Keep feeding the birds over winter: that's the message from research by the University of Exeter and Queen's University Belfast, published today (6 February 2008) in the Royal Society journal Biology Letters. The study shows for the first time that the extra food we provide garden birds in winter makes for a more successful breeding season in the spring.
By providing some birds with extra food, such as peanuts, and leaving others to fend for themselves, the team was able to compare productivity between the two groups. Those that were given extra food laid eggs earlier and, although they produced the same number of chicks, an average of one more per clutch successfully fledged. Although it was well known that garden feeding helps many birds survive the winter, this is the first time that the benefits to spring breeding and productivity have been shown.
Dr Stuart Bearhop of the University of Exeter, corresponding author on the paper, said: "Our study shows that birds that receive extra food over winter lay their eggs earlier and produce more fledglings. While this research shows how the extra food we provide in winter helps the birds that take it, it is still unclear whether this has a knock-on effect on other species. This is something we are keen to investigate, but in the meantime I will certainly be putting out food for garden birds for the rest of the winter."
US and UK households provide over 500,000 tonnes of food for garden birds each year. Despite this, there is a debate on whether we should continue feeding birds in the spring, when natural food sources become more readily available. This research shows, for the first time, that birds will continue to benefit from winter feeding well into the breeding season, which starts in April for most song birds in the UK.
Dr Dan Chamberlain of the British Trust for Ornithology, a collaborator on the project, adds "These results demonstrate that feeding birds in gardens over winter can be vital to their breeding success. It is highly likely that the benefits of extra food continue year-round, so don't just stock your bird feeders in winter if you want to do the best for the birds in your garden".
Now that the research team has shown the long-lasting benefits of supplementary food for garden birds, they are keen to investigate exactly what is happening in terms of nutrition. Dr Stuart Bearhop of the University of Exeter continued: "The extra food we put out for birds contains fat, protein and carbohydrates, which may make the female bird stronger and more able to produce eggs. Foods like peanuts and bird seed also include vitamins and minerals, which can also produce healthier eggs and chicks, and we currently have a research project looking at the role of energy versus vitamins in explaining these effects."
The study was carried out by the University of Exeter, Queen's University Belfast, Central Science Laboratory, the British Trust for Ornithology and the University of Birmingham. Food and nestboxes were provided by Gardman Ltd.