Aegolius_funereus is primarily monogamous. However, there have been documented cases of both bigyny (one male with two mates) and biandry (one female producing two clutches by two different mates). These cases have been observed only in Eurasia, and only when food is extremely plentiful. Males don't defend large foraging territories, but rather nest sites (old woodpecker holes), which are often in short supply. Fights between males have not been observed, and it appears that they compete for females through song and flight. Males will fly between perches near females, and sing a courtship song to attract female interest. If a female is interested, she will inspect the nest and, if she accepts it, she will simply stay there. The courtship period might last anywhere from 2 to 6 weeks for individual owls and from 1 to 4 months for the population as a whole.
Mating System: monogamous
Breeding season is variable, but takes place most commonly from March to June. Clutch size varies with food availability, but is typically around 4 or 5. Eggs are laid once every two days and brooding begins with the first egg, so hatching is asynchronous. Incubation is typically 28 days long. Young fledge about 30 to 31 days after hatching. The young are cared for by their parents for about a 6 weeks after fledging before setting out on their own. They become sexually mature in their first year, at around nine months old.
Breeding interval: Boreal owls typically breed once yearly. If food is plentiful then multiple clutches may occur.
Breeding season: Breeding season is highly variable, but is typically from the end of February to as late as July.
Range eggs per season: 2 to 7.
Average eggs per season: 5.
Range time to hatching: 25 to 32 days.
Range fledging age: 28 to 36 days.
Range time to independence: 6 to 7 weeks.
Range age at sexual or reproductive maturity (female): 9 to 9 months.
Range age at sexual or reproductive maturity (male): 9 to 9 months.
Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization
Average eggs per season: 5.
Boreal owls provide considerable care for their young, both before and after hatching. Females stay near the nest about a week before egg laying. During this pre-fertilization time, males hunt for themselves and bring food back to their mate. After the clutch has been laid, males continue to provide food for females, but otherwise stay away from the nest. Females incubate the eggs, leaving once daily to eliminate waste. After hatching, males bring food for females and nestlings. Females tear food into smaller pieces that the nestlings can swallow, until they become big enough to eat prey whole. Brooding occurs as long as there is still young in the nest. The final young typically fledges after about 4 weeks from the start of incubation. Once the young have fledged, they stay close to the nest site for about a week, and both parents bring food to them at night, homing in on the begging calls of the fledglings. At the end of the week, the fledglings begin to move farther away, but are still fed for some time by the parents. They finally become independent about six to seven weeks after hatching.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Male, Female); pre-hatching/birth (Provisioning, Protecting: Female); pre-weaning/fledging (Provisioning: Male, Protecting: Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female)