A new study, published on Wednesday, is the first large-scale experiment to prove that extra food put out in winter not only helps these birds to survive harsher weather but also enables them to have a more successful breeding season.

The test was conducted in isolated woodland in County Down, Northern Ireland. Nest boxes were nailed to trees.

One area of the wood was otherwise left untouched. It was a 'control' area to see how wild birds fared without food supplements.

In the other part of the wood, the scientists set up wire-mesh peanut feeders, replicating the type and volume of food typically put out in gardens in Britain in winter time.

Birds which lived at the 'supplement' site laid their eggs on average 2.5 days earlier than birds at the 'control' site.

The two sets of birds produced the same number of chicks but the fledglings of the 'supplement' group were far likelier to survive to the point where they could fly and leave the nest.

Nearly 80 per cent of this group fledged but the success rate in the 'control' group was just over 60 per cent.

'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,' suggested one of the authors, Stuart Bearhop of the University of Exeter in southwestern England.

'Foods like peanuts and bird seed also include vitamins and minerals which can also produce healthier eggs and chicks.' According to an estimate cited in the report, Britons and Americans put out more than 500,000 tonnes of food for the birds each year.

The paper appears in Biology Letters, published by the Royal Society, which is Britain's de-facto academy of sciences. -- AFP