The African grey hornbill (Tockus nasutus) is a member of hornbill family found in the Old World*, and is a widespread and common resident breeder in much of Sub-Saharan Africa and into Arabia.
But before a new individual of the kind enters the world, it faces a harsh double obstacle wherein it must first break out of its shell, and then demolish the walled-up entrance to its specially built ‘nursery’.
The female lays two to four eggs in a tree trunk cavity, which it covers from the inside during incubation using a cement made of mud, droppings, fruit pulp and saliva. There is one narrow aperture just big enough for the male to transfer food to her and the chicks.
Incubation of the eggs lasts for about five weeks, and when they hatch she breaks through the wall, but leaves her brood behind. The mother bird repairs the damage at once by reconstructing the wall-often helped by the chicks on the inside. After this, the chicks are fed by both the parents through the small hole in the wall.
It is only when the chicks are strong enough do they attack the wall with their beaks, and emerge into the welcoming outside world.
*The Old World is used in the west to refer to Africa, Europe, and Asia (Afro-Eurasia), regarded collectively as the part of the world known to Europeans before contact with the Americas. It is used in the context of, and contrasts with, the New World (Americas).