How much food does a garden bird eat?

The long-running series in which readers answer other readers’ questions on subjects ranging from trivial flights of fancy to profound scientific conceptsLike many people I have birdfeeders in my garden. I fill mine with sunflower hearts and regularly put in about 1.5kg a day. This gives rise to the question, how much food does a garden bird consume? The species visiting are, as one might expect, finches, tits and robins, with the occasional nuthatch and great spotted woodpecker.Graham Wil