Nesting time

A great tit has built a nest in one of my boxes, and today for the first time she let us see that she has laid four eggs.  She's started sitting now, but might lay another one tomorrow.  Her mate appeared a few times today, with food.  What has also been interesting is that a blue tit has been going into the box and sniffing around, and it became clear today that it was stealing nesting material.  With mother great tit settled to incubate now, I don't think the blue tit will be able to do that again.