This video from the USA says about itself:
Blue Jays Harass Screech Owl
1 May 2016
Mother red morph Eastern Screech Owl is trying to take a break outside the nest box in the daytime and let the fast growing owlets have some room and air to cool down. Ordinarily she would never expose herself in the daytime except for nesting season. The Blue Jays are not going to let her rest – they want to harass her until she leaves their nesting area, but she is not going to leave her nest box – thus a standoff.
Father Screech Owl sometimes kills songbirds roosting in the trees at night to feed the owlets so you can’t blame the Blue Jays. Screech Owls are very small owls and have different techniques to deal with threats including making themselves very skinny like a branch when a real dangerous threat is around like a hawk or big owl or puffing themselves up for some threats they can intimidate like squirrels. These behaviors can be seen in this documentary:
Eastern Screech Owl Camouflage and Defensive Survival Techniques