When incubating eggs, the female will stay in the cavity for most of the night, leaving occasionally for reasons not totally clear to us. The male is often out all night hunting and will return with prey. The male may or may not spend the day in the cavity. If not, he will roost in a nearby tree, as many BNOWs do. As chicks hatch and grow, both adults will roost outside of the cavity during the day, and deliver food at night. Once chicks fledge, the cavity may go unused for sometime until this pair, or another pair, decide to use it again for roosting and breeding. However, chicks often use the cavity to roost during the day for several weeks after they fledge.
BNOWs lay one to up to a dozen or more eggs/year/per clutch (sometimes they have more than one clutch/year). A ‘clutch’ is a group of eggs laid in a nest at one time. Larger clutches sometimes result in not all chicks surviving. Two common reasons for this: 1) Not all the eggs always hatch. 2) When the female lays the first egg she begin incubating it, meaning development begins. It takes her 1.5 to 2 days to lay the next egg. So, for example, if she lays 7 eggs, it may have taken her two weeks to lay them all. They will hatch accordingly, each one after approximately 30 days. This means by the time egg #7 hatches, egg #1 (if it hatched) will already have 2 weeks of development under its belt. BNOW chicks can fly at around 8 weeks, so 2 weeks is a lot of development time and younger chicks are sometimes not strong enough to compete with larger, older siblings for food.
It’s approximately 30 days.