Growing reports of outbreaks of infectious diseases in garden birds, including salmonellosis, provided further ammunition for these and other sceptics, who were then able to claim that by “putting out food” the public were encouraging birds to congregate in larger than usual numbers and thereby facilitate the spread of pathogens. In the absence of proper scientific evidence, people had to make up their own mind – and most, boosted by the greater availability of bird-feeding products of high quality, opted to continue. The authors of this Comment (John and Margaret Cooper) have always supported and encouraged the concept of feeding wild birds, mindful of how the pioneer of “bird gardening”, the naturalist Maxwell Knight (see remarks of Simon King and https://thefrightenedfaceofnature.com/) viewed the practice. Maxwell Knight and his wife Susi fed the birds in their garden for many years and came to the conclusion that if done sensibly and hygienically, this exercise appeared to cause no harm (individual birds were seen to return time and time again, sometimes in succeeding years), it probably did a lot to help birds in the winter and at other times of hardship, and (to the Knights perhaps the strongest argument) it brought ordinary people, including those unable to venture further afield, into closer contact with birds and the natural world. Now, thanks to the work of the BTO researchers, the need for ambivalence is over. We have convincing evidence of the value of garden bird feeding and the fact that it emanates from the BTO (British Trust for Ornithology), an internationally respected body that has been carrying out scientific studies on British birds since 1932, adds weight and credibility to the conclusions.
We have corresponded with two of the authors of the BTO report. Back in 2013 John first met and had interesting discussions with Dr Gavin Siriwardena, at a time when Haith’s was expressing concerns about the supplementary feeding of farmland birds – in particular, the possible adverse effects on avian health if the cereals being used were not of the highest quality. On this recent occasion, however, the topic of discussion was more positive – namely, how and why British bird populations are benefiting from long-term garden bird feeding. In our correspondence with Gavin we welcomed the findings of the recent BTO report but commented that there was no mention in it of the potential danger of spreading of pathogens (for instance, if the food being offered was not of the highest quality, or if presentation and hygiene were poor) nor of the potential danger to wild birds of inducing other (largely metabolic) diseases by overfeeding. Gavin responded
“You're right that we didn't directly discuss pathogen effects in the paper, but they are there in the patterns for greenfinch, at least. Kate's previous work has considered negative effects of "the wrong feeding" and this work is about changes in community structure that take multiple forms, including increases and decreases. This will probably include interspecific interactions and sub-lethal disease or diet effects could well be a part of these, although it would be very difficult to separate different types of interaction from survey data alone”
A follow-up letter from Dr Kate Plummer, the senior author of the report expanded on this as follows:
“As Gavin says, we were looking to describe the broad patterns that have occurred over time and across whole communities, so we didn't focus on the specific mechanisms by which food can influence bird numbers. But of course you are right, both positive and negative impacts of feeding have been described and all of these are encompassed by the overall community responses we present.
None of this is to suggest that the findings in the BTO study are anything but welcome. As Simon King points out, they substantiate Haith's long-held belief that it is correct to promote the importance and potential value of feeding garden birds and to couple this with the provision of food items of high quality.
To us, the important “take home message” resulting from the findings reported by the BTO researchers is:
What of the future? It is clearly most important that the findings in the BTO study are carried forward and that the mechanisms involved in the increase in numbers of some species are properly studied so that we understand them better. Population dynamics (“the study of the size and age composition of populations and the biological and environmental processes that influence them”) is, however, a remarkably complex discipline. An increase in bird numbers may be associated with, or due to, various interacting factors. The growth may in turn lead to other ecological changes, affecting diverse species (not just birds – insects, for example) and the wider environment. Future research will benefit from the input of members of the public, field naturalists and the bird food industry as well as ornithologists, ecologists, veterinarians and statisticians. All have a part to play if the encouraging trend in our garden birds reported by the BTO is to be sustained and the long-term health and welfare of our native avifauna is to be adequately protected and enhanced.
JEC/MEC 19th June 2019