Myth: It is always helpful to feed garden birds!
 
This is not so much a myth, as a bit of an exaggeration, and one that can have seriously bad effects if not done carefully.
 
Bird feeding is the most popular wildlife gardening activity in Britain, other than growing plants.  In a recent survey conducted by YouGov for the Wildlife Gardening Forum 41% of a randomly chosen set of householders said they acted to help wildlife a lot or a fair amount.  76% of them provided supplementary food for birds.  The wild bird food industry in Britain is huge, estimated at between £200m and £300m annually. It’s clear that feeding birds isn’t entirely altruistic, people enjoy watching them through the window without the need for heavy coats and binoculars. There is evidence that feeding birds has benefit for human wellbeing by bringing people closer to nature1..
 
 
 
 
 
 
 
 
How feeding helps birds is reasonably clear. Published data show that in most cases supplementary feeding does increase adult bird condition and survival4., especially for females, in winter and during the breeding season. The effect on their reproductive success was much less clear, with as many studies suggesting it had no benefit as studies that found it improved fledging and survival. On balance it is considered likely to be beneficial5..
 
The popularity of bird feeding has created largely beneficial changes in our bird populations, although the long-term consequences and stability of these changes remain to be seen.  Birds can manage perfectly well without additional feeding, but if you like to put out food for them they will be grateful, and you will see more of them in your garden.
 
Are there any negative issues over bird feeding?
 
There definitely are.  The biggest issue is that dirty bird feeders can and do transmit diseases between feeding birds. The worst affected species are the greenfinch Chloris chloris and chaffinch Fringilla coelebs which are susceptible to fatal avian trichomonosis caused by the protozoan parasite Trichomonas gallinae .  This is spread by infected birds wiping their beaks at feeders, and the disease picked up by subsequent visitors. Nationally, greenfinch numbers have dropped by 66% between the first outbreaks in 2006 and 20156..  As a result, the British race of greenfinch C. chloris harrisoni is now red-listed as endangered.
 
 
Old photo of great tits on a feeder set up by Steve Head.  I would now say this feeder is overfilled so it will take too long to be emptied and sterilised, risking disease spread.  Capacious feeders like this with multiple access holes are to be avoided.
Does bird feeding make a difference?
 
Research has shown that over 50 years the diversity of food types available, and consequently the diversity of species coming to feeders have grown markedly and has boosted the numbers of less common species seen in gardens. In urban Britain, species that exploit feeders are increasing in numbers, while populations of those that do not are unchanged2.. This study also showed that the effects of feeding outweigh those of winter temperature or local habitat. We have good evidence that bird-feeding in British gardens has had an evolutionary impact on blackcaps Sylvia atricapilla3..  Continental birds that once migrated to southern Spain in winter are now migrating to Britain, and these birds have become genetically different from those continuing to fly south.
Blackcap Sylvia atricapilla
Avian pox is a virus affecting several garden bird species, mostly rather mildly, but a much more dangerous variant appeared in 2006, mostly affecting the great tit Parus major. It seems to be mainly confined to the southern and eastern part of England and has caused population declines, although not as marked as for greenfinch6..
 
Another but lesser concern is Salmonella infection in small songbirds, but this has declined in incidence over the last ten years.  Finally, stale birdfood can be toxic through aflatoxin secreted by the moulds Penicillium and Aspergillus especially on peanut. Autopsies of dead house sparrows and greenfinches have detected the toxins, which have also been found at high levels in garden bird feeders6.. It remains unclear what if any effect this is having, but it would be very prudent to ensure only high-quality (human food grade) peanuts or seed are provided.
 
Conclusions
 
If you can’t clean your feeders regularly, it’s probably best not to use them.   Feeding birds is a good thing to do, but only if it has minimal risk of disease transmission. Put only enough food in the feeder to last a few days and clean it before refilling.  Remove any soggy or sprouting grain, then either put the feeder in a hot wash in the dishwasher, or clean it using dilute (1:9) bleach.  Dry it before refilling.
 
[Another protective tip is to hang feeders near (about 1m) from windows rather than further away.  This helps reduce the risk of dangerous high-speed window impacts7..]
 
References
 
1.  Cox DTC, Gaston KJ. (2018) Human–nature interactions and the consequences and drivers of provisioning wildlife. Phil. Trans. R. Soc. B 373: 20170092. http://dx.doi.org/10.1098/rstb.2017.0092
 
2.  Plummer, K.E., Risely, K., Toms, M.P. et al. The composition of British bird communities is associated with long-term garden bird feeding. Nat Commun 10, 2088 (2019). https://doi.org/10.1038/s41467-019-10111-5
 
3.  Plummer, K.E., Siriwardena, G.M. Conway G.J., Risely K. & Toms P. (2015) Is supplementary feeding in gardens a driver of evolutionary change in a migratory bird species? Glob. Chang. Biol. 21:4353-63.
 
4.  Conservation Evidence Adult survival  
 
5.  Conservation Evidence  Improve reproductive success 
 
6.  Lawson B, Robinson RA, Toms MP, Risely K, MacDonald S, Cunningham AA. (2018) Health hazards to wild birds and risk factors associated with anthropogenic food provisioning. Phil. Trans. R. Soc. B 373: 20170091. Available here 
 
7.  Conservation Evidence Feeder placement 
 
 
Page written by Steve Head: Reviewed by Ken Thompson
 
Greenfinch suffering from trichomonosis, sometimes called "fat finch disease"
Myth: It is always helpful to feed garden birds!
 
This is not so much a myth, as a bit of an exaggeration, and one that can have seriously bad effects if not done carefully.
 
Bird feeding is the most popular wildlife gardening activity in Britain, other than growing plants.  In a recent survey conducted by YouGov for the Wildlife Gardening Forum 41% of a randomly chosen set of householders said they acted to help wildlife a lot or a fair amount.  76% of them provided supplementary food for birds.  The wild bird food industry in Britain is huge, estimated at between £200m and £300m annually. It’s clear that feeding birds isn’t entirely altruistic, people enjoy watching them through the window without the need for heavy coats and binoculars. There is evidence that feeding birds has benefit for human wellbeing by bringing people closer to nature1..
 
 
 
 
 
 
Old photo of great tits on a feeder set up by Steve Head.  I would now say this feeder is overfilled so it will take too long to be emptied and sterilised, risking disease spread.  Capacious feeders like this with multiple access holes are to be avoided.
Does bird feeding make a difference?
 
Research has shown that over 50 years the diversity of food types available, and consequently the diversity of species coming to feeders have grown markedly and has boosted the numbers of less common species seen in gardens. In urban Britain, species that exploit feeders are increasing in numbers, while populations of those that do not are unchanged2.. This study also showed that the effects of feeding outweigh those of winter temperature or local habitat. We have good evidence that bird-feeding in British gardens has had an evolutionary impact on blackcaps Sylvia atricapilla3..  Continental birds that once migrated to southern Spain in winter are now migrating to Britain, and these birds have become genetically different from those continuing to fly south.
Blackcap Sylvia atricapilla
 
 
How feeding helps birds is reasonably clear. Published data show that in most cases supplementary feeding does increase adult bird condition and survival4., especially for females, in winter and during the breeding season. The effect on their reproductive success was much less clear, with as many studies suggesting it had no benefit as studies that found it improved fledging and survival. On balance it is considered likely to be beneficial5..
 
The popularity of bird feeding has created largely beneficial changes in our bird populations, although the long-term consequences and stability of these changes remain to be seen.  Birds can manage perfectly well without additional feeding, but if you like to put out food for them they will be grateful, and you will see more of them in your garden.
 
Are there any negative issues over bird feeding?
 
There definitely are.  The biggest issue is that dirty bird feeders can and do transmit diseases between feeding birds. The worst affected species are the greenfinch Chloris chloris and chaffinch Fringilla coelebs which are susceptible to fatal avian trichomonosis caused by the protozoan parasite Trichomonas gallinae .  This is spread by infected birds wiping their beaks at feeders, and the disease picked up by subsequent visitors. Nationally, greenfinch numbers have dropped by 66% between the first outbreaks in 2006 and 20156..  As a result, the British race of greenfinch C. chloris harrisoni is now red-listed as endangered.
 
 
Greenfinch suffering from trichomonosis, sometimes called "fat finch disease"
 
Avian pox is a virus affecting several garden bird species, mostly rather mildly, but a much more dangerous variant appeared in 2006, mostly affecting the great tit Parus major. It seems to be mainly confined to the southern and eastern part of England and has caused population declines, although not as marked as for greenfinch6..
 
Another but lesser concern is Salmonella infection in small songbirds, but this has declined in incidence over the last ten years.  Finally, stale birdfood can be toxic through aflatoxin secreted by the moulds Penicillium and Aspergillus especially on peanut. Autopsies of dead house sparrows and greenfinches have detected the toxins, which have also been found at high levels in garden bird feeders6.. It remains unclear what if any effect this is having, but it would be very prudent to ensure only high-quality (human food grade) peanuts or seed are provided.
 
Conclusions
 
If you can’t clean your feeders regularly, it’s probably best not to use them.   Feeding birds is a good thing to do, but only if it has minimal risk of disease transmission. Put only enough food in the feeder to last a few days and clean it before refilling.  Remove any soggy or sprouting grain, then either put the feeder in a hot wash in the dishwasher, or clean it using dilute (1:9) bleach.  Dry it before refilling.
 
[Another protective tip is to hang feeders near (about 1m) from windows rather than further away.  This helps reduce the risk of dangerous high-speed window impacts7..]
 
References
 
1.  Cox DTC, Gaston KJ. (2018) Human–nature interactions and the consequences and drivers of provisioning wildlife. Phil. Trans. R. Soc. B 373: 20170092. http://dx.doi.org/10.1098/rstb.2017.0092
 
2.  Plummer, K.E., Risely, K., Toms, M.P. et al. The composition of British bird communities is associated with long-term garden bird feeding. Nat Commun 10, 2088 (2019). https://doi.org/10.1038/s41467-019-10111-5
 
3.  Plummer, K.E., Siriwardena, G.M. Conway G.J., Risely K. & Toms P. (2015) Is supplementary feeding in gardens a driver of evolutionary change in a migratory bird species? Glob. Chang. Biol. 21:4353-63.
 
4.  Conservation Evidence Adult survival  
 
5.  Conservation Evidence  Improve reproductive success 
 
6.  Lawson B, Robinson RA, Toms MP, Risely K, MacDonald S, Cunningham AA. (2018) Health hazards to wild birds and risk factors associated with anthropogenic food provisioning. Phil. Trans. R. Soc. B 373: 20170091. Available here 
 
7.  Conservation Evidence Feeder placement 
 
 
Page written by Steve Head: Reviewed by Ken Thompson
 
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