Update..

The heat from the past two days has slowed down the delivery of the food in the middle of the day..but activity in the morning and the evening is frenetic. The mother spent a lot of time rootling head down at the bottom of the nest and I see now that the nest is much larger.. the sides have risen and it is not so straight sided so there is more room for the chicks to shift about without escaping the nest. I exptect this is to contain them and not let any one escape the warmth of its siblings.
The father brought in a difficult bug today.. not sure what it was but it was put into the beaks of three of the chicks and removed again as they couldnt swallow it..eventually with much chirring the mother insisted he feed it to her.. she then tried again.. no success.. so she chopped it in two and fed two chicks!!!
I saw wing feathers today for the first time.. still bald on their backs.
Hatched 13th may
Noticed also that they are developing a marked stripe down their spine..