Question
HELP!
We have owls roasting in our trees, their droppings and food regurgitation are making a huge mess of our vechile and sidewalk.  What can we do to get rid of them?  

Answer
Wow. I would love some photos of that. [email protected]
I notice you use the plural for owls. That would be very unusual.
The simple solution would be to trim the branches over hanging the area where you don't want the owls to roost.

You can also illuminate the spot with lights to help annoy the birds.

If those techniques don't work, write back for the next step.