| Summary: | Post-fledging parental care is generally little studied in birds. By use of radio telemetry, I studied the post-fledging parental behaviour of female great grey owls (Strix nebulosa), measured as number of prey deliveries from males and females and female aggressiveness and brood defence. I also observed the behaviour and movement patterns of the dependent fledged juveniles. The females provided care by staying near the young to guard them and assisting the males with food provisioning. No female deserted the male and offspring before the study was terminated. The males provided more than twice as many prey items for the offspring than the females did in the post-fledging dependence period, and the probability of a female delivering a prey tended to increase with brood size. Females also delivered more prey items when the ambient temperature was low. When a male had captured a prey, he delivered it directly to the fledglings in 83% of the cases, and if he delivered it to the female instead, it was usually under stressful situations. The female spent much time near the fledglings, but the probability of her being absent increased with increased fledgling age and brood size. When intruders were approaching the fledglings, the female could show an extremely aggressive behaviour, and female aggressiveness depended on observer behaviour and decreased with increasing fledgling age. An alternative defence strategy of the female was to perform distraction displays, and the probability of her doing so decreased with brood size. The fledglings moved away from the nest as they aged, and the distance from the nest significantly increased with increasing fledgling age. However, the siblings stayed close to each other during the entire post-fledging dependence period. The juvenile mortality rate from fledging until the fledglings could fly and escape predators was 38%, and the highest mortality rate occurred the first time after fledging. Increasing perching height, staying near siblings and moving towards the parent’s ...
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