Elizabeth Bigg said:
Ryan - I'm not sure how nuthatch chicks behave, but bluetits have no problem in getting out of the box, because they fly up to the hole. They practise their wing flapping for quite a while before they actually leave, sometimes flying up to look out of the hole. I should think nuthatches would do the same - after all they have to be able to fly as they leave home, so surely they must practise (within the limitations of the box) before their big day.
You are right Elizabeth, but if we maximise the birds' chances of escape, we maximise the yield on birds. By this I'm talking about the 'runt' of the clutch.
If the side of the box were rough, the runt could escape at the same time as the others, whereas in most cases it gets left behind and consequently dies.
By allowing the runt to leave the nest, we minimise the chances of a healthy youngster being taken by a predator. Cruel maybe, but true. In certain cases, the runt can mature in to an adult if only given a chance to survive the first few days.
This advice only comes from seeing hundreds and hundreds of Tit boxes, since my dad was a ringer for around twenty years and I used to help him.
Some folks will tell you that there is only one runt in a clutch, but there are usually two types (three if you like); unhatched eggs, young that die in the first day or two, and those who live to fledging age (1J) but are smaller (less developed) than the others.
The piece of cloth theory sounds eminently sensible and on a final note, don't put up a box if there are cats around, you may be doing more harm than good.