Birds lay their eggs earlier and successfully rear more chicks to fledging stage in places where food is provided earlier in the year, researchers from Queen's University Belfast and the University of Exeter have discovered.

The study was carried out in 10 woodlands in Co Down and revealed that birds provided with feed laid their eggs an average of 2.5 days before the rest - even when feeding stopped more than six weeks before the first recorded laying date.

They also produced on average almost one extra chick per nest that made it to fledging, the research, published in Royal Society journal Biology Letters, found.

Trees in some of the woodlands were hung with wire mesh feeders which were kept supplied with peanuts from the start of November for early March. Other woodlands had no feed. The researchers also provided and monitored nest boxes, most of which were colonised by blue tits.

The extra winter food could be helping female birds enter the breeding season - which starts in April for most UK songbirds - in a better condition.

More chicks could be surviving because the parents are in a better physical condition and more able to look after the young, while foods such as peanuts and sunflower seeds also have micro-nutrients which could be passed onto offspring in the eggs, the scientists said.

UK and US households put out some 500,000 tonnes of food for garden birds each year, and the researchers said the study showed for the first time that the benefits of winter feeding could last into the breeding season.

The practice of putting out nuts and seeds could be having a major effect on numbers of birds such as finches and tits - although migratory birds returning to the UK in spring could be hit with knock-on effects if they face greater competition from species fed in the winter.

But the researchers warned there could be costs to laying early if it means the young are in the nest before maximum food is available - in which case the feeders are an "ecological trap", stimulating inappropriate breeding and affecting numbers.

Dr Stuart Bearhop, of the University of Exeter, said he was keen to investigate these side effects but promised he would be putting out food for garden birds in the meantime.