We have seen concern in our brood and other broods of owlets about the smallest owlet and why its so much smaller then the others, and if it’s OK and maybe something is wrong with it.
Most bird species don't start to incubate (warm) their eggs until the clutch is complete so the eggs hatch at more or less the same time.
Barn Owls begin incubation as soon as the first egg is laid and additional eggs are added every two to three days. This is termed "asynchronous" hatching.
( do I see a trivia question here ) The average hatching success rate is 4.5 and the age difference between the oldest and youngest nestlings can be as much as three weeks.
Compared to other owl species, Barn Owls lay small eggs (in relation to their body size) and they lay lots of them.