The mother pigeon lies in the nest in the morning and does not lie in the nest at noon. At night, male pigeons sometimes bring grass into their nests.

According to the information you provided, I can assume that the female pigeon is hatching eggs and the male pigeon is also contributing to the hatching. The mother pigeon usually lies on the baby pigeon for warmth and protection in the morning and evening. The temperature is usually high at noon, so the mother pigeon may need to rest, so she is not in the nest.

The male pigeon sometimes brings grass into the nest, which may be that he is adding materials to the nest to better protect the young pigeons. The male pigeon will also provide food and protection for the mother pigeon and the soon-to-be-born young pigeon.

Generally speaking, this is normal behavior, indicating that your pigeon is actively incubating eggs to prepare for the arrival of new life. If you have any doubts about their health or behavior, you'd better consult a veterinarian or a professional.