Instead of building
an actual nest, some birds choose a secluded location where they
can safely lay their eggs and raise their young. Some falcons and other
raptors choose isolated ledges or small caves in a cliff as
nesting sites. The shape of their eggs may play a part in some
instances. The Common Murre, Thick-billed Murre and
Razorbill, choose narrow ledges, where they lay very pointed eggs
which will roll in a circle instead of rolling of the ledge.
Elsewhere around the world other species of
birds choose out-of-the-way places instead of actual nests to
provide a safe environment to create offspring. Some
penguins of the southern hemisphere, will huddle in large groups
in very cold, remote places and hold their eggs on top of their
feet under a fold of belly skin to provide enough warmth to hatch
the eggs.
Peregrine
Falcons do not build their own nests but use remote ledges and
small caves in cliffs and bluffs and will also use nest of
other birds, usually of eagles, hawks and ravens.
Remote , by John Crawley
ŠJohn Crawley
They
lay from 2 to 6 eggs, but usually 3 or 4 and incubate them for 28
or 29 day. Young birds will fly after 35 to 42 days after
hatching.
Young fast-growing Peregrine, by John Crawley
ŠJohn Crawley
Peregrine
Falcons do not build their own nests but use remote ledges and
small caves in cliffs and bluffs and will also use nest of
other birds, usually of eagles, hawks and ravens. 
They
lay from 2 to 6 eggs, but usually 3 or 4 and incubate them for 28
or 29 day. Young birds will fly after 35 to 42 days after
hatching.