Guillemots (Murres) lay a very large single egg on a rock ledge devoid of nesting material. The egg is pear-shaped so that when it rolls it rotates around its apex & does not roll off the ledge.
Incubation lasts about 30 days. The youngsters usually leave the nesting ledges at 15-20 days of age -well before they have developed full feathering. The youngsters launch themselves off the cliff edge on immature stubby wings gliding steeply down to the sea below. Usually one adult is on the sea under the breeding ledge calling to encourage the youngster to leap whilst the other adult flaps down alongside the chick. The small family then paddles off into the sunset!!