Empty bird feeders on your property for several days. If food is not readily available, the owls may go elsewhere.
Pen up chickens, rabbits or other small animals in secure pens at night. Owls are nocturnal -- they do most of their hunting after dark. Clear away brush and debris to discourage small animals from nesting and hiding.
Make your yard physically inhospitable to owl nesting. Install high tension wire or balloons in areas where owls have been seen, to prevent or discourage them from perching.
Frighten owls with flashing lights and loud noises. Shine a bright light on them in the tree. Set off firecrackers. Turn on lights and alarms for at least a week each time you spot the owl. Owls are territorial and will not go easily unless you continually disturb them.
Hire a pest management expert in your area to trap and relocate the owl.