Wood Pigeon nest

When trimming back the wisteria, we discovered a wood pigeon nesting just outside our window. My daughter is in love with watching them and we are happy for them to remain there. 

I am curious to know why there is only one adult pigeon - unsure if male or female. Researching, it is uncommon for there to be just one adult.

Also, since discovering the nest, she/he has not left and we have not seen her feed her babies. It has been two days now. Is this unusual?The babies appear to be just in the first week of their lives.