What's actually more important is how long you let food remain in feeders, on a table or on the ground. This often isn't an issue because it won't be there long enough to create a problem! At certain times of year though (often late summer when natural food is more plentiful) uneaten food can build up and this can cause problems - in particular if the food gets damp or wet on a table or on the ground (food will normally stay dry in feeders, but may get damp in very wet and windy conditions). So as a basic guide:
- If food on a table or the ground gets damp or wet, then remove it after two days or so.
- Food in a tube or softfood feeder should be fine for up to 10 days (though in reality it's unlikely it would last that long) so remove it after this time and put fresh in.
- If extreme wet and windy weather makes food damp in a tube feeder, then remove it and put fresh in.
- Peanuts in mesh feeders can go mouldy in damp conditions. So keep an eye on them and replace as soon as there are any signs of mould. If it's both mild and damp, then generally one week is as long as peanuts will stay in good condition.
- Suet blocks and fat balls will also go mouldy in damp conditions so keep an eye on these and replace as soon as there are any signs of them degrading.
If you've been feeding birds for a while, then most of the above won't be a problem because you'll know how much food to put out at different times of the year. And if there is a problem, then it's normally the complete opposite - empty feeders as you try and keep up with demand!