constant supply of food benefits individual wild birds and a range of species. Watching their antics gives me joy and respite from stress and I like to think I am helping the birds too. On the other hand, I am aware of the negative impacts of supplementary feeding such as disease transmission, poor nutrition, predator attraction, food dependency, and giving an advantage to abundant species at the expense of declining species. So, how do the benefits and drawbacks weigh up and is it time to reconsider this popular human activity?

Benefits of providing food for garden birds

1. Supplementary food offers a lifeline

In winter, harsh weather and reduced hours of daylight make it challenging for wild birds to find food and keep warm; wild food is less abundant and water sources may be frozen. In summer, water sources dry up during droughts and hardened earth prevents access to insects and worms. By putting out food, we may help birds survive the winter and even influence their fitness for breeding. Our food may also help adults feed their chicks, especially when songbirds are breeding earlier due to climate change, but prey such as caterpillars have not yet emerged or reached peak availability to meet demand. Once we start providing extra food, it can be hard to stop if we think the birds depend on it.

2. Diversity and populations increasing in gardens

Every winter since 1970, the BTO Garden Bird Feeding Survey (GBFS) has recorded bird activity in approximately 250 gardens where people feed birds; initially food provision was mealtime leftovers but now includes products supplied by a booming industry. GBFS data suggests these changes have increased the variety of birds visiting our gardens from 15.9 species during autumn and winter in 1970–71 to 22.7 species during the winter of 2010–2011. Using this data, researchers from BTO confirm that feeding birds is having a major influence on garden bird communities in Britain, increasing both the populations of certain species as well as the diversity visiting feeders.

In the 1970s, House Sparrow and Starling dominated garden bird feeders. Today, more species take advantage of the range of supplementary foods on offer with Goldfinch and Woodpigeon reported by over 80% of GBFS participants compared to fewer than 20% in 1973. The BTO study even found the number of feeders in a garden has a greater influence on species richness and diversity than winter temperature or local habitat. Researchers therefore suggest, “Greater coordination of feeding activities, across networks of gardens and at multiple spatial scales, could be an innovative way of delivering large-scale conservation or species management outcomes in the future.”

3. Human wellbeing and connection with nature

Feeding garden birds helps connect people with nature and provides opportunities for enjoyment, relaxation and learning. This wildlife experience is especially important for people who are housebound and/or lonely, and for those living in cities who cannot easily access the countryside or coast. Feeding birds is widely accessible, whether in private gardens or on balconies in apartment blocks. “As urban expansion continues both to threaten species conservation and to change peoples’ relationship with the natural world, feeding birds may provide an important tool for engaging people with nature to the benefit of both people and conservation,” researchers suggest.

Drawbacks of feeding garden birds

1. Disease transmission

If we do not clean feeders each week and empty and refill water baths and dishes daily then stale food, regurgitated or partially chewed food, and faeces can spread diseases. Food provisioning at feeding stations attracts a variety of species to one location on a regular basis and in much higher numbers than natural habitats where these species may not interact closely if at all. Using citizen science data, BTO researchers looked at the health hazards associated with feeding garden birds by exploring relationships between supplementary feeding, disease epidemiology and population dynamics, concluding that wild birds are at risk of serious diseases at garden bird feeders.

How can we reduce the risk of disease transmission? The BTO study on health hazards noted that compliance with requests to stop feeding birds for disease prevention is likely to be low. So, rather than ban feeding, which has benefits for people and birds, researchers suggest focusing on reducing or redistributing the volume or type of food provided and promoting optimal hygiene measures. Educating the public about disease transmission in garden birds, the deadly impact of outbreaks, and prompt action to limit transmission could help people accept evidence-based, best-practice advice. They suggest encouraging people to report signs of disease to the Garden Wildlife Health (GWH) initiative; to contact a veterinarian or local wildlife rescue for advice; and to take a break from feeding to prevent further transmission.

Based on this research, co-author Kate Risely offers a sensible approach to feeding garden birds. “We’re calling on everyone who feeds wild birds to be aware of their responsibilities for preventing disease. Simple steps we’d recommend include offering a variety of food from accredited sources; feeding in moderation, so that feeders are typically emptied every 1-2 days; the regular cleaning of bird feeders; and rotation of feeding sites to avoid accumulation of waste food or bird droppings.”

Greenfinch eating seeds from garden feeder
Image by JacekBen from Pixabay

The Garden Wildlife Health (GWH) website explains diseases in wild birds, such as trichomonosis, salmonellosis, avian pox, and leg lesions. Trichomonosis has decimated Greenfinch populations. Since 2006, the UK breeding population declined from around 4.3 million to around one million birds, representing a decline of 77% according to the Breeding Bird Survey (2021). Ironically, the Greenfinch population had risen dramatically in the 1990s as these birds exploited garden feeders. Trichomonosis is also thought to be driving the decline in the UK breeding population of Chaffinch with declines more marked where supplementary feeding in gardens is common. Other birds such as House Sparrow, Dunnock, Goldfinch, and Blackbird are also at risk if they visit gardens frequented by infected finches.

GWH recommends the following year-round best practice for feeding garden birds to help control and prevent disease transmission: clean and disinfect feeders and feeding sites regularly; provide fresh drinking water and rinse or clean birdbaths and dishes daily; provide fresh food from accredited sources; rotate feeders to avoid contamination in one area; and clear up food on the ground each day.

2. Unbalanced diets and poor nutrition affect fledglings

Supplementary food may compromise fledgling health and breeding productivity if the food is of poor nutritional value or provides an unbalanced diet compared to wild food. A collaborative study by the University of Exeter, the BTO and the University of Turin found reduced breeding performance in woodland Blue Tits given access to extra food the previous winter. These birds produced young that were smaller, weighed less and had lower fledging success than adults that were not fed.

Although reasons for this carryover effect are not clear, it could be that the fed birds had an unbalanced diet or that winter feeding created an “ecological trap” that encouraged birds to reproduce at a level that couldn’t be sustained. Another reason is that the extra food in winter may have allowed adults in poor condition to reproduce, thereby reducing breeding success within the population.

Similarly, a study of turtle doves in East Anglia found that young Turtle Doves raised on a diet of seeds foraged from wild arable plants rather than commercial seeds in gardens are more likely to survive after fledging. Unaware Turtle Doves were feeding in gardens as much as they seem to be, researchers are concerned these easy meals may be an “ecological trap” tricking the birds into eating foods that aren’t good for them and/or their offspring. An alternative explanation could be that adults pick up parasites at bird feeders and baths and this hinders young doves’ development. To help Turtle Doves, lead researcher Dr Jenny Dunn says: “The answer is to leave a weedy patch in your garden – what turtle doves need is natural weed seeds and areas of bare ground.”

Wild birds are not only at risk of an unbalanced diet in private gardens. Pigeons, gulls and ducks are often fed human leftovers, which have poor nutritional value for birds. A study on the nutritional implications of feeding wild birds in public urban areas found that bread was the most popular food offered (68%) in Amsterdam, followed by other remains of human food (29%). Half of respondents did not know whether the food was good for the birds. The species most attracted to this food were Feral Pigeon, various gull species, Domestic Goose, Starling and Jackdaw. Reasons given for feeding birds leftovers included not wasting it. The quantities fed to birds was mostly determined by the amount of leftover food rather than the number of birds present. Observations were made in daylight, so researchers could not confirm if a surplus of bread and leftovers at the end of the day is sustaining rodent populations. Researchers noted that Brown Rats are known to predate on the chicks and eggs of waterfowl, which could be problematic where there is an abundance of rats.

3. Disruption of species population dynamics

In their article in British Birds, Dr Richard Broughton, Dr Jack Shutt and Dr Alexander Lees discuss the impact of feeding garden birds. “We provide blue tits and great tits with easy food and millions of nest boxes. What does this mean for the other species that share their habitat with these subsidised birds?” the authors ask.

Marsh tit perched on tree branch
Image by Frauke Riether from Pixabay

While species benefit from supplementary feeding, especially in terms of winter survival, other less dominant species may be losing out. This is evident in the decline in woodland birds like Marsh Tit and Willow Tit that compete for nesting sites and natural food sources with species that capitalise on feeders such as Blue Tit and Great Tit and even Great Spotted Woodpecker. “British Willow Tits have far higher nest losses than other tits, or Willow Tits elsewhere, and the main cause of that is eviction by Blue Tits and predation by Great Spotted Woodpecker,” says Broughton based on his research. And the increase in Blue Tit and Great Tit populations is not the only problem; the food-caching behaviour of Marsh and Willow Tits may involve constant visits to feeders, making them an easy target for Sparrowhawks. Willow Tits would rarely be caught by Sparrowhawks otherwise, says Broughton. He advocates not feeding in areas where Marsh and Willow Tit populations are at risk of local extinction.

A study led by Shutt shows the high proportion of supplementary food in the diet of wild birds such as Blue Tit, peanuts in particular, and reports the distances they travel to feeders are greater than imagined. Populations of woodland bird species using supplementary food resources are increasing while species that do not use these resources and/or are outcompeted by Blue Tits are declining. This change in population and ecosystem dynamics caused by supplementary food has implications for biodiversity conservation, so the researchers urge policymakers to be cautious about advocating supplementary feeding for wildlife engagement. They also suggest the removal of feeding from nature reserves, a reduction in the encouragement of feeding in areas known to be important for threatened species, and a reversion to winter-only feeding rather than year-round, with each suggestion recommended as potential research areas.

Lees acknowledges that House Sparrows and Starlings in cities may depend on human handouts. Likewise, Tree Sparrows in barren countryside. But he advocates an informed and responsible approach to feeding garden birds so that dominant generalists don’t put more pressure on struggling specialists. “We urgently need an evidence-based approach to bird feeding, the current approach is driving disease epidemics and trophic cascades which are causing avian biodiversity loss,” says Lees.

4. Feeding stations provide a larder for predators

By attracting birds to our garden feeding stations, we expose them to predation by providing a reliable and easy food source for birds of prey, crows, and cats. There may also an increased risk of nest predation near garden feeders. Cats are constant prowlers around feeders, and in my garden, I have also seen Sparrowhawks take Blackbirds. At least their predation is for survival, but it isn’t my ideal garden birdwatching experience.

5. Commercially produced seed may not be sustainable

Feeding birds with commercially supplied seeds can be expensive if you feed daily and want sustainably grown seeds. However, cheaper seeds may well come at a cost to nature and biodiversity if land is cleared of natural habitat and pesticides used. It seems counter-intuitive to grow monocrops on a vast scale to feed birds when we could provide wild food for birds through nature-friendly farming and wildlife gardening, and restrict commercial seeds to the winter months. Growing native fruit trees, berry-bearing shrubs, and seed-bearing, nectar-rich flowers, which support insects, and avoiding the use of chemicals is a healthy and sustainable way to provide food for wild birds.

Greenfinch perched on a sunflower
Image by Frauke Riether from Pixabay

Feeding garden birds has benefits for people, birds and commercial food producers and suppliers. However, there needs to be greater public and industry awareness of disease transmission, predation risk, and biodiversity impact, so we can feed birds responsibly. Further research could inform best practice on where, what and when to feed wild birds, so that all species have the chance to thrive. The final word goes to Dr Alexander Lees, who sums up how best to help wild birds: “Where possible, improving habitat amount and quality in our gardens is a vastly more important gift to nature than any bird seed handouts.” 

This article was first published in the January 2024 issue of the North East Norfolk Bird Club newsletter.